SA Cage MSc M Inst Inf Sci
    SM Bradberry BSc MB MRCP
    S Meacham BSc

    National Poisons Information Service
    (Birmingham Centre),
    West Midlands Poisons Unit,
    City Hospital NHS Trust,
    Dudley Road,
    B18 7QH

    This monograph has been produced by staff of a National Poisons
    Information Service Centre in the United Kingdom.  The work was
    commissioned and funded by the UK Departments of Health, and was
    designed as a source of detailed information for use by poisons
    information centres.

    Peer review group: Directors of the UK National Poisons Information


    Toxbase summary

    Type of product



    Dermal and inhalational exposures are associated usually with no or
    only mild adverse effects. Following substantial ingestion, patients
    may develop coma, convulsions and severe muscle fasciculations and may
    take several days, occasionally weeks, to recover.

    Fatalities have occurred rarely after pyrethroid exposure, usually
    following ingestion (He et al, 1989). No fatalities have been reported
    after bioresmethrin exposure.


    Dermal exposure

         -    Tingling and pruritus with blotchy erythema on the face or
              other exposed areas, exacerbated by sweating or touching.
              Systemic toxicity may ensue following substantial exposure
              (see below).

    Ocular exposure

         -    Lacrimation and transient conjunctivitis may occur.


    Brief exposure:
         -    Respiratory tract irritation with cough, mild dyspnoea,
              sneezing and rhinorrhea.

    Substantial and prolonged exposure:
         -    Systemic toxicity may ensue - see below.


         -    May cause nausea, vomiting and abdominal pain. Systemic
              toxicity may ensue following substantial ingestion (see

    Systemic toxicity

         -    Systemic symptoms may develop after widespread dermal
              exposure, prolonged inhalation or ingestion. Features
              include headache, dizziness, anorexia and hypersalivation.

              Severe poisoning is uncommon. It usually follows substantial
              ingestion and causes impaired consciousness, muscle
              fasciculations, convulsions and, rarely, non-cardiogenic
              pulmonary oedema.

    Chronic exposure

         -    Long-term exposure is no more hazardous than short-term



    1.   Remove soiled clothing and wash contaminated skin with soap and
    2.   Institute symptomatic and supportive measures as required.
    3.   Topical vitamin E (tocopherol acetate) has been shown to reduce
         skin irritation if applied soon after exposure (Flannigan et al,
         1985), but it is not available as a pharmaceutical product in the
    4.   Symptoms usually resolve within 24 hours without specific


    1.   Irrigate with lukewarm water or 0.9 per cent saline for at least
         ten minutes.
    2.   A topical anaesthetic may be required for pain relief or to
         overcome blepharospasm.
    3.   Ensure no particles remain in the conjunctival recesses.
    4.   Use fluorescein stain if corneal damage is suspected.
         If symptoms do not resolve following decontamination or if a
         significant abnormality is detected during examination, seek an
         ophthalmological opinion.


    1.   Remove to fresh air.
    2.   Institute symptomatic and supportive measures as required.


    1.   Do not undertake gastric lavage because solvents are present in
         some formulations and lavage may increase risk of aspiration
    2.   Institute symptomatic and supportive measures as required.
    3.   Atropine may be of value if hypersalivation is troublesome,
         0.6-1.2 mg for an adult, 0.02 mg/kg for a child.
    4.   Mechanical ventilation should be instituted if non-cardiogenic
         pulmonary oedema develops.

    5.   Isolated brief convulsions do not require treatment but
         intravenous diazepam should be given if seizures are prolonged or
         recur frequently. Rarely, it may be necessary to give intravenous
         phenytoin or to paralyze and ventilate the patient.

    Substance name


    Origin of substance

         Bioresmethrin is the [1R,  trans] isomer of resmethrin and has
         greater insecticidal activity than the racemic mixture.

    Synonyms/Proprietary names

         Combat whitefly insecticide
         Penick 1390
         Pyrethroid NRDC 107
         Resbuthrin                              (RTECS, 1997)

    Chemical group

         Type I synthetic pyrethroid

    Reference number

         CAS            28434-01-7               (Pesticide Manual, 1997)
         RTECS          GZ1310500                (RTECS, 1997)
         UN             NIF
         EEC            249-014-0                (Pesticide Manual, 1997)

    Physicochemical properties

    Chemical structure
         IUPAC name: 5-benzyl-3-furylmethyl (1 R)-trans-2,2-dimethyl-3-


                                                 (Pesticide Manual, 1997)

    Molecular weight
         338.4                                   (Pesticide Manual, 1997)

    Physical state at room temperature
         Technical grade bioresmethrin is a viscous liquid which partially
         solidifies on standing.                 (Pesticide Manual, 1997)

         Technical grade bioresmethrin is yellow to brown.
                                                 (Pesticide Manual, 1997)



