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        INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY

        WORLD HEALTH ORGANIZATION



        TOXICOLOGICAL EVALUATION OF CERTAIN
        VETERINARY DRUG RESIDUES IN FOOD



        WHO FOOD ADDITIVES SERIES 41





        Prepared by:
          The 50th meeting of the Joint FAO/WHO Expert
          Committee on Food Additives (JECFA)



        World Health Organization, Geneva 1998




    IMIDOCARB

    First draft prepared by
    Dr E.A.M. Good
    Veterinary Medicines Directorate
    Addlestone, Surrey, United Kingdom

    1    Explanation
    2.   Biological data
         2.1  Biochemical aspects
              2.1.1  Absorption, distribution, and excretion
              2.1.2  Biotransformation
         2.2  Toxicological studies
              2.2.1  Acute toxicity
              2.2.2  Short term toxicity
              2.2.3  Long-term toxicity and carcinogenicity
              2.2.4  Genotoxicity
              2.2.5  Reproductive toxicity
              2.2.6  Special studies to investigate serum prolactin
                     concentrations
              2.2.7  Special studies on microbiological activity
              2.2.8  Special studies on pharmacodynamic effects
         2.3  Observations in humans
    3.   Comments
    4.   Evaluation
    5.   References

    1.  EXPLANATION

         Imidocarb is a carbanilide derivative that has been used for more
    than 20 years for the treatment of certain protozoal diseases,
    including babesiosis and anaplasmosis, in cattle, horses, sheep, and
    dogs. Imidocarb has not previously been reviewed by the Committee.

         The chemical name of imidocarb is
     N,N'-bis[3-(4,5-dihydro-1 H-imidazol-2-yl)phenylurea. The structure
    of imidocarb is shown in Figure 1.

         Most of the biological and toxicological studies that are
    reviewed below were carried out using imidocarb dipropionate with a
    purity close to 100%.

    FIGURE 1

    2.  BIOLOGICAL DATA

    2.1  Biochemical aspects

    2.1.1  Absorption, distribution, and excretion

         Studies in mice, rats, dogs, monkeys, and cattle have been
    reported. Most of them were carried out during the 1960s and 1970s
    according to the standards of those days, and important details are
    missing from some of the reports. In contrast, the study in cattle was
    certified for compliance with GLP.

          Mice

         Mice were injected into the tail vein with of 1 mg/kg bw
    imidocarb dihydrochloride radiolabelled with 14C in the carbonyl
    group. No radiolabel was detected in expired air. Excretion in the
    urine was initially very rapid but quickly slowed and continued
    throughout the observation period of 96 h. Faecal excretion followed a
    similar pattern. Of the recovered radiolabel (90% of the administered
    dose), about two-thirds was found in the urine and one-third in the
    faeces (Wander, 1968a).

          Rats

         Wistar rats were dosed orally with 14C-imidocarb dipropionate
    or 14C-imidocarb dihydrochloride and killed at various intervals up
    to 48 h after treatment. Another rat was dosed subcutaneously with the
    hydrochloride. Whole-body autoradiography indicated poor oral
    absorption of both salts, and radiolabel was detectable only in the
    liver, kidney, and gut. After subcutaneous treatment, a significant
    amount of radiolabel remained at the injection site (Farebrother,
    1973). In another study with various dose regimes and routes of
    administration (oral, intraperitoneal, subcutaneous), the highest
    concentrations of residues were found in the liver and kidney.
    Residues were still detectable in these organs 55 days after
    subcutaneous treatment with 5 mg/kg bw of the test substance.
    Excretion was slow in rats treated subcutaneously, and only 20% of the
    administered dose was recovered in excreta during the 78 h of
    treatment (Nimmo-Smith, 1968). In a preliminary study to investigate
    tissue retention, Wistar rats were given either a single oral dose or
    30 daily oral doses of 5 mg/kg bw imidocarb dipropionate. The rats
    were killed 24 h after the last dose, and residues in selected tissues
    were determined by an unspecified analytical method. The highest
    concentrations were found in kidney; surprisingly, the concentrations
    in liver and brain were higher after the single-dose regime (Thomson,
    1975a).

          Dogs

         Male beagle dogs were given daily oral doses of 5 mg/kg bw
    imidocarb dipropionate for 30 days and killed 24 h after the last
    dose. The residues were determined in selected tissues by an
    unspecified method. The highest concentrations were found in liver and
    then in kidney; no residues were detected in muscle or brain (< 500
    g/kg) (Chesher et al., 1976). In another study, mongrel dogs were
    given an intravenous bolus of 4 mg/kg bw of imidocarb dipropionate.
    The pharmacokinetics were biphasic and indicated a large volume of
    distribution. The mean terminal half-life was 207 min (Salam & Baggot,
    1983).

          Monkeys

         Female patas monkeys were given daily oral doses of 5 mg/kg bw
    imidocarb dipropionate for 30 days and were killed some time after the
    last dose (probably 24 h, although this is not stated). The residues
    were determined in selected tissues by an unspecified method. The
    highest concentrations were found in kidney and liver; none were
    detected in muscle or brain (limit of detection, 500 g/kg) (Thomson,
    1975b).

          Cattle

         In a study which complied with the principles of GLP, six
    lactating cows and eight calves were given a single subcutaneous
    injection of 3 mg/kg bw 14C-imidocarb dipropionate with a specific
    activity of 22 mCi/g. The test substance was formulated as the
    proprietary product Imizol Injection. A mean peak blood concentration
    of 1300 g-equivalents/kg was attained 1 h after treatment, and the
    concentration remained at this level for about 4 h, when 7291% of the
    radiolabel was bound to plasma proteins. Excretion was very slow: over
    the first 10 days, only 53% of the dose was recovered in excreta, with
    38% in the faeces and 15% in the urine. The residues in tissues were
    very persistent, particularly in liver where mean residues of 2200
    g-equivalents/kg were found 90 days after treatment (Ferguson, 1996).

    2.1.2  Biotransformation

         In bovine liver preparations  in vitro, there was no evidence
    for metabolism of imidocarb (Coldham et al., 1995).

          Mice

         Mice injected with 14C-imidocarb into the tail vein excreted
    37% of the administered dose in the urine within 2 h. Of the
    radiolabel in the urine, 95% was unmetabolized imidocarb. The mice
    were killed 3.5 h after treatment, and 29% of the dose was found in
    the liver, 6.8% in the kidney, and less than 1% in the gall-bladder.
    More than 90% of the radiolabel in these organs was unmetabolized
    imidocarb (Wander, 1968b).

          Cattle

         In the study described above in which cattle were treated
    subcutaneously, the main component of the residues in liver, kidney,
    muscle, and fat for up to 90 days after treatment was unmetabolized
    imidocarb. Minor components, accounting for not more than 10% of the
    total residues, were also present but were not identified. Imidicarb
    was also the major component of cows' milk, urine, and faeces
    (Ferguson, 1996).

    2.2  Toxicological studies

    2.2.1  Acute toxicity

         The results of studies of the acute toxicity of imidocarb are
    summarized in Table 1. None of the studies complied with GLP, and the
    reports fall short of modern standards. The signs of toxicity were
    generally consistent with the anticholinesterase activity of imidocarb
    and included lethargy, salivation, lachrymation, muscle fasciculation,
    ataxia, tremors, and convulsions. Congestion of the lung and kidneys
    and mottling of the liver were frequent post-mortem findings in the
    rats that died.

         In a published report, the signs of toxicity in groups of goats
    given a single intramuscular dose in the range 12-24 mg/kg bw included
    salivation, frequent urination and defaecation, weakness of the legs,
    abnormal posture, and recumbency. There were dose-related decreases in
    haemoglobin and erythrocyte counts and packed cell volume and
    dose-related increases in asparate aminotransferase activity and in
    creatinine and bilirubin concentrations. Serum cholinesterase activity
    was reduced in a dose-related manner. No significant effects were
    observed at 6 mg/kg bw. The effects were ameliorated by pretreatment
    with atropine sulfate intramuscularly at a dose of 1 mg per animal
    (Ali et al., 1985).

