IPCS INCHEM Home
    UKPID MONOGRAPH




    PERMETHRIN




    SA Cage MSc M Inst Inf Sci
    SM Bradberry BSc MB MRCP
    S Meacham BSc
    JA Vale MD FRCP FRCPE FRCPG FFOM

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


    PERMETHRIN

    Toxbase summary

    Type of product

    Insecticide

    Toxicity

    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 known fatalities have been
    reported after permethrin exposure.

    Features

    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.

    Inhalation

    Brief exposure:

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

    Substantial and prolonged exposure:

         -    Systemic toxicity may ensue - see below.

    Ingestion

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

    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
              exposure.

    Management

    Dermal

    1.   Remove soiled clothing and wash contaminated skin with soap and
         water.
    2.   Institute symptomatic and supportive measures as required.
         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
         UK.
    3.   Symptoms usually resolve within 24 hours without specific
         treatment.

    Ocular

    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.
    5.   If symptoms do not resolve following decontamination or if a
         significant abnormality is detected during examination, seek an
         ophthalmological opinion.

    Inhalation

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

    Ingestion

    1.   Do not undertake gastric lavage because solvents are present in
         some formulations and lavage may increase risk of aspiration
         pneumonia.
    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.

    References

    Box SA, Lee MR.
    A systemic reaction following exposure to a pyrethroid insecticide.
    Hum Exp Toxicol 1996; 15: 389-90.

    Flannigan SA, Tucker SB, Key MM, Ross CE, Fairchild EJ, Grimes BA,
    Harrist RB.
    Synthetic pyrethroid insecticides: a dermatological evaluation.
    Br J Ind Med 1985; 42: 363-72.

    He F, Wang S, Liu L, Chen S, Zhang Z, Sun J.
    Clinical manifestations and diagnosis of acute pyrethroid poisoning.
    Arch Toxicol 1989; 63: 54-8.

    Lessenger JE.
    Five office workers inadvertently exposed to cypermethrin.
    J Toxicol Environ Health 1992; 35: 261-7.

    O'Malley M.
    Clinical evaluation of pesticide exposure and poisonings.
    Lancet 1997; 349: 1161-6.

    Substance name

         Permethrin

    Origin of substance

         Permethrin was first synthesized as one of the new photostable
         pyrethroids in 1973, and was first marketed in 1977. It contains
         four stereoisomers (IPCS, 1990b).

    Synonyms/Proprietary names

         Ambush
         Anomethrin N
         Chinetrin
         Coopex WP
         Corsair
         Darmycel Agarifume Smoke Generator
         Dragnet
         Ecsmin

         Ectiban
         Efmethrin
         Exmin
         Fumite Permethrin Smoke
         Indothrin
         Ipitox
         Kafil
         Kestrel
         Outflank
         Perigen
         Permasect 10 EC
         Permasect 25 EC
         Permit
         Picket
         Pounce
         Pramex
         Sanathrin
         Stomoxin
         Tubair Permethrin             (RTECS, 1997; Pesticide Manual,
                                       1997; Pesticides 1997, 1997; The UK
                                       Pesticide Guide, 1997)

    Chemical group

         Type I synthetic pyrethroid

    Reference numbers

         CAS            52645-53-1               (Pesticide Manual, 1997)
         RTECS          GZ1255000                (RTECS, 1997)
         UN             NIF
         HAZCHEM CODE   NIF
         EEC            258-067-9

    Physicochemical properties

    Chemical structure
         IUPAC name: 3-phenoxybenzyl (1 RS)-cis,trans-3-(2,2-
         dichlorovinyl)-2,2-dimethylcyclopropanecarboxylate

    CHEMICAL STRUCTURE 1

    C21H20Cl2O3
                                                 (Pesticide Manual, 1997)

    Molecular weight
         391.3                                   (Pesticide Manual, 1997)

    Physical state at room temperature
         Technical grade is a liquid, which sometimes tends to crystallize
         partly at room temperature.             (Pesticide Manual, 1997)

    Colour
         The technical grade is yellow brown to brown.
                                                 (Pesticide Manual, 1997)

    Odour
         NIF

    Viscosity
         NIF

    pH
         NIF

    Solubility
         Low solubility in water: approx. 2 x 10-4 g/L at 30°C
         Xylene, hexane > 900 g/L
         Methanol 204 g/L                        (Pesticide Manual, 1997)

    Autoignition temperature
         NIF

    Major products of combustion
         When heated to decomposition toxic fumes of hydrogen chloride are
         emitted.                                (HSDB, 1997)

    Explosive limits
         NIF

    Flammability
         Burns with difficulty.                  (HSDB, 1997)