         Sparingly soluble in water: < 3 x 10 -4 g/L at 25°C
         Ethylene glycol < 10 g/L
         Soluble in ethanol, acetone, chloroform, dichloromethane, ethyl
         acetate, toluene and hexane             (Pesticide Manual, 1997)

    Autoignition temperature

    Major combustion products

    Explosive limits

         Burns with difficulty.                  (HSDB, 1997)

    Boiling point
         Decomposes >180°C                       (Pesticide Manual, 1997)

         1.050 at 20°C                           (Pesticide Manual, 1997)

    Vapour pressure
         1.86 x 10 -2 Pa at 25°C (gas saturation method)
                                                 (Pesticide Manual, 1997)

    Relative vapour density

    Flash point
         Approx. 92°C                            (Pesticide Manual, 1997)



         Bioresmethrin is a potent contact insecticide effective against a
         wide range of household insects, plant pests, grain pests and
         insects found in animal housing (Pesticide Manual, 1997).

    Hazard/risk classification (resmethrin)

    Index no. 613-060-00-3
    Risk phrases
         R22-Harmful if swallowed
    Safety phrases
         S2-Keep out of reach of children        (Pesticide Manual, 1997)


    Pyrethrins were developed as pesticides from extracts of dried and
    powdered flower heads of  Chrysanthemum cinerariaefolium. The active
    principles of these (see Fig. 1) are esters of chrysanthemumic acid
    (R1 = CH3) or pyrethric acid (R1 = CH3O2C) (both cyclopropane
    (three membered ring) carboxylic acids), with one of three
    cyclopentanone alcohols (cinerolone, R2 = CH3; jasomolone, R2 =
    CH2CH3; or pyrethrolone, R2 = CHCH2), giving six possible
    structures. These natural pyrethrins have the disadvantage that they
    are rapidly decomposed by light.

    FIGURE 1

    Once the basic structure of the pyrethrins had been discovered,
    synthetic analogues, pyrethroids, were developed and tested. Initially
    esters were produced using the same cyclopropane carboxylic acids,
    with variations in the alcohol portion of the compounds.

    The first commercial synthetic pyrethroid, allethrin, was produced in
    1949, followed in the 1960s by others including dimethrin,
    tetramethrin and resmethrin. 3-Phenoxybenzyl esters were also found to
    be active as pesticides (e.g. phenothrin, permethrin). Synthetic
    pyrethroids with the basic cyclopropane carboxylic ester structure
    (and no cyano group substitution) are known as type I pyrethroids. In
    animal studies type I pyrethroids have been shown generally to produce
    a typical toxic syndrome (see below).

    The insecticidal activity of synthetic pyrethroids was enhanced
    further by the addition of a cyano group at the benzylic carbon atom
    to give alpha-cyano (type II) pyrethroids. In animal studies type II
    pyrethroids have been shown generally to produce a typical toxic
    syndrome (see below).

    Despite the lack of the cyclopropane ring, similar insecticidal
    activity was found in a group of phenylacetic 3-phenoxybenzyl esters.
    This led to the development of fenvalerate, an
    alpha-cyano-3-phenoxy-benzyl ester, and other related compounds such
    as fluvalinate. These all contain the alpha-cyano group and hence are
    type II pyrethroids.

    Animal studies suggest that the two structural types of pyrethroids
    give rise generally to distinct patterns of systemic toxic effects.
    Type I pyrethroids produce in animals the so-called "T (tremor)
    syndrome", characterized by tremors, prostration and altered "startle"
    reflexes. Type II (alpha-cyano) pyrethroids produce the so-called "CS
    (choreoathetosis/salivation) syndrome" with ataxia, convulsions,
    hyperactivity, choreoathetosis and profuse salivation being observed
    in experimental studies.

    These observations are consistent with some differences in the
    mechanisms of toxicity between type I and type II pyrethroids (see
    below) but the division of reactions by chemical structure is not
    exclusive. Some compounds produce a combination of the two syndromes,
    and different stereoisomeric forms can produce different syndromes
    (Dorman and Beasley, 1991). The classification into "T" and "CS"
    syndromes is not used clinically.

    All pyrethroids have at least four stereoisomers, with different
    orientation of the substituents on the cyclopropane ring (or the
    equivalent part of the phenylacetate). The isomers have different
    biological activities, as discussed below (see Mechanisms of
    toxicity). Different isomers may have separate common names,
    reflecting their commercial importance, for instance bioresmethrin is
    the more active isomer of resmethrin (Aldridge et al, 1978).

    Further details are given in the pyrethroid generic monograph.


    In 1989-1990, world-wide annual production of pyrethroids was at least
    2000 tonnes (IPCS, 1989a; IPCS, 1989b; IPCS, 1989c; IPCS, 1990a; IPCS,
    1990b; IPCS, 1990c; IPCS, 1990d; IPCS, 1990e; IPCS, 1990f) including
    20-30 tonnes of resmethrin and isomers (IPCS, 1989b).