         Whole-blood cholinesterase activity was significantly reduced in
    calves given an intramuscular injection of 3.3 mg/kg bw imidocarb
    dipropionate. Maximum depression occurred about 30 min after
    treatment, and significant recovery was observed within 6 h. The
    cholinesterase depression did not correlate with the intensity of the
    clinical response (Michell et al., 1986).

    2.2.2  Short-term toxicity

          Mice

         A study in mice, intended as a range-finding probe for a study of
    dominant lethal mutations, was not carried out in accordance with GLP.
    Groups of six male Evans No. 1 mice were given daily intramuscular
    doses of 0 (distilled water), 7.8, 16, 31, 63, or 130 mg/kg bw per day
    of imidocarb dipropionate (expressed as base) for five days. Signs of
    toxicity were recorded for up to 14 days after the last dose. No blood
    chemistry or pathological examinations were carried out. All of the


        Table 1. Results of studies of acute toxicity with imidocarb

                                                                                                                                             
    Species                Route          Vehicle                    Sex     LD50          Salt                  Reference
    (strain)                                                                 (mg/kg bw)    administered
                                                                                                                                             

    Mouse (ICR)            Oral gavage    Sterile distilled water    M       723a          Dipropionate          Szot (1973)
    Mouse (ICR)            Oral gavage    Sterile distilled water    F       646a          Dipropionate          Szot (1973)
    Mouse (SAS)            Oral gavage    0.9% saline                F       544a          Dihydrochloride       Follenfant & Green (1971a)
    Mouse (SAS)            Oral gavage    0.9% saline                F       863a          Diacetate             Follenfant & Green (1971a)
    Mouse (SAS)            Oral gavage    0.9% saline                F       702a          Dipropionate          Follenfant & Green (1971a)
    Mouse (Gambles)        Oral gavage    0.9% saline                M       1400          Dihydrochloride       Green & Hughes (1969)
    Rat (Wistar)           Oral gavage    0.9% saline                F       1500          Dihydrochloride       Green & Hughes (1969)
    Rat (Wistar)           Oral gavage    0.9% saline                M       1652a         Dihydrochloride       Follenfant & Green (1971a)
    Rat (Wistar)           Oral gavage    0.9% saline                M       1216a         Diacetate             Follenfant & Green (1971a)
    Rat (Wistar)           Oral gavage    0.9% saline                M       1251a         Dipropionate          Follenfant & Green (1971a)
    Rat (Long Evans)       Oral gavage    Sterile distilled water    M       454a          Dipropionate          Szot (1973)
    Rat (Long Evans)       Oral gavage    Sterile distilled water    F       650a          Dipropionate          Szot (1973)
    Rabbit (New Zealand    Oral gavage    Water                      M + F   317           Dipropionate (27%     Piercy & James (1975)
    white)                                                                                 aqueous solution)     
    Rat (Long Evans)       Intravenous    0.9% saline                M       32.7a         Dipropionate          Szot (1973)
    Mouse (ICR)            Intravenous    0.9% saline                M       22.3a         Dipropionate          Szot (1973)
    Mouse (Gambles)        Intravenous    0.9% saline                M       16            Hydrochloride         Green & Hughes (1969)
    Mouse (SAS)            Subcutaneous   0.9% saline                F       78.6a         Dihydrochloride       Follenfant & Green (1971b)
    Mouse (SAS)            Subcutaneous   0.9% saline                F       94.5a         Diacetate             Follenfant & Green (1971b)
    Mouse (SAS)            Subcutaneous   0.9% saline                F       92.1a         Dipropionate          Follenfant & Green (1971b)
    Mouse (Gambles)        Subcutaneous   0.9% saline                M       140           Hydrochloride         Green & Hughes (1969)
    Rat (Wistar)           Subcutaneous   0.9% saline                F       150           Hydrochloride         Green & Hughes (1969)
    Rat (Sprague-Dawley)   Oral gavage    Water                      F       > 631a        Dipropionate (10%     Harper et al. (1997a)
                                                                                           aqueous solution)
    Rat (Sprague-Dawley)   Oral gavage    Water                      M       > 1000a       Dipropionate (10%     Harper et al. (1997b)
                                                                                           aqueous solution)
    Rat (Sprague-Dawley)   Oral gavage    Water                      F       1011.5a       Dipropionate (10%     Harper et al. (1997c)
                                                                                           aqueous solution)
    Rat (Sprague-Dawley)   Oral gavage    Water                      M       1998a         Dipropionate (10%     Harper et al. (1997d)
                                                                                           aqueous solution)
                                                                                                                                             

    a The LD50 values found in these studies are for the base.  In the remaining studies, the results are believed to be quoted as the salt,
      although this is not clear from the report in all cases.
    

    animals at 63 and 130 mg/kg bw and 50% of those at 31 mg/kg bw died
    three to four days after the start of treatment. The signs of toxicity
    were slow respiration and lethargy. There was no NOEL (Harper & James,
    1977).

          Rats

         In a preliminary study designed primarily to investigate
    distribution in tissues, groups of five female Wistar rats were given
    either a single oral dose of 5 mg/kg bw imidocarb dipropionate
    dissolved in distilled water, or daily oral doses of 5 mg/kg bw per
    day for 30 days. Five additional rats formed a control group. Blood
    samples were taken for haematological and clinical chemical testing,
    and electrocardiographic, ophthalmoscopic, and urinary measurements
    were made before treatment and at termination; no histopathological
    examination was performed. The rats were killed 24 h after the last
    dose, and residues were determined in selected tissues. There were no
    treatment-related effects on most of the parameters investigated. The
    significant changes in blood parameters included increased total
    leukocyte counts in the treated group; however, the toxicological
    significance of these effects is doubtful since satisfactory blood
    samples were obtained from only three treated rats (Thomson, 1975a).

         In a study that did not conform to GLP, groups of 10 Wistar rats
    of each sex were given daily oral doses of imidocarb dihydrochloride
    for three months. The study was carried out in two phases. In phase 1,
    the doses were 0 (distilled water), 125, 250, or 500 mg/kg bw per day;
    in phase 2, the doses were 0, 500, 750, or 1500 mg/kg bw per day. It
    was not clear whether the doses were expressed as the hydrochloride or
    as the the base, and the solutions were not analysed. The rats were
    weighed and examined daily. Blood samples for haematological and
    clinical chemical determinations were taken just before termination.
    Urinalysis was not carried out.

         All rats given 1500 mg/kg bw died. The body-weight gain of all
    treated rats was significantly lower than that of controls in phase 2.
    There were no significant changes in haematological or clinical
    chemical values, but changes were seen in the weights of a number of
    organs in animals at 500 or 750 mg/kg bw, including a significant
    reduction in absolute (but not relative) prostate weight, increased
    relative adrenal and thyroid weights in males, and increased relative
    adrenal weight in females. Pathological changes described as cloudy
    swelling were reported in the livers of 5/9 male and 7/10 female rats
    given 125 mg/kg bw and in all males and 6/10 females given 250 mg/kg
    bw, but in none of the controls. The lesion was reported to be
    reversible, but no evidence was provided. No histopathological
    examinations were carried out on rats at 500 or 750 mg/kg bw. No NOEL
    was identified (Bushby, 1970).

         Groups of Charles River rats were fed diets containing 0, 630,
    1900, or 9400 mg/kg imidocarb dipropionate for up to 90 days,
    according to the schedule shown in Table 2. The purpose was to
    identify the appropriate doses for a long-term study of toxicity. The
    study did not comply with the principles of GLP. The animals were
    checked daily for deaths, and body weight and food consumption were
    recorded weekly. Haematological and clinical chemical determinations
    were carried out on five rats of each sex per dose before treatment
    and during weeks 4 and 13. Five rats of each sex from the control
    group and those at the highest dose were killed after seven weeks and
    the remaining rats after 13 weeks. At both 7 and 13 weeks,
    acetylcholinesterase activity was measured in one-half of the brain of
    each of five rats of each sex in the control group and that at the
    highest dose At termination, each rat was examined grossly.
    Histopathological examinations were performed on 17 organs or tissues
    from five rats of each sex in the control group and that at the
    highest dose and on the livers, kidneys, and grossly abnormal tissues
    from the other rats.