    Boiling point
         200°C at 0.1 mm Hg (13.3 Pa)
         >290°C at 760 mm Hg (1 x 105 Pa)
                                                 (Pesticide Manual, 1997)

    Density
         1.19-1.27 at 20°C                       (Pesticide Manual, 1997)

    Vapour pressure
         7 x 10-5 Pa at 20 °C
          cis- 2.5 x 10-6 Pa at 20°C
          trans- 1.5 x 10-6 Pa at 20°C
                                                 (Pesticide Manual, 1997)

    Relative vapour density
         NIF

    Flash point
         'Perigen' > 100°C                       (Pesticide Manual, 1997)

    Reactivity
         NIF

    Uses

         Permethrin is a contact insecticide which is effective against a
         broad range of pests (Pesticide Manual, 1997). Topical permethrin
         is recommended for the treatment of scabies and head lice (BNF,
         1997).

    Hazard/risk classification

    EC Risk: Xn (R22) sensitizing, harmful if swallowed.
                                                 (Pesticide Manual, 1997)

    INTRODUCTION

    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 this 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 tremor, 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 (Aldridge et al, 1978).

    Further details are given in the pyrethroid generic monograph.

    EPIDEMIOLOGY

    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
    approximately 600 tonnes of permethrin (IPCS, 1990b).

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

    MECHANISMS OF TOXICITY

    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 permethrin,
    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).

    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).

    TOXICOKINETICS

    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).

    Absorption

    Dermal

    Based on excretion studies involving permethrin and 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 permethrin is likely to be low (less than
    1.5 per cent).

    Some 0.5 per cent of the total dose of permethrin cream (5 per cent)
    applied to the skin of patients with scabies was excreted (as
    metabolites) in the first 48 hours after application, implying limited
    absorption (van der Rhee et al, 1989). When permethrin was applied in
    a powder formulation to patients with body lice, less than one per
    cent of a 125 mg dose and some 1.5 per cent of a 250 mg dose was
    retrieved as metabolites in urine (Nassif et al, 1980).

    When protective clothing was used the concentrations of permethrin
    metabolites in urine at the end of a working day were at the limit of
    detection (Desi et al, 1986).

    Oral

    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 permethrin.

    Metabolism

    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,
    1985).

    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). 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.

    Elimination

    Permethrin 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.

    When permethrin was used in a five per cent cream to treat scabies,
    about 0.5 per cent of the total dose was excreted as metabolites in 48
    hours, but metabolites were still detectable in urine collected on day
    seven in three of ten patients, and on day 14 in one patient (van der
    Rhee et al, 1989). No detectable metabolites were found 30 or 60 days
    after patients had been treated with a powder formulation of
    permethrin for body lice (Nassif et al, 1980).

    CLINICAL FEATURES: ACUTE EXPOSURE

    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 following permethrin
    exposure (Le Quesne et al, 1980; Kolmodin-Hedman et al, 1982;
    Flannigan and Tucker, 1985a; IPCS, 1990b), particularly after
    inappropriate handling. 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).

    In two studies, paraesthesiae were reportedly more severe after
    deltamethrin and flucythrinate exposure, less after cypermethrin and
    fenvalerate, and least after permethrin exposure (Flannigan and
    Tucker, 1985a; Aldridge, 1990). Ten of 52 workers handling fenvalerate
    developed paraesthesiae compared to none handling permethrin
    (Kolmodin-Hedman et al, 1982).

    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,
    permethrin only rarely produces 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).

    In one clinical trial of permethrin scabies treatment, none of the ten
    patients treated with 21-32 g five per cent permethrin cream reported
    any side effects (van der Rhee et al, 1989). In a second trial, 1/28
    patients treated with one per cent permethrin developed mild
    testicular erythema and irritation 12 hours after application (Kalter
    et al, 1987). In trials of head lice treatments, only three of ten
    patients treated with 15-40 mL one per cent permethrin solution
    reported mild erythema (IPCS, 1990b). In a further study (Brandenburg
    et al, 1986) involving 287 patients given a single application of one
    per cent permethrin, pruritus was the side-effect reported most
    frequently occurring in 5.6 per cent of patients. A burning sensation
    occurred in the affected area in 3.1 per cent of cases, erythema was
    present in 1.4 per cent, and tingling occurred in 1.0 per cent of
    patients (Brandenburg et al, 1986). Ten volunteers who wore
    permethrin-treated clothes, giving an average exposure of 3.8 mg/day,
    reported no irritation (IPCS, 1990b).