    In spite of their long history of use, there are relatively few
    reports of pyrethroid, and specifically bioresmethrin, toxicity. Less
    than ten deaths have been reported from ingestion or occupational
    (primarily dermal/inhalational) pyrethroid exposure with no deaths
    from bioresmethrin exposure (He et al, 1989; Peter et al, 1996).


    In neuronal cells the generation of an action potential by membrane
    depolarization involves the opening of cell membrane sodium channels
    and a rapid increase in sodium influx. The closure of sodium channels
    begins the process of action potential inactivation. Delayed sodium
    channel closure thus increases cell membrane excitability.

    Pyrethroids modify the gating characteristics of voltage-sensitive
    sodium channels in mammalian and invertebrate neuronal membranes
    (Eells et al, 1992; Narahashi, 1989) to delay their closure. They are
    dissolved in the lipid phase of the membrane (Narahashi, 1996) and
    bind to a receptor site on the alpha sub-unit of the sodium channel
    (Trainer et al, 1997). This binding is to a different site from local
    anaesthetics, batrachotoxin, grayanotoxin, and tetrodotoxin
    (Narahashi, 1996).

    The interaction of pyrethroids with sodium channels is highly
    stereospecific (Soderlund and Bloomquist, 1989), with the 1R and 1S
     cis isomers binding competitively to one site and the 1R and 1S
     trans isomers binding non-competitively to another. The 1S forms do
    not modify channel function but do block the effect of the 1R isomers
    (Ray, 1991).

    The prolonged opening of sodium channels by the neurotoxic isomers of
    pyrethroids produces a protracted sodium influx which is referred to
    as a sodium "tail current" (Miyamoto et al, 1995; Soderlund and
    Bloomquist, 1989; Vijverberg and van den Bercken, 1982). This lowers
    the threshold of sensory nerve fibres for the activation of further
    action potentials, leading to repetitive firing of sensory nerve
    endings (Vijverberg and van den Bercken, 1990) which may progress to
    hyperexcitation of the entire nervous system (Narahashi et al, 1995).
    At high pyrethroid concentrations, the sodium "tail current" may be
    sufficiently great to depolarize the nerve membrane completely,
    generating more open sodium channels (Eells et al, 1992) and
    eventually causing conduction block.

    Only low pyrethroid concentrations are necessary to modify sensory
    neurone function. For example, when tetramethrin was added to a
    preparation of rat cerebellar Purkinje neurons, only about 0.6-1 per
    cent of sodium channels needed to be modified to produce:

    (i)    Repetitive discharges in nerve fibres and nerve terminals;

    (ii)   An increase in discharges from sensory neurons (due to membrane
           depolarization); and

    (iii)  Severe disturbances of synaptic transmission (Narahashi, 1989;
           Narahashi et al, 1995; Song and Narahashi, 1996).

    These effects on sodium channels are common to all pyrethroids
    although specific effects of type I pyrethroids, such as
    bioresmethrin, have been clarified in experimental studies. These show
    that type I compounds:

    (i)    Keep sodium channels open (Narahashi, 1989);

    (ii)   Produce repetitive firing of sensory nerve endings (Soderlund
           and Bloomquist, 1989; Vijverberg and van den Bercken, 1982);

    (iii)  Modify sodium channels in the resting or closed state so that
           they subsequently open more slowly (Dorman and Beasley, 1991);

    (iv)   Show a more pronounced positive temperature-dependent capacity
           for developing repetitive discharges (more likely to occur at
           higher temperatures) and negative temperature dependence for
           nerve-blocking action (more likely to occur at lower
           temperatures) (Clark and Marion, 1989; Dorman and Beasley,
           1991; Narahashi, 1989); and

    (v)    Produce effects on cultured neurons that are easily reversed by
           washing with a pyrethroid-free solution (Song et al, 1996).

    Tetramethrin has also been shown to block voltage-dependent calcium
    channels (Clark and Marion, 1989).

    In human investigations, maximal conduction velocity in sensory nerve
    fibres of the sural nerve showed some increase in subjects exposed to
    pyrethroids, but there were no abnormal neurological signs, and other
    electrophysiological studies were normal in the arms and legs (Le
    Quesne et al, 1980). He et al (1991) assessed nerve excitability using
    an electromyograph and pairs of stimuli at variable intervals. They
    showed a prolongation of the "supernormal period" in the median nerve
    in individuals who had been exposed to pyrethroids occupationally for
    three days. The "supernormal period" was even more prolonged two days
    after cessation of exposure. (Note: the "supernormal period" is the
    period for which the action potential induced by a second stimulus is
    greater than the action potential produced by an initial stimulus).