        Table 2.  Achieved dosages in a 90-day study with imidocarb in Charles River rats

                                                                                   

    Concentration in    Males                         Females
    feed (mg/kg)                                                                   
                        No. rats    Achieved dose     No. rats    Achieved dose
                                    (mg/kg bw                     (mg/kg bw
                                    imidocarb base)               imidocarb base)
                                                                                   

    0                   15          0                 15          0
    630                 10          26                10          32
    1900                10          75                10          100
    9400                15          420               15          550
                                                                                   
    
         One male given 9400 mg/kg feed died during week 2, and a control
    female died during week 6. No signs of overt toxicity were observed.
    Body-weight gain was significantly reduced towards the end of the
    study in animals of each sex given 9400 mg/kg feed. There were no
    significant effects on haematological, clinical chemical, or urinary
    parameters or on brain acetylcholinesterase activity. Pathological
    changes attributable to treatment were limited to the livers of rats
    given 9400 mg/kg feed; the changes consisted of mild stasis of the
    bile in the canaliculi in one male and four females. The NOEL was 1900
    mg/kg feed, equal to 75 mg/kg bw per day (Hart, 1973a).

         Another study was conducted, which did not comply with the
    principles of GLP and was intended to be a two-year study of toxicity,
    but in which 117 rats died as a result of overheating of the animal
    rooms during week 37. The study was terminated during week 44, when
    all surviving rats were necropsied. In this study, groups of
    50 Sprague-Dawley rats of each sex were to have received diets
    containing the equivalent of 0, 75, 225, or 750 mg/kg bw per day of
    imidocarb dipropionate. The rats were F1a weanlings from groups at
    the corresponding doses in a study of reproductive toxicity; however,
    the highest dose was fetotoxic, so that there were insufficient
    weanlings available to form this group, and additional rats were
    purchased. No data were reported on this group.

         Until the overheating episode, there were no significant effects
    on body weight, food consumption, or haematological, clinical
    chemical, or urinary parameters. During the last five weeks, the food
    intake of females at 225 mg/kg bw was increased, but they showed no
    change in body weight. At week 44, the mean thyroid:body weight ratio
    was increased in females at this dose. There were no significant
    pathological findings. No firm conclusions could be drawn from this
    study (Hart, 1974a).

          Dogs

         In a study that did not comply with GLP, a group of five male
    beagle dogs, described as 'substandard', was given daily oral doses of
    5 mg/kg bw imidocarb dipropionate (expressed as base) in distilled
    water for 30 days. There was no untreated control group. No signs of
    toxicity were observed and there appeared to be no adverse effects on
    body weight, food or water intake, or haematological or clinical
    chemical parameters. The dogs were killed 24 h after the last dose,
    and urine was taken for determination of pH, protein, glucose, ketone,
    and blood. Selected organs were weighed and a gross pathological
    examination was carried out on each dog. There were no obvious
    substance-related changes (Chesher et al., 1976).

          In another study that did not comply with GLP, groups of four
    beagle dogs of each sex were given daily oral doses of 0, 5, 20, or 80
    mg/kg bw per day imidocarb dipropionate (expressed as base) in gelatin
    capsules, for 90 days. The animals were weighed twice weekly, and each
    dog was subjected to an ophthalmoscopic examination before treatment
    and on days 36 and 76. Blood samples were taken from all dogs for
    haematological and some clinical chemical investigations before
    treatment and on days 7, 28, 56, 71, and 90; cholinesterase activity
    was not monitored. Urine samples were collected at necropsy. About 25
    tissues from each animal were examined microscopically.

         All four males and two of the females given 80 mg/kg bw per day
    died or were killed  in extremis after having reduced food intake and
    weight loss for about two weeks before death. The signs of toxicity in
    this group included weakness, recumbency, salivation, muscle
    fasiculation, ataxia, and splayed hind legs, probably indicating an
    anticholinesterase effect. The food intake of dogs at 20 mg/kg bw was

    transiently reduced. There were no treatment-related ophthalmoscopic
    changes. Eosinophilia was observed in some dogs given 20 or 80 mg/kg
    bw per day, and those at the highest dose showed a trend towards
    increased serum alanine and aspartate aminotransferase activity and
    bilirubin concentration, with occasional, transient increases in those
    at 20 mg/kg bw per day. The absolute and relative weights of the
    pituitary were decreased in dogs at 20 but not at 80 mg/kg bw per day,
    but animals at 80 mg/kg bw per day showed significant increases in the
    absolute and relative weights of the kidney, adrenal, and thyroid.
    Gross examination revealed fatty changes and mottling in the livers,
    particularly in dogs given 20 or 80 mg/kg bw per day.

         Histological changes were observed in a range of tissues from
    dogs at 80 mg/kg bw per day, particularly in the thymus, spleen, lymph
    nodes, and stroma of the villi of the small intestine (pyknosis and
    karyorrhexis), and fatty changes were observed in the thick section of
    the loop of Henle and the distal convoluted tubules. The liver showed
    haemorrhagic necrosis, fatty changes, granularity, or vacuolation of
    the hepatocytes. Similar though less severe changes were observed in
    the livers of dogs given 20 mg/kg bw per day. The NOEL was 5 mg/kg bw
    per day (Reynolds et al., 1977).

          Monkeys

         In a preliminary study designed to investigate distribution to
    tissues, five female patas monkeys were given daily oral doses of
    5 mg/kg bw per day imidocarb dipropionate dissolved in distilled water
    for 30 days. A control group of five females was left untreated. Blood
    samples were taken before treatment, seven and 14 days after the start
    of treatment, and at termination. Some time after the last dose (not
    stated), the treated monkeys were killed and examined for gross
    changes; the control monkeys were not autopsied. There were no signs
    of toxicity in the treated animals, and no effects were observed on
    haematological or clinical chemical values or gross appearance
    (Thomson, 1975b).

    2.2.3  Long-term toxicity and carcinogenicity

          Rats

         In a study that did not conform to GLP, groups of 50 Wistar rats
    of each sex were fed diets calculated to provide intakes of 0, 15, 60,
    or 240 mg/kg bw per day imidocarb dipropionate (expressed as base) for
    104 weeks. Satellite groups of 15 rats of each sex per dose were used
    for collection of blood and urine before treatment and at regular
    intervals up to termination. Ophthalmoscopic examinations were carried
    out at intervals throughout the study on controls and animals at the
    highest dose. At termination, about 25 tissues were selected for
    histopathological examination from 10 controls of each sex and from
    four males and 19 females at the highest dose; eight or nine tissues
    were examined from the remaining animals, comprising lymph nodes,

    liver, spleen, kidneys, ovaries, adrenals, thyroids, pituitaries, and
    blood films. Gross lesions from all animals were also examined
    microscopically.

         Survival of animals at the highest dose was adversely affected,
    only 9/65 males surviving to termination. The rats in this group
    became emaciated, their body-weight gain being significantly reduced
    and food consumption significantly increased; females were less
    severely affected than males. In the last weeks of the study, the food
    consumption of the males exceeded that of the controls by about 40%. A
    slight reduction in body-weight gain was also observed in females
    given 60 mg/kg bw per day. Males at 240 mg/kg bw per day also had an
    increased incidence of corneal opacity and evidence of mild anaemia,
    with significant reductions in erythrocyte and haemoglobin counts and
    packed cell volume.

         Changes in clinical chemistry were seen mainly in rats at 240
    mg/kg bw per day and appeared to be transient. In males, the changes
    included significantly increased aspartate aminotransferase activity
    during weeks 13 and 26, increased alkaline phosphatase activity during
    week 8, and increased blood urea nitrogen concentration during week 52
    and 78. The cholesterol concentration was significantly increased in
    all treated groups during week 52 but not at other times. Females had
    significant increases in aspartate aminotransferase activity during
    weeks 13 and 78, in alanine aminotransferase activity during week 13
    (but significant reductions in weeks 4, 52, and 78), in alkaline
    phosphatase activity in week 26, and in cholesterol concentration in
    week 8. Alkaline phosphatase activity was also increased in females
    given 60 mg/kg bw per day during week 26. Males given 60 mg/kg bw per
    day and rats of each sex given 240 mg/kg bw per day had significantly
    greater water intake than the controls. Polyuria was observed in males
    given 240 mg/kg bw per day, and a slight increase in urinary output
    was noted in females at this dose. The specific gravity of urine
    samples from the males given 240 mg/kg bw per day was consistently
    lower than that of the controls.