    In a double-blind study of occupational exposure, skin symptoms could
    not be related to the degree of dermal permethrin exposure
    (Kolmodin-Hedman et al, 1995). In another study, cutaneous symptoms
    were more severe from permethrin formulations containing a higher
    proportion of the  trans isomer (Kolmodin-Hedman et al, 1982). The
    most common symptoms were: itching (two per cent of 45 workers exposed
    to permethrin with a  trans/cis ratio 60/40, none of 42 workers
    exposed to permethrin with a  trans/cis ratio 75/25); burning (none
    and 12 per cent respectively); blisters (none and ten per cent
    respectively) and a "dry feeling in the face" (12 per cent after 75/25
     trans/cis permethrin exposure only).

    Allergic reactions to pyrethroids are uncommon. Lisi (1992) assessed
    230 volunteers for irritant or delayed contact sensitivity reactions
    to a range of pyrethroids. Two (non-atopic) patients had irritant
    reactions to five per cent resmethrin and a further two had positive
    patch tests to one per cent fenvalerate. There were no positive
    reactions to allethrin, deltamethrin, fenothrin or permethrin.

    In a double blind study of occupational permethrin exposure, two of 18
    workers who developed mucosal blisters and one who had eczematous
    changes on the leg, gave negative skin tests to permethrin
    (Kolmodin-Hedman et al, 1995).

    Ocular exposure

    Symptoms of mild eye irritation have been reported following
    occupational pyrethroid exposure (Kolmodin-Hedman et al, 1982; IPCS,
    1990d; Lessenger, 1992).

    Eye irritation was reported after permethrin was splashed in the eye
    (Kolmodin-Hedman et al, 1982).

    Inhalation

    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.

    Thirteen per cent of 42 workers handling permethrin  (trans/cis 
    75/25)-treated seedlings but only two per cent of 45 workers handling
    permethrin  (trans/cis 60/40)-treated seedlings complained of
    increased nasal secretions during a six hour exposure (Kolmodin-Hedman
    et al, 1982).

    Cough and dyspnoea were reported in eight and two per cent of 42
    workers exposed to permethrin  trans/cis 75/25, but none of 45
    workers exposed to permethrin  trans/cis 60/40 (Kolmodin-Hedman et
    al, 1982).

    Ingestion

    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. In one case, permethrin/pyrethrins accidentally sprayed directly
    into the mouth resulted in a burning sensation which commenced several
    hours after exposure, and only gradually improved over five months,
    with persistent disordered taste sensation (Grant, 1993).

    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
    combination.

    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,
    1996).

    There are no reports of severe systemic toxicity following permethrin
    exposure.

    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).

    Neurotoxicity

    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 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
    (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).

    Haemotoxicity

    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
    response.

    Nephrotoxicity

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

    CLINICAL FEATURES: CHRONIC EXPOSURE

    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,
    1990).

    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.

    Inhalation

    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.

    MANAGEMENT

    Dermal exposure

    Decontamination

    Clothes contaminated with permethrin 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 permethrin
    (Flannigan and Tucker, 1985a) and other pyrethroids including
    fenvalerate (IPCS, 1990c; Tucker et al, 1984; Tucker et al, 1983),
    flucythrinate 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.

    Inhalation

    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.

    Ingestion

    Gut decontamination

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

    Systemic toxicity

    Most patients exposed to permethrin 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
    known.

    MEDICAL SURVEILLANCE

    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 permethrin.

    OCCUPATIONAL DATA

    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).

    OTHER TOXICOLOGICAL DATA

    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).

    Immunotoxicity

    In oral dosing studies in rodents, permethrin at a concentration of
    one per cent LD50 for ten days suppressed the cellular immune
    response (Blaylock et al, 1995). The significance of this study to man
    is not known.

    Carcinogenicity

    The International Agency for Research on Cancer has concluded that
    permethrin is unclassifiable as to its carcinogenicity to humans
    (IARC, 1991).

    Reprotoxicity

    There is no evidence that permethrin is teratogenic, embryotoxic or
    fetotoxic (IPCS, 1990b; Reprotox, 1997).

    No teratogenic effects were observed among the offspring of mice fed
    15-150 mg/kg/day of permethrin during pregnancy (IPCS, 1990b).
    Similarly, the frequency of malformations was not increased among the
    offspring of rats or rabbits fed permethrin during pregnancy in doses
    of 4-225 mg/kg/day or 16-1800 mg/kg/day (IPCS, 1990b). There are no
    human reprotoxicity data for permethrin.

    Genotoxicity

    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 permethrin (IPCS, 1990b), conclude that
    there is insufficient evidence for them to be considered genotoxic or
    mutagenic.

    Permethrin showed no genotoxicity in  Salmonella typhimurium TA98,
    TA100, TA1535, TA1537, TA1538 with or without metabolic activation, or
    in an  Escherichia coli reverse mutation test with or without
    metabolic activation. Permethrin was non-mutagenic  in vitro in
    Chinese hamster V79 cells with and without metabolic activation (DOSE,
    1997).

