Bitertanol was first evaluated by the 1983 JMPR which allocated a
    temporary acceptable daily intake of 0-0.005 mg/kg bw and required, by
    1987, metabolism studies to clarify the metabolic pathway of
    bitertanol in mammals, an oral toxicity study in the dog with minimum
    duration of one year and a chronic toxicity and carcinogenicity study
    in rats at appropriate dosage (Annex 1, WHO/FAO, 1984). Relevant data
    has been submitted for evaluation by the present Joint Meeting and is
    summarized in this monograph addendum.



    Biochemical Aspects

    Absorption, Distribution and Excretion

         Groups of 5 male and 5 female Wistar rats received either a
    single oral dose of 14C-phenyl-radiolabelled bitertanol solution in
    ethylene glycol (100 mg/kg or 100 mg/kg), a single intravenous dose
    (100 mg/kg) or 14 daily oral doses (100 mg/kg) Followed by a single
    oral dose of 14C-radiolabelled bitertanol (100 mg/kg). Urine and
    fetes were collected 6 and 24 hours after dosing and subsequently at
    24 hour intervals until sacrifice, 7 days later. Serial blood samples
    were collected during this period.

         Faecal excretion of radioactivity following intravenous
    administration indicates that biliary excretion was predominant. In
    each case 14C-radioactivity was mostly excreted in the faeces.
    Urinary excretion amounted to about 4-11% of administered dose whilst
    expired radioactivity was not detectable. Total recoveries of
    radioactivity were high, about 92-104%.

         Pharmacokinetic analysis indicated that absorption of an oral
    dose of bitertanol followed a first order pattern at the single and
    repeated low dose (100 mg/kg) but not at the higher dose (1000 mg/kg),
    suggesting saturation of absorption, distribution or elimination
    processes. The highest tissue levels detected were in liver (17.9 ppm,
    female) and kidney (5.9 ppm, male) of the high-dose groups. Tissue
    residues totalled about 0.2-0.4% of administered radioactivity (Puhl &
    Hurley, 1983).


         Alternative pathways for the metabolism of absorbed bitertanol is
    shown in the Figure. Hydroxylation of the para-position of the
    biphenyl and of a methyl group of the sec-butyl moieties gave rise to
    phenolic (1) and diol (2) metabolites. Although one diastereomer of
    the latter was detectable, it underwent oxidation to the corresponding
    butanoic acid (4) and subsequent ring hydroxylation (5). The
    para-hydroxylated diol (6) was also detected as was
    4,4-dihydroxybiophenyl (7). Other hydroxylated metabolites (8,9,10)
    were also tentatively identified (Puhl & Hurley, 1983).

    Toxicological Studies

    Special Study on Hepatotoxicity

         Groups of 10 male and 10 female Wistar rats received by gavage 0,
    30, 100 and 300 mg/kg bitertanol (95.8% purity) suspended in distilled
    water with Cremorph EL daily for 14 days. On sacrifice, blood was
    collected for detailed hematological and clinical chemistry
    examination and liver samples taken for detailed histopathology and
    enzyme studies.

         During treatment female rats of the mid- (1/10) and high-dose
    (9/10) groups exhibited hair loss. In some cases, weight loss occurred
    in mid- and high-dose rats while low-dose females had reduced
    bodyweight gain in comparison with control animals.

         Female rats had a dose-related tendency to mild thrombocytosis
    which was significant at mid- and high-doses only. Serum
    gamma-glutamyl transpeptidase and bilirubin levels were slightly
    raised in high dose female rats.

         There were no gross pathological findings at necropsy. Liver
    weights tended to be increased at mid- and high-doses, especially in
    females. Histopathology showed slight to moderate bile duct
    proliferation with peribiliary infiltration of monocytes or
    polynucleocytes at mid- and high-doses. Sometimes these changes were
    accompanied by the presence of parenchymal Councilman bodies or, more
    occasionally, mitoses. The high-dose hepatocytes were occasionally
    swollen with finely granular cytoplasm. Fatty infiltration was not

         Results of the  in vitro studies were consistent with induction
    of hepatic microsomal enzymes: cytochrome P-450 content increased in a
    dose-related manner, especially in males. Aminopyrene N-demethylase
    activity was increased in high-dose males and females and in mid-dose
    males while O-demethylase activity was increased in mid-and high-dose
    males and high-dose female rats. Hepatic triglyceride content was not
    influenced by bitertanol treatment.