    Pyrethroids are some 2250 times more toxic to insects than mammals.
    This can be explained in terms of differences in their potency as
    neuronal toxins and differences in rates of detoxification between
    invertebrates and vertebrates (Narahashi, 1996; Narahashi et al, 1995;
    Song and Narahashi, 1996).

    The sensitivity of invertebrate neuronal sodium channels to
    pyrethroids is ten times greater than in mammals (Song and Narahashi,
    1996). Furthermore, invertebrates typically have body temperatures
    some 10°C lower than mammals and  in vitro studies show tetramethrin
    to be more potent at evoking repetitive neuronal discharges at lower
    temperatures (Song and Narahashi, 1996). In these experiments it was
    noted that the recovery of sodium channels from tetramethrin
    intoxication after washing was some five times faster in mammals than

    invertebrates. In addition pyrethroid hepatic metabolism
    (detoxification) is faster in mammals. Finally small insect size
    increases the likelihood of end-organ (neuronal) toxicity prior to
    detoxification (Song and Narahashi, 1996).


    In addition to the important differences between invertebrates and
    vertebrates outlined above, the low toxicity of pyrethroid
    insecticides in mammals is due to poor dermal absorption (the main
    route of exposure) and metabolism to non-toxic metabolites (Bradbury
    and Coats, 1989).



    Based on excretion studies involving other pyrethroids (Nassif et al,
    1980; Chester et al, 1987; Eadsforth et al, 1988; van der Rhee et al,
    1989; IPCS, 1990f; Woollen et al, 1991; Woollen et al, 1992), dermal
    absorption of bioresmethrin is likely to be low (less than 1.5 per


    Between 19 and 57 per cent of orally administered cypermethrin (a type
    II pyrethroid) was absorbed in human studies (Woollen et al, 1991;
    Woollen et al, 1992). There are no human data specific to


    Pyrethroids are hydrolyzed rapidly in the liver to their inactive acid
    and alcohol components (Hutson, 1979; Ray, 1991), probably by
    microsomal carboxylesterase (Hutson, 1979). Further degradation and
    hydroxylation of the alcohol at the 4' position then occurs, and
    oxidation produces a wide range of metabolites (Hutson, 1979; Leahey,

    There is some stereospecificity in metabolism, with  trans-isomers
    being hydrolyzed more rapidly than the  cis-isomers, for which
    oxidation is the more important metabolic pathway (Soderlund and
    Casida, 1977).

    The pattern of metabolites varies between oral and dermal dosing in
    humans (Wilkes et al, 1993). For example, following dermal dosing with
    cypermethrin (a type II pyethroid) the ratio of  trans/cis 
    cyclopropane acids excreted was approximately 1:1, compared to 2:1
    after oral administration. Such measurements might be useful in
    determining the route of exposure (Woollen, 1993; Woollen et al, 1991;
    Woollen et al, 1992).

    Animal studies have shown that pyrethroid hydrolysis is inhibited by
    dialkylphosphorylating agents such as organophosphorus insecticides
    (Abou-Donia et al, 1996; He et al, 1990; Hutson, 1979), and urinary
    excretion of unchanged pyrethroid was higher in sprayers using a
    methamidophos/ deltamethrin or methamidophos/fenvalerate mixture than
    from those using the pyrethroid alone (Zhang et al, 1991).

    Experiments with chickens (Abou-Donia et al, 1996) showed that
    pyrethroid (permethrin) toxicity was also enhanced by pyridostigmine
    bromide and by the insect repellent N,N-diethyl-m-toluamide (DEET).
    The authors hypothesized that competition for hepatic and plasma
    esterases by these compounds led to decreased pyrethroid breakdown and
    increased transport of the pyrethroid to neural tissues.


    Bioresmethrin is excreted mainly as metabolites in urine but a
    proportion is excreted unchanged in faeces. An overview of human
    pyrethroid elimination data is included in the generic pyrethroid
    monograph though there are no human data for bioresmethrin.


    Occupationally, the main route of pyrethroid absorption is through the
    skin; inhalation is much less important (Adamis et al, 1985; Chen et
    al, 1991; Zhang et al, 1991). Inhalation is more likely when
    pyrethroids are used in confined spaces (Llewellyn et al, 1996). The
    use of protective clothing can reduce dermal exposure (Chester et al,
    1987). The physical formulation also affects exposure, with inhalation
    being more important for dust and powder formulations, and dermal
    exposure more important for liquids (Llewellyn et al, 1996).

    Dermal exposure

    This is the most common route of pyrethroid exposure. Adverse effects
    manifest primarily as peripheral neurotoxicity with reversible
    hyperactivity of sensory nerve fibres (paraesthesiae), though erythema
    and pruritus are also described (see below).