    The IC50 for  in vitro human lymphocytes cell growth inhibition was
    54.7 mg/L permethrin and the IC50 for protein synthesis inhibition
    was 48.9 mg/L permethrin (DOSE, 1997).

    The IC50 for  in vitro mouse L1210 lymphoblastoid cell growth
    inhibition was 43.0 mg/L permethrin and the IC50 for protein
    synthesis was 43.0 mg/L permethrin (DOSE, 1997).

    Permethrin did not cause chromosomal loss in  Drosophilia 
     melanogaster and did not increase chromosomal aberrations in rat
    bone marrow cells  in vitro (DOSE, 1997).

    Fish toxicity

    Permethrin 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 (48 hr) for rainbow trout and bluegill sunfish are 5.4 and 1.8
    µg/L permethrin respectively (DOSE, 1997).

    LC50 (96 hr) for channel catfish, largemouth bass, brook trout and
    desert pupfish are 1.1, 8.5, 3.2 and 5.0 µg/L permethrin respectively
    (DOSE, 1997).

    Permethrin in concentrations of 1.25, 2.5, 5.0, 10, 20 and 40 µg/L had
    no effect on embryo survival of sheepshead minnow; fry were unaffected
    by permethrin 10 µg/L but only 19 per cent survived at 20 µg/L (DOSE,
    1997).

    EC Directive on Drinking Water Quality 80/778/EEC

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

    AUTHORS

    SA Cage MSc M Inst Inf Sci
    SM Bradberry BSc MB MRCP
    S Meacham BSc
    JA Vale MD FRCP FRCPE FRCPG FFOM

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

    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
    28/1/98

    REFERENCES

    Abou-Donia MB, Wilmarth KR, Jensen KF, Oehme FW, Kurt TL.
    Neurotoxicity resulting from coexposure to pyridostigmine bromide,
    DEET, and permethrin: Implications of Gulf War chemical exposures.
    J Toxicol Environ Health 1996; 48: 35-56.

    Adamis Z, Antal A, Füzesi I, Molnár J, Nagy L, Susán M.
    Occupational exposure to organophosphorus insecticides and synthetic
    pyrethroid.
    Int Arch Occup Environ Health 1985; 56: 299-305.

    Advisory Committee on Pesticides.
    Evaluation number 55: Esfenvalerate.
    London: Ministry of Agriculture Fisheries and Food, 1992.

    Akhtar N, Kayani SA, Ahmad MM, Shahab M.
    Insecticide-induced changes in secretory activity of the thyroid gland
    in rats.
    J Appl Toxicol 1996; 16: 397-400.

    Aldridge WN, Clothier B, Forshaw P, Johnson MK, Parker VH, Price RJ,
    Skilleter DN, Verschoyle RD, Stevens C.
    The effect of DDT and the pyrethroid cismethrin and decamethrin on the
    acetyl choline and cyclic nucleotide content of rat brain.
    Biochem Pharmacol 1978; 27: 1703-6.

    Aldridge WN.
    An assessment of the toxicological properties of pyrethroids and their
    neurotoxicity.
    Crit Rev Toxicol 1990; 21(2): 89-104.

    Barrueco C, Herrera A, Caballo C, de la Pena E.
    Cytogenetic effects of permethrin in cultured human lymphocytes.
    Mutagenesis 1992; 7: 433-7.

    Barrueco C, Herrera A, Caballo C, de la Peńa E.
    Induction of structural chromosome aberrations in human lymphocyte
    cultures and CHO cells by permethrin.
    Teratogenesis Carcinog Mutagen 1994; 14: 31-8.

    Blaylock BL, Abdel Nasser M, McCarty SM, Knesel JA, Tolson KM,
    Ferguson PW, Mehendale HM.
    Suppression of cellular immune responses in BALB/c mice following oral
    exposure to permethrin.
    Bull Environ Contam Toxicol 1995; 54: 768-74.

    BNF.
    Joint Formulary Committee, 1997-98.
    British National Formulary. Number 34 (September 1997).
    London: British Medical Association and the Royal Pharmaceutical
    Society of Great Britain, 1997.

    Box SA, Lee MR.
    A systemic reaction following exposure to a pyrethroid insecticide.
    Hum Exp Toxicol 1996; 15: 389-90.

    Bradbury JE, Forshaw PJ, Gray AJ, Ray DE.
    The action of mephenesin and other agents on the effects produced by
    two neurotoxic pyrethroids in the intact and spinal rat.
    Neuropharmacology 1983; 22: 907-14.