         At termination, the mean group kidney weight of males given 240
    mg/kg bw per day was significantly increased. Treatment-related
    microscopic changes were confined to the rats at 60 or 240 mg/kg bw
    per day and included deposition of brown pigment in macrophages and
    related cells in the liver, spleen, lymph nodes, and bone marrow, and
    cystic distension of the renal tubules and glomeruli, with dystrophic
    mineralization of the renal medulla. Muscle sections were not taken
    for microscopic examination, but evidence of increased atrophy was
    found in rats at the highest dose in muscle samples attached to the
    sternum. The NOEL for toxicity was 15 mg/kg bw per day on the basis of
    reduced body-weight gain, some clinical chemical changes,
    histopathological changes in the kidney, and skeletal muscle atrophy
    at higher doses. The incidence of mammary fibroadenomas was increased
    in females given 240 mg/kg bw per day, and many of them had multiple
    tumours. Males at this dose had an increased incidence of cutaneous
    fibromas (Brown, 1979).

         In a separate report, the original histological data from the
    study described above were re-tabulated and reanalysed. A number of
    assumptions had to be made, since it was not always clear which
    tissues had been examined from which animal, which lesions had been
    reported, and what terminology had been used. The following overall
    conclusions were drawn. Females given 240 mg/kg bw per day had a
    significantly increased incidence of multiple fibroadenomas and a
    decreased incidence of single fibroadenomas in the mammary gland as
    compared with the controls; there was no significant difference in the
    combined incidence of multiple and single fibroadenomas. Males at this
    dose had a significantly increased incidence of multiple subcutaneous
    fibromas in comparison with the controls; an apparent decrease in the
    incidence of single fibromas was not significant, and there was no
    significant difference in the combined incidence of multiple and
    single fibroadenomas. Rats of each sex given 240 mg/kg bw per day had
    a nonsignificant increase in the incidence of fibrosarcomas (Finch,
    1993).

    2.2.4  Genotoxicity

         The results of studies of the genotoxicity of imidocarb are
    summarized in Table 3. The concentrations and doses are expressed as
    imidocarb base, except when stated otherwise. Negative results were
    obtained in asays for gene mutation in bacteria and in mammalian cells
     in vitro. In two separate experiments, imidocarb induced polyploidy
    in human lymphocytes  in vitro; however, there was no induction of
    aneuploidy. Negative results were obtained in a test for micronucleus
    formation in mouse bone marrow, in a metaphase analysis in bone marrow
    of rats  in vivo, and in an inadequately conducted assay for dominant
    lethal mutation.

    2.2.5  Reproductive toxicity

          (i)  Multigeneration reproductive toxicity

          Rats

         A multigeneration study was carried out in rats as part of a
    larger study designed to investigate all aspects of reproduction,
    including teratogenicity, and to provide weanling rats for a two-year
    study. Groups of 15 Sprague-Dawley rats of each sex were maintained on
    diets containing 0, 630, 1900, or 9000 mg/kg imidocarb dipropionate
    (presumably expressed as salt, although this is not clear from the
    report) for 60 days before mating. The diets were stated to provide an
    equivalent of 0, 45, 130, or 760 mg/kg bw of imidocarb dipropionate
    per day. The numbers of pups in both the F1a and F1b litters were
    significantly reduced at the highest dose; thus, only three females
    receiving 9000 mg/kg produced F1a litters. There was a similar
    reduction in the F1b litters receiving the intermediate dose. F2
    litters were bred only from the animals at the low dose, and the study
    was terminated early owing to failure of the temperature control
    mechanism in the animal rooms. No firm conclusions could be drawn from
    this study (Hart, 1974b).


        Table 3. Results of genotoxicity studies on imidocarb

                                                                                                                                       

    End-point       Test object                       Concentration                        S9   Result      GLP    Reference
                                                                                                                                       

    In vitro
    Gene mutation   S. typhimurium TA1535, TA1537,    < 1000 g/plate                      +    Negativea   No     Moore (1997)
                    TA1538, TA98, TA100               < 250 g/plate                       -    Negativea

    Gene mutation   S. typhimurium TA1535, TA1537,    0.2-1000 g/plate                    +    Negativea   No     Moore & Chatfield
                    TA1538, TA98, TA100                                                    -    Negativea          (1983)

    Gene mutation   S. typhimurium TA98, TA100        4-2650 g/plate                      +    Negative    Yes    Tait & Clare
                    TA1535, TA1537, E. coli WP2       33-530 g/plate                      -    Negativeb          (1991a)
                    pKM101, WP2uvrA- pKM101           53-265 g/plate
                                                      (with strain WP2uvrA- pKM101 only)

    Gene mutation   hprt locus of L5178Y mouse        0.55-1749 g/ml                      +    Negative    Yes    Tait & Clare
                    lymphoma cells                    54.7-1749 g/ml                      -    Negative           (1991b)

    Chromosomal     Human peripheral blood            3.5-35 g/ml (as imidocarb           -    Negative    No     Whitaker &
    aberration      lumphocytes                       dipropionate); higher doses were                             Bonhoff (1983)
                                                      toxic

    Chromosomal     Human peripheral blood            20 h -S9; 144-294 g/ml;             +    Positivec   Yes    Tait & McEnaney
    aberration      lymphocytes                       20 h +S9; 857-1749 g/ml (expt 1)                            (1991)
                                                      20 h -S9; 235-367 g/ml;
                                                      20 h + S9; 1119-1749 g/ml;
                                                      44 h -S9; 235 g/ml; 44 h +S9;
                                                      1119 g/ml (expt 2)
                                                      44 h + S9; 366.8-1119 g/ml (expt 3)

    Micronucleus    Human peripheral blood            366.8-1120 g/ml (for frequency of   +    Negativee   Yes    Marshall (1993)
    formation       lymphocytes                       micronuclei)
                                                      895.5 g/ml (for polyploidy)
                                                                                                                                       

    Table 3. (continued)

                                                                                                                                       
    End-point       Test object                       Concentration                        S9   Result      GLP    Reference
                                                                                                                                       
    Host-mediated   Male ICR mice (10/group)          Five daily oral doses of 15, 45 or        Negative    No     Sibinovic (1986)
    assay           S. typhimurium TA1530, G-46       150 mg/kg bw; test organism given
                                                      intraperitoneally 30 min after last 
                                                      dosea

    In vivo
    Bone marrow     Sprague-Dawley rats (5/dose);     Five consecutive daily                    Negative    No     Fabrizio (1986)
    metaphase       bone marrow harvested 5 days      oral doses of 10, 30, or
    analysis        after treatment with imidocarb;   100 mg/kg bwa
                    40-50 metaphase spreads/rat
                    analysed

    Micronucleus    CD-1 mouse (5/sex per dose);      Single intraperitoneal injection of       Negative    Yes    Tait & Marshall
    formation       marrow harvested 24, 48, 72h      8, 5, 17, or 34 mg/kg bw                                     (1991)
                    after treatment

    Dominant        Male Evans mice                   Five daily intramuscular injections       Negatived   No     Harper et al.
    lethal                                            of 4 or 16 mg/kg bw followed by a                            (1977)
    mutation                                          six-week mating schedule
                                                                                                                                       

    S9, 9000  g fraction of rat liver; GLP, conformity with good laboratory practice
    a No information on whether concentrations or doses reported in terms of imidocarb base or diproprionate salt
    b Although there was a statistically significant increase in the number of revertants with strain WP2uvrA- pKM101 in the presence
      of S9, the increase was less than double the value for the solvent control, there was no concentration-related response, and the
      values were within the range for contemporary historical controls.
    c Treatment in the absence of S9 resulted in significant increases in the frequencies of cells with structural aberrations; it was 
      stated that the frequencies were within the range in historical controls, but the Committee did not consider the historical
      controls to be appropriate.  Statistically significant increases in the frequency of cells with numerical aberrations were observed
      in cultures treated in the presence of S9 and sampled at 44 h, in both experiments 2 and 3.
    d Although there were statistically significant increases in the percentage of dead implants in the group receiving 6 mg/kg bw during
      week 2, there was no dose-response relationship, and the incidence in the control group was unusually low.  The treatment and mating 
      schedules used in this study did not comply with modern guidelines.
    e There was no increase in the incidence of micronuclei at any concentration; however, an increased frequency of polypoid cells was
      observed at the single concentration tested.
    