    Peripheral neurotoxicity

    Paraesthesiae have been reported frequently, particularly after the
    inappropriate handling of pyrethroids, though there are no cases
    specific to bioresmethrin. Paraesthesiae occur most commonly on the
    face (He et al, 1991). It seems probable that paraesthesiae are
    related to the repetitive firing of sensory nerve endings in
    contaminated skin (Aldridge, 1990) and not to inflammation as there is
    little effect on neurogenic vasodilatation (Flannigan and Tucker,
    1985b). The symptoms are exacerbated by sensory stimulation (heat,
    sun, scratching) (Aldridge, 1990), sweating or application of water
    and may prevent sleep (Tucker and Flannigan, 1983).

    Paraesthesiae generally start 30 minutes to two hours after exposure
    and peak after about six hours. Recovery is usually complete within 24
    hours (Aldridge, 1990; He et al, 1989; Knox and Tucker, 1982; Knox et
    al, 1984; Tucker and Flannigan, 1983).

    Dermal toxicity

    When used at recommended doses in the treatment of scabies and lice,
    pyrethroids only rarely produce adverse effects. Pruritus is the
    side-effect reported most frequently (Brandenburg et al, 1986;
    DiNapoli et al, 1988), although this may also be caused by the skin
    infestation being treated.

    Skin irritation during occupational pyrethroid exposure may occur in
    up to ten per cent of workers (Kolmodin-Hedman et al, 1982) and may be
    influenced by the ratio of stereoisomers used in the pyrethroid
    formulation. In addition to pruritus, erythema, burning and blisters
    have been reported (Brandenburg et al, 1986; Kalter et al, 1987; IPCS,
    1990b; Kolmodin-Hedman et al, 1995).

    There are no reports of dermal toxicity specifically following
    bioresmethrin exposure.

    Ocular exposure

    Symptoms of mild eye irritation have been reported following
    occupational pyrethroid exposure but there are no reports specific to
    bioresmethrin (Kolmodin-Hedman et al, 1982; IPCS, 1990d; Lessenger,


    Inhalational pyrethroid exposure typically is occupational and
    produces symptoms and signs of pulmonary tract irritation. The
    frequency and severity of symptoms may vary with the ratio of
    different stereoisomers in a formulation, being more prevalent with a
    higher proportion of the  trans isomer. Systemic effects may occur
    following more substantial exposure (He et al, 1989) and are described
    below. There are no reports specific to bioresmethrin exposure.


    Pyrethroid ingestion typically gives rise to nausea, vomiting and
    abdominal pain within minutes. In one series (He et al, 1989)
    involving some 344 cases, vomiting was a prominent feature in 56.8 per
    cent though none were known to involve bioresmethrin.

    Substantial pyrethroid ingestion may give rise to neurological
    features and other systemic effects as discussed below.

    Systemic effects

    Systemic effects generally have occurred after inappropriate
    occupational handling of pyrethroids. This may involve using too
    concentrated solutions, prolonged exposure, spraying against the wind
    or using unprotected hands or mouth to unblock congested sprayers (He
    et al, 1989). Most reported cases have involved dermal, inhalational
    and sometimes also oral exposure to fenveralate, deltamethrin or
    cypermethrin with systemic features occurring between four and 48
    hours after spraying (He et al, 1989). Intentional ingestion may also
    produce systemic effects (He et al, 1989; Peter et al, 1996). Most
    patients recover over two to four days with only seven fatalities
    among 573 cases in one review (He et al, 1989). Four of the seven
    fatalities developed convulsions, one patient died from
    non-cardiogenic pulmonary oedema, one from "atropine intoxication" and
    one death followed exposure to a pyrethroid/organophosphorus pesticide

    A further death has been reported recently in a patient who became
    comatose within ten hours of 30 mL deltamethrin ingestion and died
    from aspiration pneumonia complicated by renal failure (Peter et al,

    There are no reports of systemic toxicity specific to bioresmethrin

    Gastrointestinal toxicity

    As discussed above gastrointestinal irritation is common following
    pyrethroid ingestion. Vomiting was a prominent symptom also in 16 per
    cent of  occupational cases (He et al, 1989) in whom ingestion was
    not suspected, but where exposure involved deltamethrin, cypermethrin
    or fenvalerate. In this review, which included occupational exposures,
    anorexia occurred in 45 per cent of 573 cases of acute pyrethroid
    poisoning (He et al, 1989).


    He et al (1989) described dizziness in 60.6 per cent, headache in 44.5
    per cent, fatigue in 26 per cent, increased salivation in 20 per cent
    and blurred vision in seven per cent of 573 cases of acute pyrethroid
    poisoning (229 occupational and 344 accidental exposures).

    Limb muscle fasciculations, coma and convulsions may complicate severe
    acute pyrethroid poisoning, and have occurred as soon as 20 minutes
    after ingestion (He et al, 1989). "Convulsions" was the stated cause
    of death in four of seven fatalities among 573 cases of acute
    pyrethroid (not bioresmethrin) poisoning (He et al, 1989) but further
    details were not given.