    Bradbury SP, Coats JR.
    Comparative toxicology of the pyrethroid insecticides.
    Rev Environ Contam Toxicol 1989; 108: 133-77.

    Brandenburg K, Deinard AS, DiNapoli J, Englender SJ, Orthoefer J,
    Wagner D.
    1% permethrin cream rinse vs 1% lindane shampoo in treating
    pediculosis capitis.
    Am J Dis Child 1986; 140: 894-6.

    Casida JE, Gammon DW, Glickman AH, Lawrence LJ.
    Mechanisms of selective action of pyrethroid insecticides.
    Annu Rev Pharmacol Toxicol 1983; 23: 413-38.

    Chen S, Zhang Z, He F, Yao P, Wu Y, Sun J, Liu L, Li Q.
    An epidemiological study on occupational acute pyrethroid poisoning in
    cotton farmers.
    Br J Ind Med 1991; 48: 77-81.

    Chester G, Hatfield LD, Hart TB, Leppert BC, Swaine H, Tummon OJ.
    Worker exposure to, and absorption of cypermethrin during aerial
    application of an "ultra low volume" formulation to cotton.
    Arch Environ Contam Toxicol 1987; 16: 69-78.

    Clark JM, Marion JR.
    Enhanced neurotransmitter release by pyrethroid insecticides.
    In: Narahashi T, Chambers JE, eds. Insecticide action: from molecule
    to organism.
    Plenum Press, 1989; 139-68.

    Desi I, Palotas M, Vetro G, Csolle I, Nehez M, Zimanyi M, Ferke A,
    Huszta E, Nagymajtenyi L.
    Biological monitoring and health surveillance of a group of greenhouse
    pesticide sprayers.
    Toxicol Lett 1986; 33: 91-105.

    DiNapoli JB, Austin RD, Englender SJ, Gomez MP, Barrett JF.
    Eradication of head lice with a single treatment.
    Am J Public Health 1988; 78: 978-80.

    Dolara P, Salvadori M, Capobianco T, Torricelli F.
    Sister-chromatid exchanges in human lymphocytes induced by dimethoate,
    omethoate, deltamethrin, benomyl and their mixture.
    Mutat Res 1992; 283: 113-8.

    Dorman DC, Beasley VR.
    Neurotoxicology of pyrethrin and the pyrethroid insecticides.
    Vet Hum Toxicol 1991; 33: 238-43.

    DOSE/Dictionary of substances and their effects. (CD-ROM).
    Cambridge: Royal Society of Chemistry, 1997.

    Eadsforth CV, Bragt PC, van Sittert NJ.
    Human dose-excretion studies with pyrethroid insecticides cypermethrin
    and alphacypermethrin: relevance for biological monitoring.
    Xenobiotica 1988; 18: 603-14.

    EC Directive.
    EC Directive relating to the quality of water intended for human
    consumption, 80/778/EEC.
    Luxembourg: Office for Official Publications of the European
    Communities, 1980.

    Eells JT, Bandettini PA, Holman PA, Propp JM.
    Pyrethroid insecticide-induced alterations in mammalian synaptic
    membrane potential.
    J Pharmacol Exp Ther 1992; 262: 1173-81.

    Eil C, Nisula BC.
    The binding properties of pyrethroids to human skin fibroblast
    androgen receptors and to sex hormone binding globulin.
    J Steroid Biochem 1990; 35: 409-14.

    Flannigan SA, Tucker SB, Key MM, Ross CE, Fairchild EJ, Grimes BA,
    Harrist RB.
    Synthetic pyrethroid insecticides: a dermatological evaluation.
    Br J Ind Med 1985; 42: 363-72.

    Flannigan SA, Tucker SB.
    Topical indomethacin for synthetic pyrethroid exposure.
    Contact Dermatitis 1984; 11: 55-6.

    Flannigan SA, Tucker SB.
    Variation in cutaneous sensation between synthetic pyrethroid
    insecticides.
    Contact Dermatitis 1985a; 13: 140-7.

    Flannigan SA, Tucker SB.
    Variation in cutaneous perfusion due to synthetic pyrethroid exposure.
    Br J Ind Med 1985b; 42: 773-6.

    Forshaw PJ, Ray DE.
    Development of therapy for type II pyrethroid insecticide poisoning.
    Hum Exp Toxicol 1997; 16: 382.

    Gammon DW, Lawrence LJ, Casida JE.
    Pyrethroid toxicology: protective effects of diazepam and
    phenobarbital in the mouse and the cockroach.
    Toxicol Appl Pharmacol 1982; 66: 290-6.

    Grant SMB.
    An unusual case of burning mouth sensation.
    Br Dent J 1993; 175: 378-80.