         In another study that did not comply with GLP, groups of 20
    Wistar rats of each sex were fed diets calculated to provide 0, 15,
    45, or 135 mg/kg bw per day imidocarb dipropionate. Treatment
    commenced when the rats were six weeks old, 60 days before the first
    mating, and continued throughout the breeding of three succesive
    generations. At 21 days  post partum, the F1a, F2a, and F2b
    litters were killed and examined internally. The F1b and F2b
    litters were mated to provide the subsequent generations. The F3b
    fetuses were removed on day 20 of gestation and examined for
    malformations.

          During the premating period, females of the parental generation
    showed a small but dose-related decrease in body-weight gain; there
    were no clear dose-related effects on body weight in subsequent
    generations. The numbers of live births among females receiving 135
    mg/kg bw per day were reduced after the first mating of the F0
    generation, and the numbers of dead or missing fetuses were increased.
    A similar trend was observed after the first mating of the F1
    generation. Maternal body-weight gain was reduced on day 17 of
    gestation after the second mating of the F1 generation. No evidence
    of teratogenicity was found on examination of the F3b fetuses;
    however, there was a small, nonsignificant increase in the incidence
    of fetuses with bifid sternebrae. The NOEL was 45 mg/kg bw per day for
    both fetal toxicity and maternal toxicity (James, 1977).

          Dogs

         Five female dogs were given subcutaneous injections of 14 mg/kg
    bw imidocarb dipropionate (expressed as free base) on the first day of
    pro-oestrus and again immediately after successful mating. Six
    untreated dogs were used as controls. The dogs were allowed to litter
    naturally. After the first whelping, all the treated dogs were dosed
    and bred a second time. There were no signs of toxicity and no effects
    on on fertility, gestation, or appearance of pups (Szot, 1972).

          (ii)  Developmental toxicity

          Rats

         Teratogenicity was studied in rats within a multigeneration
    study, which did not comply with the principles of GLP. Groups of 15
    female rats were fed imidocarb dipropionate continuously in the diet
    for 60 days before mating, achieving intakes of about 0, 47, 140, or
    760 mg/kg bw per day. They were killed on day 19 of gestation, and the
    uterine contents were examined. Two-thirds of the fetuses were then
    processed for staining with Alizarin Red S for skeletal evaluation,
    and the remaining one-third were fixed in Bouin's solution and
    sectioned for evaluation of visceral abnormalities.

         Maternal body-weight gain was significantly reduced at the doses
    of 140 and 760 mg/kg bw per day and the incidence of resorptions was
    significant-ly increased in those at 760 mg/kg bw per day with a
    consequent reduction in the numbers of live fetuses. Animals at 140

    mg/kg bw per day also showed a small increase in the resorption rate.
    Fetal body weight and length were reduced at 760 mg/kg bw per day.
    There was no evidence of teratogenicity at any dose (Hart, 1973b).

         In a second study, which was not carried out in compliance with
    the principles of GLP, groups of 27-31 mated female Wistar rats were
    given daily oral doses of 0 (untreated), 0 (distilled water, solvent),
    19, 76, or 300 mg/kg bw imidocarb dipropionate (expressed as base) by
    gavage on days 6-16 of gestation. Groups of 20-25 dams were killed on
    day 20 of gestation and the uterine contents examined. One-third of
    the fetuses were examined by open dissection, one-third were processed
    by Wilson's section technique for examination of thick serial
    sections, and one-third were processed for staining with Alizarin Red
    S for skeletal evaluation. The remaining six dams in each group were
    allowed to deliver naturally and rear the offspring to weaning on day
    21  post partum.

         Maternal body-weight gain was significantly reduced during
    treatment with 300 mg/kg bw per day. There was no evidence of
    teratogenicity, but the numbers of fetuses with bifid or H-shaped
    sternebrae were increased at doses of 76 and 300 mg/kg bw per day.
    There were no treatment-related effects on the growth or survival of
    the offspring  post partum. The NOEL for fetotoxicity was 19 mg/kg bw
    per day (James, 1976a).

          Rabbits

         Groups of 16-27 female Dutch rabbits were given daily doses of 0
    (water), 20, 80, or 320 mg/kg bw per day of imidocarb dipropionate
    (doses expressed as base) by oral gavage on days 8-19 of gestation.
    The study was not carried out in compliance with the principles of
    GLP. All 16 rabbits given 320 mg/kg bw per day and one out of 27 given
    80 mg/kg bw per day died. The remaining dams showed signs of stress
    (nervous behaviour, diarrhoea, weight loss), which were attributed to
    their close proximity to a dog colony. Five to six dams in each group
    were allowed to deliver naturally, but most of the dams killed their
    offspring. There was no evidence of teratogenicity. The study was
    inadequate for establishing a NOEL (James, 1976b).

         In another study, which was not carried out in accordance with
    the principles of GLP, groups of 10-20 female New Zealand white
    rabbits were given doses of 0 (distilled water), 5, 10, 20, 60, or 180
    mg/kg bw per day of imidocarb dipropionate by oral gavage on days 6-18
    of gestation. The surviving does were killed on day 29 of gestation
    and the uterine contents examined. The general appearance of each
    fetus and the internal organs of the neck, thorax, and abdomen were
    examined grossly. All fetuses were then eviscerated, preserved, and
    stained for skeletal examination.

         All 10 does given 180 mg/kg bw per day and 12 out of 15 given
    60 mg/kg bw per day died. The does in these groups displayed signs of
    gastrointestinal disturbance, salivation, nasal exudation, and weight
    loss before death. The incidence of post-implantation loss was

    increased in animals at 60 mg/kg bw per day, and only 12 fetuses
    remained for examination. Fetal weights appeared to be reduced, and
    the incidence of delayed ossification appeared to be increased. There
    was no evidence of teratogenicity at any dose. The NOEL for both
    maternal toxicity and fetotoxicity was 20 mg/kg bw per day (Tesh et
    al., 1977).

    2.2.6  Special studies to investigate serum prolactin concentrations

         A study which did not comply with GLP was carried out to
    investigate the mechanism of the induction of mammary tumours in the
    two-year study in rats. Groups of 10 male Wistar rats were fed diets
    calculated to provide 0, 15, 60, or 240 mg/kg bw per day of imidocarb
    (as base) for 28 days. Another group was given 160 mg/kg bw per day of
    sulpiride. Serum prolactin concentrations were measured before
    treatment and 2, 5, 8, 14, and 22 days after the first dose. The mean
    prolactin concentrations were significantly  (p < 0.001) increased
    in the group receiving sulpiride from day 2 onwards and were slightly
    increased in the group given 240 mg/kg bw per day imidocarb, although
    they never approached the values found in the group given sulpiride
    (Clampitt et al., 1982). 

    2.2.7  Special studies on microbiological activity

         In a study that did not conform to GLP, MIC values  in vitro 
    were determined for imidocarb against 20 bacterial isolates
    representing seven genera. MIC values > 16 g/ml were obtained for 18
    isolates, and values of 4 and 8 g/ml were obtained for two strains of
     Pasteurella (Darby & Pelham, 1989).

    2.2.8  Special studies on pharmacodynamic effects

         It is generally accepted in the published literature that
    imidocarb has anticholinesterase activity and that the toxic signs
    observed after treatment can be alleviated with atropine (Ali et al.,
    1985; Michell et al., 1986; McDougald & Roberson, 1988). The
    pharmacodynamic effects of imidocarb were investigated in a screening
    study in which mice were given single subcutaneous doses of the
    dihydrochloride salt. Myosis was observed at 50 mg/kg bw, but
    mydriasis occurred at 150 mg/kg bw (Green, 1966). In another study,
    cardiovascular and neuromuscular effects were observed after
    intravenous administration of imidocarb dihydrochloride to
    anaesthetized cats and dogs, which were attributed in part to the
    anticholinesterase effect. No effect on the pupil was observed after
    instillation of a solution of 10 mg/ml imidocarb dihydrochloride into
    a cat's eye (Green & Hughes, 1969). No conclusions could be drawn
    about anticholinesterase potency from these data.