    An electromyelogram (EMG) in one case of acute pyrethroid (not
    specified) poisoning showed repetitive muscle discharges without
    denervation potentials (He et al, 1989).

    There is animal evidence that the neurotoxicity of permethrin is
    increased by pyridostigmine and by DEET (Abou-Donia et al, 1996;
    McCain et al, 1997).

    Cardiovascular toxicity

    Palpitation was reported in 13.1 per cent of 573 cases of acute
    pyrethroid poisoning involving oral, inhalational and dermal exposure
    to deltamethrin, fenvalerate or cypermethrin (He et al, 1989). An
    electrocardiogram (ECG) showed ST and T wave changes in eight of 71
    patients. Other ECG abnormalities included sinus tachycardia,
    ventricular ectopics and (rarely) sinus bradycardia (He et al, 1989).
    All ECG changes resolved in 2-14 days.

    Pulmonary toxicity

    Chest tightness has been described following accidental or deliberate
    pyrethroid ingestion (He et al, 1989).

    Non-cardiogenic pulmonary oedema has been reported rarely following
    substantial pyrethroid ingestion, usually in association with severe
    neurological complications, and may contribute to a fatal outcome (He
    et al, 1989).

    Musculoskeletal toxicity

    A case of acute polyarthralgia after skin exposure to flumethrin (a
    type II pyrethroid) has been reported recently (Box and Lee, 1996).


    Among 235 cases of occupational or accidental acute pyrethroid
    poisoning in whom a full blood count was performed, 15 per cent showed
    a leucocytosis (He et al, 1989); this was probably a non-specific


    Urinalysis among 124 patients with acute pyrethroid poisoning
    (involving oral, dermal and inhalational exposure to deltamethrin,
    fenvalerate or cypermethrin) showed three patients with haematuria (He
    et al, 1989).


    Dermal exposure

    Few long-term adverse effects from pyrethroids have been reported
    (IPCS, 1990d; Chen et al, 1991, He, 1994). There is no confirmed
    evidence that repeated exposure to pyrethroids leads to permanent
    damage to sensory nerve endings (Vijverberg and van den Bercken,

    In a study of 199 workers exposed for several months to deltamethin,
    fenvalerate and cypermethrin (all type II pyrethroids) in a packaging
    plant, the symptoms described were identical to those following acute
    pyrethroid exposure and did not last more than 24 hours once subjects
    were away from the work environment (He et al, 1988). This suggests
    there are no true  chronic effects from repeated pyrethroid exposure.


    Sixty-four (32 per cent) of the 199 workers described above complained
    of sneezing and increased nasal secretions but these symptoms were
    only present at work, again suggesting no difference in effect between
    chronic or acute pyrethroid exposure. Systemic symptoms of dizziness,
    fatigue and nausea were mild and reported by only 14, nine and ten per
    cent of workers respectively.


    Dermal exposure


    Clothes contaminated with bioresmethrin should be removed, and
    contaminated skin washed with soap and water (He, 1994).

    Specific measures

    Topical alpha tocopherol (vitamin E) to treat paraesthesiae

    As paraesthesiae usually resolve in 12-24 hours, specific treatment is
    not generally administered or required. However, the topical
    application of  dl-alpha tocopherol acetate (vitamin E) has been
    shown to reduce the severity of skin reactions to other pyrethroids
    including fenvalerate (IPCS, 1990c; Tucker et al, 1984; Tucker et al,
    1983), flucythrinate, permethrin and cypermethrin (Flannigan and
    Tucker, 1985a). The reaction to cypermethrin was completely inhibited
    by vitamin E (Flannigan et al, 1985). Vitamin E appears to be useful
    both prophylactically and therapeutically (Flannigan and Tucker,
    1985a). In a controlled human volunteer study, a commercial vitamin E
    oil preparation produced 98 per cent inhibition of the cutaneous
    symptoms from fenvalerate when applied immediately (Flannigan et al,
    1985). At four hours the inhibition was only 50 per cent (Advisory
    Committee on Pesticides, 1992). The mechanism of the effect of topical
    vitamin E has not been clarified, although some  in vitro studies
    suggest vitamin E may block the pyrethroid-induced sodium "tail
    current" in neuronal membranes (Song and Narahashi, 1995).

    Vitamin E is not included in the British National Formulary but is
    available from health food or alternative medicine sources.

    Other agents to treat paraesthesiae

    Various other topical therapies have been tested for treatment of
    pyrethroid-induced paraesthesiae: in clinical trials mineral oil, corn
    oil and "A&D ointment" (Tucker et al, 1984; Tucker et al, 1983) were
    almost as effective as Vitamin E cream (but the oils may lead to
    defatting of skin). Butylated hydroxyanisole and an industrial barrier
    cream (Tucker et al, 1984) and topical indomethacin (Flannigan and
    Tucker, 1984), were of little therapeutic benefit and in two studies
    zinc oxide paste exacerbated paraesthesiae (Tucker et al, 1984; Tucker
    et al, 1983).