    He F, Sun J, Han K, Wu Y, Yao P, Wang S, Liu L.
    Effects of pyrethroid insecticides on subjects engaged in packaging
    pyrethroids.
    Br J Ind Med 1988; 45: 548-51.

    He F, Wang S, Liu L, Chen S, Zhang Z, Sun J.
    Clinical manifestations and diagnosis of acute pyrethroid poisoning.
    Arch Toxicol 1989; 63: 54-8.

    He F, Zhang Z, Chen S, Sun J, Yao P, Liu L, Li Q.
    Effects of combined exposure to pyrethroids and methamidophos on
    sprayers.
    Arch Complex Environ Stud 1990; 2: 31-6.

    He F, Deng H, Ji X, Zhang Z, Sun J, Yao P.
    Changes of nerve excitability and urinary deltamethrin in sprayers.
    Int Arch Occup Environ Health 1991; 62: 587-90.

    He F.
    Synthetic pyrethroids.
    Toxicology 1994; 91: 43-9.

    Health and Safety Executive.
    EH40/95: Occupational exposure limits 1995.
    Sudbury: Health and Safety Executive, 1995.

    Herrera A, Barrueco C, Caballo C, Pena E.
    Effect of permethrin on the induction of sister chromatid exchanges
    and micronuclei in cultured human lymphocytes.
    Environ Mol Mutagen 1992; 20: 218-22.

    Hiromori T, Nakanashi T, Kawaguchi S, Sako H, Suzuki T, Miyamoto J.
    Therapeutic effects of methocarbamol on acute intoxication by
    pyrethroids in rats.
    J Pestic Sci 1986; 11: 9-14.

    HSDB/Hazardous Substances Data Bank.
    In: Tomes plus. Environmental Health and Safety Series I. CD-ROM. Vol
    35.
    Washington DC: National Library of Medicine, 1997.

    Hutson DH.
    The metabolic fate of synthetic pyrethroid insecticides in mammals.
    In: Bridges JW, Chasseaud LF, eds. Progress in drug metabolism.
    New York: John Wiley & Sons, 1979; 215-52.

    IARC/International Agency for Research on Cancer.
    Permethrin.
    IARC Monographs on the Evaluation of the Carcinogenic Risk of
    Chemicals to Humans 1991; 53: 329-49.

    IPCS/International Programme on Chemical Safety.
    Environmental health criteria 87. Allethrins: allethrin, d-allethrin,
    bioallethrin, s-bioallethrin.
    Geneva: World Health Organization, 1989a.

    IPCS/International Programme on Chemical Safety.
    Environmental health criteria 92. Resmethrins: resmethrin,
    bioresmethrin, cismethrin.
    Geneva: World Health Organization, 1989b.

    IPCS/International Programme on Chemical Safety.
    Environmental health criteria 82. Cypermethrin.
    Geneva: World Health Organization, 1989c.

    IPCS/International Programme on Chemical Safety.
    Environmental health criteria 99. Cyhalothrin.
    Geneva: World Health Organization, 1990a.

    IPCS/International Programme on Chemical Safety.
    Environmental health criteria 94. Permethrin.
    Geneva: World Health Organization, 1990b.

    IPCS/International Programme on Chemical Safety.
    Environmental health criteria 95. Fenvalerate.
    Geneva: World Health Organization, 1990c.

    IPCS/International Programme on Chemical Safety.
    Environmental health criteria 97. Deltamethrin.
    Geneva: World Health Organization, 1990d.

    IPCS/International Programme on Chemical Safety.
    Environmental health criteria 98. Tetramethrin.
    Geneva: World Health Organization, 1990e.

    IPCS/International Programme on Chemical Safety.
    Environmental health criteria 96. d-phenothrin.
    Geneva: World Health Organization, 1990f.

    Kalter DC, Sperber J, Rosen T, Matarasso S.
    Treatment of pediculosis pubis. Clinical comparison of efficacy and
    tolerance of 1% lindane shampoo vs 1% permethrin creme rinse.
    Arch Dermatol 1987; 123: 1315-9.

    Kaul PP, Rastogi A, Hans RK, Seth TD, Seth PK, Srimal RC.
    Fenvalerate-induced alterations in circulatory thyroid hormones and
    calcium stores in rat brain.
    Toxicol Lett 1996; 89: 29-33.

    Knox JM, Tucker SB, Flannigan SA.
    Paresthesia from cutaneous exposure to a synthetic pyrethroid
    insecticide.
    Arch Dermatol 1984; 120: 744-6.

    Knox JM, Tucker SB.
    A new cutaneous sensation caused by synthetic pyrethroids.
    Clin Res 1982; 30: 915a.