         The mode of action of imidocarb as an antiprotozoal agent is
    uncertain, although two mechanisms have been proposed:

    *    As the effect of imidocarb on  Trypanosoma brucei is antagonized
         by excess polyamines, it is has been suggested that imidocarb
         interferes with their production and/or use (Bacchi et al.,
         1981).

    *    Imidocarb blocks the entry of inositol into erythrocytes
         containing  Babesia, resulting in 'starvation' of the parasite
         (McHardy  et al., 1986).

    2.3  Observations in humans

         It is believed that imidocarb has been used occasionally in human
    medicine, but no details of doses or adverse effects were available to
    the Committee.

    3.  COMMENTS

         The Committee considered data from studies of the
    pharmacokinetics, metabolism, acute, and short-term toxicity,
    long-term toxicity and carcino-genicity, reproductive toxicity and
    genotoxicity of imidocarb and some special studies. Most of the
    studies were carried out with the dipropionate salt, and the doses
    used were expressed as imidocarb base. Except for some of the assays
    for genotoxicity, the studies were not carried out to contemporary
    standards for study protocol and conduct but were reported in
    sufficient detail and were considered adequate for assessment.

         The pharmacokinetics of imidocarb was investigated in mice, rats,
    dogs, monkeys, and cattle. The dipropionate and dihydrochloride salts
    of imidocarb appeared to be poorly absorbed after oral administration
    to rats, but the extent of the oral bioavailability could not be
    estimated from the data available. In cattle dosed subcutaneously,
    imidocarb was bound to plasma proteins. The drug was excreted in both
    urine and the faeces for several days in rodents and for at least 28
    days in cattle.

         In mice dosed intravenously with radiolabelled imidocarb and
    killed 3.5 h later, more than 90% of the residues in liver and kidney
    were unmetabolized imidocarb. The parent compound also accounted for
    95% of the radiolabelled material in mouse urine. In cattle dosed
    subcutaneously with radiolabelled imidocarb, the parent compound
    accounted for most of the residues in urine and faeces and 70-90% of
    the residues in edible tissues and milk. No evidence of metabolism was
    found in a study of bovine liver slices, isolated hepatocytes, or
    microsomal fractions  in vitro.

         Imidocarb dipropionate is moderately hazardous, with oral LD50
    values in the range of 650-720 mg/kg bw in mice and 450-1200 mg/kg bw
    in rats. The signs were generally consistent with anticholinesterase
    activity.

         Serum cholinesterase activity was depressed in a dose-related
    manner in goats given single intramuscular doses of 12-24 mg/kg bw.
    Whole-blood cholinesterase activity was decreased in calves given
    single intramuscular injections of 3.3 mg/kg bw.

         When rats were given daily oral doses of 0, 125, 250, 500, 750,
    or 1500 mg/kg bw per day of imidocarb dihydrochloride for three
    months, all rats at the highest dose died. Cloudy swelling in the
    liver was observed in rats given 125 and 250 mg/kg bw per day.
    Histopathological examinations were not performed on rats at higher
    doses. No NOEL was identified.

         In a study conducted to identify appropriate doses for a
    long-term study of toxicity, rats were fed diets calculated to provide
    doses of imidocarb dipropionate equal to 0, 26, 75, or 420 mg/kg bw
    per day for 90 days. Body-weight gain was reduced in animals of each
    sex given 420 mg/kg bw per day. Acetylcholinesterase activity,
    measured in one-half of the brain from each of 10 rats given 420 mg/kg
    bw per day and killed after 7 and 13 weeks, was not significantly
    different from that in controls. Pathological changes attributable to
    treatment were limited to mild stasis of the bile in the canaliculi of
    the liver in one male and four females given 420 mg/kg bw per day. The
    NOEL was 75 mg/kg bw per day on the basis of reduced body-weight gain
    and hepatic toxicity at higher doses.

         Groups of four dogs of each sex per dose were given oral doses of
    0, 5, 20, or 80 mg/kg bw per day imidocarb dipropionate in gelatin
    capsules for 90 days. The signs of toxicity in the dogs given 80 mg/kg
    bw per day included recumbency, salivation, muscle fasciculation,
    ataxia, and splayed legs. All males and two of four females given this
    dose died or were killed. Blood eosinophilia was also observed at 80
    mg/kg bw per day, with increased serum alanine aminotransferase and
    aspartate aminotransferase activity and increased bilirubin
    concentration. Similar but less severe changes were observed in the
    dogs given 20 mg/kg bw per day. The weights of the kidney, thyroid,
    and adrenal glands were increased in animals at 80 mg/kg bw per day,
    and histopathological changes were found in a range of tissues. In the
    kidney, these included fatty changes in the thick section of the loop
    of Henle and the distal convoluted tubules. The liver showed
    haemorrhagic necrosis, fatty change, and microgranularity or
    vacuolation of hepatocytes. Similar but less severe hepatocellular
    changes were found in the livers of dogs given 20 mg/kg bw per day.
    The NOEL was 5 mg/kg bw per day on the basis of minor changes in
    haematological and clinical chemical parameters and hepatocellular
    changes at higher doses.

         In a long-term study of toxicity and carcinogenicity, rats were
    fed diets calculated to provide intakes of 0, 15, 60, or 240 mg/kg bw
    per day of imidocarb as dipropionate for two years. Survival was
    adversely affected at the highest dose. Body-weight gain was
    significantly reduced in animals of each sex given 240 mg/kg bw per
    day and was slightly reduced in females given 60 mg/kg bw per day.
    Males at 240 mg/kg bw per day showed evidence of anaemia. Changes in
    clinical chemical parameters were transient and occurred mainly in the
    animals given the highest dose. Rats given 60 or 240 mg/kg bw per day
    drank considerably more water than the controls, and polyuria was
    observed in males at the highest dose. At termination, the weights of
    the kidneys of males given 240 mg/kg bw per day were significantly
    increased. Dose-related histopathological changes were observed at 60
    and 240 mg/kg bw per day, which included cystic distension of the
    renal tubules and glomeruli and dystrophic mineralization in the renal
    medulla. The NOEL for toxicity was 15 mg/kg bw per day on the basis of
    reduced body-weight gain, changes in some clinical chemical
    parameters, and histopathological changes in the kidney. All animals
    were examined grossly, and all gross lesions were examined
    microscopically; however, comprehensive pathological examinations was
    made on only 10 control rats of each sex and 19 females and four males
    at the highest dose at termination of the study. A limited range of
    tissues from the other animals was examined, and mammary glands were
    examined only when a gross lesion was found. At the highest dose, a
    significantly increased incidence of multiple fibroadenomas of the
    mammary gland was found in females and of multiple subcutaneous
    fibromas in males. Because of the excessive toxicity at this dose, the
    poor survival, and limited histopathological examination, the
    significance of these findings could not be evaluated. The incidences
    of tumour at other sites were not increased.

         The genotoxic properties of imidocarb dipropionate were
    investigated in a range of assays  in vitro and  in vivo. Negative
    results were obtained for gene mutation in  Salmonella typhimurium 
    and in mammalian cells  in vitro and in a host-mediated assay in male
    mice. In two separate experiments, imidocarb induced polyploidy in
    human peripheral blood lymphocytes  in vitro in the presence of
    metabolic activation; however, aneuploidy was not induced. Micronuclei
    were not induced in mouse bone marrow, and no chromosomal aberrations
    were induced in rat bone marrow  in vivo. Dominant lethal mutations
    were not found in mice, although the dosing and mating schedules used
    were not in accordance with contemporary guidelines. The Committee
    concluded that imidocarb is unlikely to be genotoxic.  In a
    three-generation study of reproductive toxicity, rats were fed diets
    calculated to provide intakes of 0, 15, 45, or 135 mg/kg bw per day
    imidocarb as dipropionate. The body-weight gain of dams at 135 mg/kg
    bw per day was decreased, and the number of live births was reduced.
    The NOEL was 45 mg/kg bw per day for both fetal toxicity and maternal
    toxicity.