    Ocular exposure

    Irrigate the affected eye with lukewarm water or 0.9 per cent saline
    for at least ten minutes. A topical anaesthetic may be required for
    pain relief or to overcome blepharospasm. Ensure no particles remain
    in the conjunctival recesses. Use fluorescein if corneal damage is
    suspected. If symptoms do not resolve following decontamination or if
    a significant abnormality is detected during examination, seek an
    ophthalmological opinion.


    Removal from exposure is the priority. Mild symptoms of rhinitis
    respond to oral antihistamines. Other symptomatic and supportive
    measures should be dictated by the patient's condition.


    Gut decontamination

    Gastric lavage should be avoided since solvents present in many
    bioresmethrin formulations may increase the risk of aspiration

    Systemic toxicity

    Most patients exposed to bioresmethrin require only simple supportive
    care. Systemic toxicity is rare but in such patients the presence of
    excess salivation, muscle fasciculations and pulmonary oedema may
    present diagnostic difficulty since similar features are typical also
    of severe organophosphorus pesticide poisoning. Measurement of the red
    cell cholinesterase activity (which is reduced in acute
    organophosphorus poisoning but not in pyrethroid intoxication) allows
    clarification but may not be available rapidly.

    Isolated brief convulsions do not require treatment but intravenous
    diazepam 5-10 mg should be given if seizures are prolonged. Rarely it
    may be necessary to give intravenous phenytoin, or to paralyze and
    ventilate the patient. Diazepam is useful also in the treatment of
    muscle fasciculations. The role of atropine is discussed below.

    Several experimental studies have investigated the role of
    pharmaceuticals in the management of the neurological complications of
    severe pyrethroid poisoning. However, these should be interpreted with
    caution, not only because they usually have involved high-dose
    parenteral pyrethroid administration, but also because there is
    considerable interspecies variation with regard to therapeutic
    efficacy (Casida et al, 1983; Vijverberg and van den Bercken, 1990).

    Atropine for hypersalivation and pulmonary oedema

    In experimental studies atropine sulphate (25 mg/kg subcutaneously)
    reduced hypersalivation produced by oral fenvalerate or cypermethrin
    (each at a dose exceeding the LD50), but did not increase survival
    (Hiromori et al, 1986).

    Intravenous atropine (0.6-1.2 mg in an adult) may be useful to control
    excess salivation but care should be taken to avoid excess
    administration. In a review of pyrethroid poisoning cases reported
    from China (He et al, 1989), 189 of 573 patients were treated with
    atropine which led to an improvement in salivation and pulmonary
    oedema in a few severe cases, but eight patients developed atropine
    intoxication following intravenous administration of 12-75 mg. One
    patient, probably misdiagnosed as having acute organophosphorus
    insecticide poisoning, died of atropine intoxication after a total
    dose of 510 mg, and one patient acutely intoxicated with a
    fenvalerate/dimethoate mixture could not be revived despite a total
    atropine dose of 170 mg.

    Atropine and ethylcarbamate

    In a French study a combination of intravenous atropine 3 mg/kg and
    ethylcarbamate 1000 mg/kg effectively protected rodents against the
    lethal effects of intravenous deltamethrin, increasing the LD50 by a
    factor of 3.48 (Leclercq et al, 1986).

    Diazepam and phenobarbital for convulsions

    In mice (n=10) pre-treatment with intraperitoneal diazepam (1 mg/kg),
    but not phenobarbital (10-30 mg/kg), significantly increased the time
    to onset of convulsions caused by the intracerebroventricular
    administration of deltamethrin (p< 0.005) and fenvalerate (p<0.05)
    (Gammon et al, 1982). Under the same conditions diazepam was not
    effective in preventing permethrin- or allethrin-induced seizures.

    Propranolol and procainamide for tremor

    Pre-treatment with intravenous propranolol or procainamide (each 15
    µmol/kg) reduced the severity of tremor or writhing induced in rats by
    the intravenous administration of deltamethrin (10 µmol/kg) (Bradbury
    et al, 1983).

    Ivermectin and pentobarbital for choreoathetosis

    In rodents administered 2 mg/kg intravenous deltamethrin,
    pre-treatment with 4 mg/kg intravenous ivermectin reduced
    choreoathetosis from 3.9 to 3.2 (as graded on a scale of 1-4) 
    (p = 0.023), and reduced salivation by 72 per cent. Pentobarbital 
    (15 mg/kg i.p.) reduced choreoathetosis produced by 1.5 mg/kg
    intravenous deltamethrin from 3.0 to 1.3 (p = 0.004). An equi-sedative
    dose of phenobarbital produced a non-significant fall to 2.4 
    (p = 0.11) (Forshaw and Ray, 1997).