    Kolmodin-Hedman B, Swensson A, Akerblom M.
    Occupational exposure to some synthetic pyrethroids (permethrin and
    fenvalerate).
    Arch Toxicol 1982; 50: 27-33.

    Kolmodin-Hedman B, Akerblom M, Flato S, Alex G.
    Symptoms in forestry workers handling conifer plants treated with
    permethrin.
    Bull Environ Contam Toxicol 1995; 55: 487-93.

    Le Quesne PM, Maxwell IC, Butterworth STG.
    Transient facial sensory symptoms following exposure to synthetic
    pyrethroids: A clinical and electrophysiological assessment.
    Neurotoxicology 1980; 2: 1-11.

    Leahey JP.
    Metabolism and environmental degradation.
    In: Leahey JP, ed. The pyrethroid insecticides.
    London: Taylor & Francis, 1985; 263-342.

    Leclercq M, Cotonat J, Foulhoux P.
    Recherche d'un antagonisme ŕ l'intoxication par la deltaméthrine.
    J Toxicol Clin Exp 1986; 6: 85-93.

    Lessenger JE.
    Five office workers inadvertently exposed to cypermethrin.
    J Toxicol Environ Health 1992; 35: 261-7.

    Lisi P.
    Sensitization risk of pyrethroid insecticides.
    Contact Dermatitis 1992; 26: 349-50.

    Llewellyn DM, Brazier A, Brown R, Cocker J, Evans ML, Hampton J,
    Nutley BP, White J.
    Occupational exposure to permethrin during its use as a public hygiene
    insecticide.
    Ann Occup Hyg 1996; 40: 499-509.

    Mauck WL, Olson LE, Marking LL.
    Toxicity of natural pyrethrins and five pyrethroids to fish.
    Arch Environ Contam Toxicol 1976; 4: 18-29.

    McCain WC, Lee R, Johnson MS, Whaley JE, Ferguson JW, Beall P, Leach
    G.
    Acute oral toxicity study of pyridostigmine bromide, permethrin, and
    DEET in the laboratory rat.
    J Toxicol Environ Health 1997; 50: 113-24.

    Miyamoto J, Kaneko H, Tsuji R, Okuno Y.
    Pyrethroids, nerve poisons: How their risks to human health should be
    assessed.
    Toxicol Lett 1995; 82-83: 933-40.

    Narahashi T.
    The role of ion channels in insecticide action. In: Narahashi T,
    Chambers JE, eds. Insecticide action: from molecule to organism.
    Plenum Press, 1989; 55-84.

    Narahashi T, Carter DB, Frey J, Ginsburg K, Hamilton BJ, Nagata K, Roy
    ML, Song J-H, Tatebayashi H.
    Sodium channels and GABAA receptor-channel complex as targets of
    environmental toxicants.
    Toxicol Lett 1995; 82-83: 239-45.

    Narahashi T.
    Neuronal ion channels as the target sites of insecticides.
    Pharmacol Toxicol 1996; 78: 1-14.

    Nassif M, Brooke JP, Hutchinson DBA, Kamel OM, Savage EA.
    Studies with permethrin against bodylice in Egypt.
    Pestic Sci 1980; 11: 679-84.

    Newton JG, Breslin ABX.
    Asthmatic reactions to a commonly used aerosol insect killer.
    Med J Aust 1983; 1: 378-80.

    Oortgiesen M, van Kleef RGDM, Vijverberg HPM.
    Block of deltamethrin-modified sodium current in cultured mouse
    neuroblastoma cells: local anesthetics as potential antidotes.
    Brain Res 1990; 518: 11-8.

    Pesticides 1997.
    Ministry of Agriculture, Fisheries and Food (MAFF) and the Health and
    Safety Executive (HSE).
    Pesticides 1997. Pesticides approved under the control of pesticides
    regulations 1986.
    London: Her Majesty's Stationary Office, 1997.

    Pesticide Manual.
    Tomlin CDS, ed.
    The Pesticide Manual.
    London: The British Crop Protection Council, 1997.

    Peter JV, John G, Cherian AM.
    Pyrethroid poisoning.
    J Assoc Physicians India 1996; 44: 343-344.

    Puig M, Carbonell E, Xamena N, Creus A, Marcos R.
    Analysis of cytogenetic damage induced in cultured human lymphocytes
    by the pyrethroid insecticides cypermethrin and fenvalerate.
    Mutagenesis 1989; 4: 72-4.

    Ray DE.
    Pesticides derived from plants and other organisms. 13.2 Pyrethrum and
    related compounds.
    In: Hayes WJ, Jr., Laws ER, Jr. eds. Handbook of pesticide toxicology.
    Vol 2.
    San Diego, California: Academic Press, 1991; 585-636.