         In a study of developmental toxicity in rats, there was no
    evidence of teratogenicity after administration of imidocarb
    dipropionate by gavage at doses of 0, 19, 76, or 300 mg/kg bw per day
    on days 616 of gestation. Groups of 20-25 dams were killed on day 20
    of gestation and the uterine contents examined; the remaining six dams
    in each group were allowed to deliver naturally and rear the
    offspring. Maternal body-weight gain was reduced at 300 mg/kg bw per
    day. The number of fetuses with bifid or H-shaped sternebrae was
    increased in groups of rats receiving 76 or 300 mg/kg bw per day.
    There were no treatment-related effects on the growth or survival of
    the offspring  post partum. The NOEL for fetotoxicity was 19 mg/kg bw
    per day. In a study of developmental toxicity in rabbits, there was no
    evidence of teratogenicity after administration of 0, 5, 10, 20, 60,
    or 180 mg/kg bw per day of imidocarb as dipropionate by gavage on days
    618 of gestation. Severe maternal toxicity was observed at 60 and 180
    mg/kg bw per day, and all dams given 180 mg/kg bw per day and 12 of 15
    given 60 mg/kg bw per day died. The frequency of post-implantation
    losses was increased and fetal weights were reduced in the group given
    60 mg/kg bw per day. The NOEL for maternal and fetotoxicity was 20
    mg/kg bw per day.

    4.  EVALUATION

         An ADI of 0-10 g/kg bw per day was established on the basis of
    the NOEL of 5 mg/kg bw per day in the 90-day study in dogs. A safety
    factor of 500 was used to compensate for the limited pathological and
    clinical chemical investigations in this study, the absence of
    information about potential inhibition of erythrocyte and regional
    brain acetylcholinesterase activity in this species, the lack of data
    on neurotoxicity, and the limited data on carcinogenic potential.

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    Follefant, R & Green, A.F. (1971b) Imidocarb i.e. 4A65. Comparative
    toxicity in mice. Unpublished report No BPHR/71/79 from Wellcome
    Research Laboratories, Beckenham, Kent, United Kingdom. Submitted to
    WHO by Mallinckrodt, Harefield, Uxbridge, Middlesex, United Kingdom.

    Green, A.F. (1966) Preliminary assessment of acute pharmacodynamic
    effects. Unpublished report No.BPHR 66-58 from Wellcome Research
    Laboratories, Beckenham, Kent, United Kingdom. Submitted to WHO by
    Mallinckrodt, Harefield, Uxbridge, Middlesex, United Kingdom.

    Green, A.F. & Hughes, R. (1969) Pharmacodynamics and acute toxicity.
    Unpublished report No. BPHR 69-8 from Wellcome Research Laboratories,
    Beckenham, Kent, United Kingdom. Submitted to WHO by Mallinckrodt,
    Harefield, Uxbridge, Middlesex, United Kingdom.

    Harper, D.W. & James, J.A. (1977) Imidocarb dipropionate: Multiple
    dosing intramuscular toxicity in male mice (range finder study for
    dominant lethal test). Unpublished report No. HZIG 77-1 from Wellcome
    Research Laboratories, Berkhamsted and Beckenham, United Kingdom.
    Submitted to WHO by Mallinckrodt, Harefield, Uxbridge, Middlesex,
    United Kingdom.

    Harper, D.W., Piercy, D.W.T. & James, J.A. (1977a) Imidocarb
    dipropionate: Acute oral toxicity in the female rat (10% solution).
    Unpublished report No. HZIG 77/2 from Wellcome Research & Development,
    Berkhamsted Hill, United Kingdom. Submitted to WHO by Mallinckrodt,
    Harefield, Uxbridge, Middlesex, United Kingdom.

    Harper, D.W., Piercy, D.W.T. & James, J.A. (1977b) Imidocarb
    dipropionate: Acute oral toxicity in the male rat (10% solution).
    Unpublished report No. HZIG 77/3 from Wellcome Research & Development,
    Berkhamsted Hill, United Kingdom. Submitted to WHO by Mallinckrodt,
    Harefield, Uxbridge, Middlesex, United Kingdom.

    Harper, D.W., Piercy, D.W.T. & James, J.A. (1977c) Imidocarb
    dipropionate: Acute oral LD50 in the female rat (30% solution).
    Unpublished report No. HZIG 77/5 from Wellcome Research & Development,
    Berkhamsted Hill, United Kingdom. Submitted to WHO by Mallinckrodt,
    Harefield, Uxbridge, Middlesex, United Kingdom.

    Harper, D.W., Piercy, D.W.T. & James, J.A. (1977d) Imidocarb
    dipropionate: Acute oral LD50 in the male rat (30% solution).
    Unpublished report No. HZIG 77/6 from Wellcome Research & Development,
    Berkhamsted Hill, United Kingdom. Submitted to WHO by Mallinckrodt,
    Harefield, Uxbridge, Middlesex, United Kingdom.

    Harper, D.W. James, J.A. & Parker, M.J. (1977e) Imidocarb
    dipropionate: Dominant lethal study in male mice. Unpublished report
    No. HZIG 77-4 from Wellcome Research Laboratories, Beckenham, United
    Kingdom. Submitted to WHO by Mallinckrodt, Harefield, Uxbridge,
    Middlesex, United Kingdom.

    Hart, E.R. (1973a) 90-day feeding study in rats. Imidicarb
    dipropionate. Revised final report. Unpublished report No. XZIG 86-4
    from Litton Bionetics, Inc., Bethesda, Maryland, USA. Submitted to WHO
    by Mallinckrodt, Harefield, Uxbridge, Middlesex, United Kingdom.

    Hart, E.R. (1973b) Teratology phase. Imidocarb dipropionate. Final
    report. Unpublished report No. XZIG 86-7 from Litton Bionetics, Inc.,
    Bethesda, Maryland, USA.  Submitted to WHO by Mallinkrodt.

    Hart, E.R. (1974a) Chronic toxicity phase. Imidicarb dipropionate.
    Final report. Unpublished report No. XZIG 86-5 from Litton Bionetics,
    Inc., Bethesda, Maryland, USA. Submitted to WHO by Mallinckrodt,
    Harefield, Uxbridge, Middlesex, United Kingdom.

    Hart, E.R. (1974b) Reproduction phase. Imidocarb dipropionate. Final
    report. Unpublished report No. XZIG 86-9 from Litton Bionetics Inc.,
    Bethesda, Maryland, USA. Submitted to WHO by Mallinckrodt, Harefield,
    Uxbridge, Middlesex, United Kingdom.

    James, D.A. (1976a) Foetal toxicity study of 4A65 (imidocarb
    dipropionate) in rats. Unpublished report No. BPAT 76/9 from Wellcome
    Research Laboratories, Beckenham, Kent, UNited Kingdom. Submitted to
    WHO by Mallinckrodt, Harefield, Uxbridge, Middlesex, United Kingdom.

    James, D.A. (1976b) An account of attempted foetal toxicity study of
    4A65 (imidocarb dipropionate) in the rabbit. Unpublished report No.
    BPAT 76/20 from Wellcome Research Laboratories, Beckenham, Kent,
    United Kingdom. Submitted to WHO by Mallinckrodt, Harefield, Uxbridge,
    Middlesex, United Kingdom.

    James, D.A. (1977) Multigeneration reproduction study of 4A65
    (imidocarb dipropionate) in the rat. Unpublished report No. BPAT 77/24
    from Wellcome Research Laboratories, Beckenham, Kent, United Kingdom.
    Submitted to WHO by Mallinckrodt, Harefield, Uxbridge, Middlesex,
    United Kingdom.

    Marshall, R.R. (1993) Study to evaluate the clastogenic potential of
    imidocarb by its effects on the frequency of micronuclei in cultured
    human peripheral blood lymphocytes. Unpublished report No. R-93-015
    from Hazleton Microtest, Harrogate, United Kingdom. Submitted to WHO
    by Mallinckrodt, Harefield, Uxbridge, Middlesex, United Kingdom.