    Mephenesin and methocarbamol

    The skeletal muscle relaxant mephenesin 22 µmol/kg prevented all motor
    symptoms induced in rats by the intravenous administration of
    deltamethrin (10 µmol/kg) (n=4-20 in different treatment groups)
    (Bradbury et al, 1983).

    Mephenesin has a short half-life in vivo, but intraperitoneal
    methocarbamol (a mephenesin derivative) (400 mg/kg intraperitoneally
    followed by 200 mg/kg whenever tremor was observed) significantly
    (p<0.01) reduced mortality in rats administered more than the oral
    LD50 of fenvalerate, fenpropathrin, cypermethrin or permethrin (n=10
    in each treatment group) (Hiromori et al, 1986).

    There are insufficient data to advocate a clinical role for
    methocarbamol in systemic pyrethroid toxicity.

    Sodium-channel blockers (local anaesthetics)

     In vitro studies suggest local anaesthetics may be useful as
    antagonists of the effect of deltamethrin on sodium channels
    (Oortgiesen et al, 1990). The relevance to human poisoning is not


    Avoiding dermal and inhalational exposure via adequate self-protection
    and sensible use is the most important requirement to reduce adverse
    effects from occupational use of bioresmethrin.


    Maximum exposure limit

    International Standards Organization (ISO) limits for natural
    pyrethrins: long-term exposure limit (8 hour TWA reference period) 5
    mg/m3; short-term exposure limit (15 min reference period) 10
    mg/m3 (Health and Safety Executive, 1995).


    Endocrine toxicity

     In vitro studies show that several pyrethroids interact
    competitively with human skin fibroblast androgen receptors and with
    sex hormone binding globulin (with the relative potency being
    bioallethrin > fenvalerate > fenothrin > fluvalinate > permethrin
    > resmethrin) (Eil and Nisula, 1990). A possible anti-androgenic
    effect of pyrethroids in humans was suggested following an outbreak of
    gynaecomastia in refugees exposed to fenothrin, but there was
    insufficient evidence to confirm this (Eil and Nisula, 1990).

    Animal studies evaluating other endocrine effects of pyrethroids have
    produced conflicting results (Akhtar et al, 1996; Kaul et al, 1996).


    In oral dosing studies in rodents, several pyrethroids suppressed the
    cellular immune response (Blaylock et al, 1995; Tulinská et al, 1995)
    or produced thymus atrophy (Madsen et al, 1996).

    The significance of these immunological studies to man is not known.


    There is no evidence that bioresmethrin is carcinogenic (IPCS, 1989b).


    There is no evidence that bioresmethrin is teratogenic, embryotoxic or
    fetotoxic (IPCS, 1989b).


    Data regarding the potential genotoxicity of pyrethroids provide
    conflicting results (Puig et al, 1989; Barrueco et al, 1992; Herrera
    et al, 1992; Dolara et al, 1992; Barrueco et al, 1994; Surrallés et
    al, 1995), though toxicity reviews of  in vitro and  in vivo data
    for most compounds, including resmethrin (IPCS, 1989b), conclude there
    is insufficient evidence for them to be considered genotoxic or

    Fish toxicity

    Bioresmethrin is toxic to fish. It is more toxic at cooler
    temperatures, and thus more toxic to cold than warm water fish, but
    the toxicity of pyrethroids is little affected by pH or water hardness
    (Mauck et al, 1976).

    LC50 (96 hr) for harlequin fish is 0.014 mg/L bioresmethrin, for
    guppies is 0.5-1.0 mg/L bioresmethrin, for rainbow trout is 0.00062
    mg/L bioresmethrin, and for bluegill sunfish is 0.0024 mg/L
    bioresmethrin (Pesticide Manual, 1997).

    LC50 (48 hr) for harlequins is 0.018 mg/L bioresmethrin, and for
    guppies is 0.5-1.0 mg/L bioresmethrin (Pesticide Manual, 1997).

    EC Directive on Drinking Water Quality 80/778/EEC

    Maximum admissible concentration (any pesticide) 0.1 µg/L (EC
    Directive, 1980).


    SA Cage MSc M Inst Inf Sci
    SM Bradberry BSc MB MRCP
    S Meacham BSc

    National Poisons Information Service (Birmingham Centre),
    West Midlands Poisons Unit,
    City Hospital NHS Trust,
    Dudley Road,
    B18 7QH

    This monograph was produced by the staff of the Birmingham Centre of
    the National Poisons Information Service in the United Kingdom. The
    work was commissioned and funded by the UK Departments of Health, and
    was designed as a source of detailed information for use by poisons
    information centres.

    Date of last revision


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