    Reprotox.
    In: Tomes plus. Environmental Health and Safety Series I. CD-ROM. Vol
    35.
    Washington DC: Fabro S, Scialli AR. Reproductive Toxicology Center,
    Columbia Hospital for Women, 1997.

    RTECS.
    Registry of Toxic Effects of Chemical Substances.
    In: Tomes plus. Environmental Health and Safety Series I. CD-ROM. Vol
    35.
    Washington DC: National Institute for Occupational Safety and Health
    (NIOSH), 1997.

    Soderlund DM, Bloomquist JR.
    Neurotoxic actions of pyrethroid insecticides.
    Annu Rev Entomol 1989; 34: 77-96.

    Soderlund DM, Casida JE.
    Effects of pyrethroid structure on rates of hydrolysis and oxidation
    by mouse liver microsomal enzymes.
    Pestic Biochem Physiol 1977; 7: 391-401.

    Song J-H, Nagata K, Tatebayashi H, Narahashi T.
    Interactions of tetramethrin, fenvalerate and DDT at the sodium
    channel in rat dorsal root ganglion neurons.
    Brain Res 1996; 708: 29-37.

    Song J-H, Narahashi T.
    Selective block of tetramethrin-modified sodium channels by (+/-)-
    alpha-tocopherol (vitamin E).
    J Pharmacol Exp Ther 1995; 275: 1402-11.

    Song J-H, Narahashi T.
    Modulation of sodium channels of rat cerebellar Purkinje neurons by
    the pyrethroid tetramethrin.
    J Pharmacol Exp Ther 1996; 277: 445-53.

    Surrallés J, Xamena N, Creus A, Catalán J, Norppa H, Marcos R.
    Induction of micronuclei by five pyrethroid insecticides in
    whole-blood and isolated human lymphocyte cultures.
    Mutat Res Genet Toxicol 1995; 341: 169-84.

    The UK Pesticide Guide.
    Whitehead R, ed. Centre for Agriculture and Biosciences (CAB)
    International and the British Crop Protection Council.
    The UK Pesticide Guide.
    Cambridge: University Press, 1997.

    Trainer VL, McPhee JC, Boutelet-Bochan H, Baker C, Scheuer T, Babin D,
    Demoute J-P, Guedin D, Catterall WA.
    High affinity binding of pyrethroids to the alpha subunit of brain
    sodium channels.
    Mol Pharmacol 1997; 51: 651-7.

    Tucker SB, Flannigan SA, Smolensky MH.
    Comparison of therapeutic agents for synthetic pyrethroid exposure.
    Contact Dermatitis 1983; 9: 316.

    Tucker SB, Flannigan SA, Ross CE.
    Inhibition of cutaneous paresthesia resulting from synthetic
    pyrethroid exposure.
    Int J Dermatol 1984; 23: 686-9.

    Tucker SB, Flannigan SA.
    Cutaneous effects from occupational exposure to fenvalerate.
    Arch Toxicol 1983; 54: 195-202.

    van der Rhee HJ, Farquhar JA, Vermeulen NPE.
    Efficacy and transdermal absorption of permethrin in scabies patients.
    Acta Derm Venereol 1989; 69: 170-82.

    Vijverberg HPM, van den Bercken J.
    Action of pyrethroid insecticides on the vertebrate nervous system.
    Neuropathol Appl Neurobiol 1982; 8: 421-40.

    Vijverberg HPM, van den Bercken J.
    Neurotoxicological effects and the mode of action of pyrethroid
    insecticides.
    Crit Rev Toxicol 1990; 21: 105-26.

    Wilkes MF, Woollen BH, Marsh JR, Batten PL, Chester G.
    Biological monitoring for pesticide exposure - the role of human
    volunteer studies.
    Int Arch Occup Environ Health 1993; 65: S189-92.

    Woollen BH, Marsh JR, Chester G.
    Metabolite profiles of a pyrethroid insecticide following oral and
    dermal absorption in man.
    Proceedings of a Conference on Percutaneous Penetration 1991; 10-12
    April 1991: 20-5.

    Woollen BH, Marsh JR, Laird WJD, Lesser JE.
    The metabolism of cypermethrin in man: differences in urinary
    metabolite profiles following oral and dermal administration.
    Xenobiotica 1992; 22: 983-91.

    Woollen BH.
    Biological monitoring for pesticide absorption.
    Ann Occup Hyg 1993; 37: 525-40.

    Zhang Z, Sun J, Chen S, Wu Y, He F.
    Levels of exposure and biological monitoring of pyrethroids in
    spraymen.
    Br J Ind Med 1991; 48: 82-6.