         The results of this study indicate that bitertanol caused mild
    hepatotoxicity with modest induction of hepatic microspinal activity
    in rats at 100 and 300 mg/kg (Mihail & Luckhaus, 1985).

    Short-term Studies


         Groups of 4 male and 4 female beagle dogs received bitertanol
    (95-97.3% purity) for two years in the diet at 0, 10, 40 or 160 ppm.
    Although the control dogs exhibited a greater increase in bodyweight
    than did treated dogs, no relationship with bitertanol treatment was
    observed. Good nutritional status was maintained by dogs of all groups
    and there were no significant differences between groups in food and
    water consumption. No abnormalities were seen on examination or
    selected reflexes, body temperature and pulse rate. However, 3 of 8
    high-dose dogs developed bilateral cataracts. Urinalysis and
    hematological examination, conducted at approximately 3 month
    intervals, revealed no abnormalities. However, serum alanine
    amino-transferase and alkaline phosphatase were elevated at 40 and
    160 ppm.

         At necropsy, the mean liver weight of high-dose dogs only were
    markedly increased. Histological examination showed mild to moderate
    vacuolation of adrenal zona reticularis epithelia at and above 40 ppm.
    Based on this finding, the no observed effect level indicated by this
    study is 10 ppm in the diet (Hoffman & Groening, 1983).

         In another study, groups of 6 male and 6 female beagle dogs were
    fed 0, 3 and 25 ppm bitertanol (96.3-96.7%) in the diet for 12 months.
    A high dose group was maintained on a diet containing 200 ppm
    bitertanol for 20 months to permit continued ophthalmoscopic

         Treatment had no apparent effect on the dogs' behaviour,
    appearance or nutritional status. Food consumption and bodyweight gain
    were also unaffected. Physical examinations of pulse rates, body
    temperature and selected reflexes were unremarkable. Ophthalmoscopy,
    conducted at 3 monthly intervals in the control, low- and mid-dose
    groups was normal. However, in the high-dose group, one dog developed
    severe bilateral lenticular cataracts, observable from week 58. Four
    other animals exhibited slight lens opacification by week 85. In
    addition, dogs of this group also had signs of conjunctivitis with
    nasociliary discharge and incrustation. Intermittent elevation of
    serum hepatic alanine amino-transferase, glutamate dehydrogenase and
    alkaline phosphatase also occurred in the high-dose dogs. Other usual
    clinical chemical, hematological and urinalysis parameters were not
    affected by treatment in any group.

         At necropsy there was no grossly abnormal pathology. The adrenal
    weights of high-dose dogs were apparently increased in comparison to
    controls and lipoid vacuolations were observed in zona reticularis
    epithelia. The results of this study accord with the previous findings
    (Hoffman & Vogel, 1983).


         In a repeated-dose study, bitertanol (95.8% pure) in a aqueous
    suspension (0.5 ml) was applied to the intact or abraded dorsal and
    lateral skin of groups of 6 male and 6 female New Zealand rabbits 6
    hours daily 5 times per week for 3 weeks at 0, 50 and 250 mg/kg. The
    animals were inspected for signs of dermal irritation 24 hours after
    each treatment. Hematological, clinical chemical and urinalysis
    parameters were investigated at termination and the animals necropsied
    for further examination.

         Dermal exposure to bitertanol had no apparent effect on
    appearance or behaviour, bodyweight or survival of the rabbits.
    Transient erythema developed for a few days at the exposure areas,
    initially with abraded skin but later with intact skin. There was no
    effect on skin-fold thickness, hematology, clinical chemistry or
    urinalysis parameters. At necropsy, there were no gross pathological
    findings. Histopathological examination showed a slight epidermal
    thickening in exposed areas only of all treated animals. This study
    indicates that bitertanol is a weak skin irritant only.