    McDougald, L.R. & Roberson, E.L. (1988) Antiprotozoan drugs. In:
     Veterinary Pharmacology and Therapeutics, 6th Ed., Ames, Iowa State
    University Press, pp. 950-968.

    McHardy, N., Woollon, R.M., Clampitt, R.B., James, J.A. & Crawley,
    R.J. (1986) Efficacy, toxicity and metabolism of imidocarb
    dipropionate in the treatment of  Babesia ovis infection in sheep.
     Res. Vet. Sci., 41, 14-20.

    Michell, A.R., White, D.G., Higgins, A.J., Moss, P. & Lees, P. (1986)
    Effect of induced hypomagnesemia on the toxicity of imidocarb in
    calves.  Res. Vet. Sci., 40, 264-270.

    Moore, W.B. (1977) Mutagenic activity of imidocarb dipropionate.
    Unpublished report No. BEMU/77/3 from Wellcome Research Laboratories,
    Beckenham, United Kingdom. Submitted to WHO by Mallinckrodt,
    Harefield, Uxbridge, Middlesex, United Kingdom.

    Moore, W.B. & Chatfield, S.N. (1983) Mutagenicity: Evaluation of
    imidocarb dipropionate using a method based on the Yahagi modification
    of the Ames Salmonella/microsome incorporation test. Unpublished
    report No. BEMU/83/1 from Wellcome Research Laboratories, Beckenham,
    United Kingdom. Submitted to WHO by Mallinckrodt, Harefield, Uxbridge,
    Middlesex, United Kingdom.

    Nimmo-Smith, R.H. (1968) Distribution, excretion and tissue levels of
    compound 4A65 (HR 2073) in the rat. Unpublished report No. 3BT68 from
    Wellcome Research Laboratories, Berkhamsted, United Kingdom. Submitted
    to WHO by Mallinckrodt, Harefield, Uxbridge, Middlesex, United
    Kingdom.

    Piercy, D.W.T. & James, J.A. (1976) Imidocarb dipropionate oral LD50
    in rabbits. Unpublished report No. HZIG 76-1 from Wellcome Research &
    Development, Berkhamsted Hill, United Kingdom. Submitted to WHO by
    Mallinckrodt, Harefield, Uxbridge, Middlesex, United Kingdom.

    Reynolds, J., Clampitt, R.B., Piercy, D.W.T., James, J.A. & Skarpa, M.
    (1977) Subacute 90 day oral toxicity of imidocarb dipropionate in the
    dog. Unpublished report No. HZIG 77-11 from Wellcome Research
    Laboratories, Berkhamsted and Beckenham, United Kingdom. Submitted to
    WHO by Mallinckrodt, Harefield, Uxbridge, Middlesex, United Kingdom.

    Salam, A.A. & Baggot, J.D. (1983) Adverse effects of imidocarb
    dipropionate (Imizol) in a dog.  J. Vet. Pharmacol. Ther., 5,
    131-135.

    Sibinovic, K.H. (1986) In vitro and subacute in vivo host-mediated
    assay for mutagenesis. Unpublished report No. XZIG from Litton
    Bionetics, Inc., Bethesda, Maryland, USA. Submitted to WHO by
    Mallinckrodt, Harefield, Uxbridge, Middlesex, United Kingdom.

    Szot, R.J. (1973a) Oral and intravenous acute toxicity studies of
    imidocarb dipropionate (4A65) in mice and rats. Unpublished report no.
    T-TEP-73-4 from Department of Toxicology-Experimental Pathology,
    Research Triangle Park, North Carolina, USA. Submitted to WHO by
    Mallinckrodt, Harefield, Uxbridge, Middlesex, United Kingdom.

    Szot, R.J. (1972b) Fertility study in dogs given imidocarb
    dipropionate. Unpublished report No. TTEP-72-11 from the Department of
    Toxicology - Experimental Pathology, Research Triangle Park, North
    Carolina, USA. Submitted to WHO by Mallinckrodt, Harefield, Uxbridge,
    Middlesex, United Kingdom.

    Tait, A.J. & Clare, C.B. (1991a) Study to evaluate the ability of
    imidocarb to induce mutation in four histidine-requiring strains of
     Salmonella typhimurium and two tryptophan requiring strains of
     E. coli. Unpublished report No. RRS-91-22 from Hazleton Microtest,
    York, United Kingdom. Submitted to WHO by Mallinckrodt, Harefield,
    Uxbridge, Middlesex, United Kingdom.

    Tait, A.J. & Clare, C.B. (1991b) Study to determine the ability of
    imidocarb to induce mutations to 6-thioguanine resistance in mouse
    lymphoma L5179Y cells using a fluctuation assay. Unpublished report
    No. RRS-91-15 from Hazleton Microtest, York, United Kingdom. Submitted
    to WHO by Mallinckrodt, Harefield, Uxbridge, Middlesex, United
    Kingdom.

    Tait, A.J. & Marshall, R.R. (1991) Study to evaluate the potential of
    imidocarb to induce micronuclei in the polychromatic erythrocytes of
    CD-1 mice. Unpublished report No. RRS-91-23 from Hazleton Microtest,
    York, United Kingdom. Submitted to WHO by Mallinckrodt, Harefield,
    Uxbridge, Middlesex, United Kingdom.

    Tait, A.J. & McEnaney, S. (1991) Study to evaluate the chromosome
    damaging potential of imidocarb by its effect on cultured human
    lymphocytes using an  in vitro cytogenetics assay. Unpublished report
    No. RRS-91-32 from Hazleton Microtest, York, United Kingdom. Submitted
    to WHO by Mallinckrodt, Harefield, Uxbridge, Middlesex, United
    Kingdom.

    Tesh, J.M., Ross, F.W. & Tesh, S.A. (1977) 4A: Effects of oral
    administration upon pregnancy in the rabbit. Unpublished report No.
    77/WRL2/109 from Life Science Research, Stock, Essex, United Kingdom.
    Submitted to WHO by Mallinckrodt, Harefield, Uxbridge, Middlesex,
    United Kingdom.

    Thomson, P.M. (1975a) Preliminary study of oral imidocarb dipropionate
    to reveal its retention in the rat. Unpublished report No. BPAT75/17
    from Wellcome Research Laboratories, Berkhamsted, United Kingdom.
    Submitted to WHO by Mallinckrodt, Harefield, Uxbridge, Middlesex,
    United Kingdom.

    Thomson, P.M. (1975b) Preliminary study of oral imidocarb dipropionate
    to reveal its retention in the monkey. Unpublished report No.
    BPAT75/18 from Wellcome Research Laboratories, Berkhamsted, United
    Kingdom. Submitted to WHO by Mallinckrodt, Harefield, Uxbridge,
    Middlesex, United Kingdom.

    Wander, A. (1968a) Distribution and excretion of (14C) labelled HR
    2073 after intravenous administration of a single dose (1 mg/kg) in
    the mouse. Translation of unpublished report No. 94/2555. Submitted to
    WHO by Mallinckrodt, Harefield, Uxbridge, Middlesex, United Kingdom.

    Wander, A. (1968b) Investigation of the activity in the urine, liver,
    gall bladder and kidneys of the mouse after intravenous administration
    of a single dose of HR 2073 C-14. Translation of unpublished report
    No. 94/2554. Submitted to WHO by Mallinckrodt, Harefield, Uxbridge,
    Middlesex, United Kingdom.

    Whitaker, A.M. & Bonhoff, A.J. (1983) Cytogenetic study of the effect
    of imidocarb dipropionate (3 ',3 '-di(2-imidazolin-2-yl)carbanilide
    dipropionate) on peripheral human lymphocytes  in vitro. Unpublished
    report No. BNCD/83/7 from Wellcome Biotechnology Ltd, United Kingdom.
    Submitted to WHO by Mallinckrodt, Harefield, Uxbridge, Middlesex,
    United Kingdom.
    


    See Also:
       Toxicological Abbreviations
       IMIDOCARB (JECFA Evaluation)