          In vitro liver preparations showed no evidence of induction of
    microsomal N-demethylation or O-demethylation or Cytochrome P-450
    content (Heimann & Vogel, 1984).


         The 1983 JMPR requested data to clarify the metabolic pathway of
    bitertanol and additional toxicological data from a one year dog study
    and chronic and carcinogenicity studies in rats.

         In rats, bitertanol is extensively metabolized, primarily by ring
    and side chain hydroxylation, oxidation to the corresponding
    carboxylic acid and also by ether cleavage. Pharmacokinetic studies
    demonstrate that it is absorbed more completely at lower (100 mg/kg
    bw) than at higher (1000 mg/kg bw) doses. Tissue retention of absorbed
    material is low and biliary excretion predominates.

         Data evaluated by the 1983 JMPR show that short-term feeding of
    bitertanol to rats produced body weight depression and hepatotoxicity
    at 600 and 2400 ppm, (equivalent top 60-240 mg/kg bw/day). Body weight
    depression was seen in a 90-day study at 300 ppm (30 mg/kg bw/day). On
    chronic administration, bitertanol retarded the growth of rats at
    500 ppm (25-50 mg/kg bw/day).

         In view of the reduced absorption of bitertanol at high doses
    that has now been demonstrated, and because of the above mentioned
    toxicity to rats at relevant doses, the meeting considered that
    further chronic or carcinogenicity studies in rats would be unlikely
    to yield new information of toxicological significance.

         An additional study confirms that dogs are more susceptible to
    bitertanol than rats. Feeding studies of one and two years' duration
    show the formation of cataracts, conjunctivitis and mild
    hepatotoxicity, with a no-observed-adverse-effect level at 10 ppm.



          Rat:    20 ppm in the diet, equivalent to 1 mg/kg bw/day.
          Dog:    10 ppm in the diet, equivalent to 0.25 mg/kg bw/day.


         0-0.003 mg/kg bw.


         Observations in man.


    Heimann, K.G. & Vogel, O., 1984. KWG 0599 Subacute Study of Dermal
    Toxicity to Rabbits. Unpublished study from Bayer AG Institute of
    Toxicology Report No. 12571. Submitted to WHO by Bayer AG, Leverkusen,

    Hoffman, K. & Groening, P., 1983. KWG 0599/Chronic Toxicity Study on
    Dogs (2-Year Feeding Experiment). Unpublished study from Bayer AG
    Institute of Toxicology Report No. 12307. Submitted to WHO by Bayer
    AG, Leverkusen, FRG.

    Hoffman, K. & Vogel, O., 1983. KWG 0599 (Bitertanol)/Second Chronic
    Toxicity Study with Dogs on Oral Administration. Unpublished study
    from Bayer AG Institute of Toxicology Report No. 12328. Submitted to
    WHO by Bayer AG, Leverkusen, FRG.

    Mihail, F. & Luckhaus, G., 1985. KWG 0599 (Bitertanol)/Subacute Oral
    Toxicity Study with Special Attention to Effect on the Liver.
    Unpublished study from Bayer AG Institute of Toxicology Report
    No. 13230. Submitted to WHO by Bayer AG, Leverkusen, FRG.

    Puhl, R.J. & Hurley, J.B., 1983. The Absorption, Excretion and
    Metabolism of Baycor TM-phenyI-UL-C14 by Rats. Unpublished study from
    Mobay Chemical Corporation Agri. Chem. Division. Report No. 85832.
    Submitted to WHO by Bayer AG, Leverkusen, FRG.

    See Also:
       Toxicological Abbreviations
       Bitertanol (Pesticide residues in food: 1983 evaluations)
       Bitertanol (Pesticide residues in food: 1984 evaluations)
       Bitertanol (JMPR Evaluations 1998 Part II Toxicological)