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    CYHEXATIN

    EXPLANATION

         Cyhexatin was reviewed by the JMPR in 1970, 1973, 1974, 1975,
    1977, 1978, 1979, 1982, 1983 and 1985 (Annex 1, FAO/WHO 1971a,
    1974a, 1975a, 1976a, 1978a, 1979a, 1980a, 1983a, 1984, 1986a).  An
    ADI of 0.008 mg/kg bw was allocated in 1980.  A teratology study in
    the New Zealand White rabbits at dose levels of 0.75 and 3 mg/kg
    bw/day and a multi-generation study in rats (top dose level 100 ppm)
    considered in 1970 did not demonstrate biological effects.  Since
    the evaluation in 1985, cyhexatin has been withdrawn from use as an
    acaricide in a number of countries as a result of new teratology
    studies.  The 1988 meeting was requested to evaluate these studies
    but insufficient data were available at that time.  These data and
    other teratology studies have now been submitted and reviewed.

    Short-term studies

    Rabbits

         Groups of 4 virgin female hybrid Hy/Cr White New Zealand
    rabbits were given doses of 96% pure cyhexatin (technical) of 0,
    0.5, 1.0 or 3.0 mg/kg bw/day by gavage for 13 days.  Dosing volume
    was 5 ml/kg bw of a suspension of the test material in a 0.5 aqueous
    solution of carboxymethyl cellulose.  Suspensions were prepared
    weekly. The rabbits were housed individually and monitored daily for
    condition and behaviour; body weight and food consumption were
    recorded weekly. On day 13 blood samples were taken two hours
    post-dosing and fecal samples were obtained.  On Day 14 the animals
    were sacrificed and necropsied and samples of liver, kidney and
    ovary saved for analysis.

         There were no effects noted on appearance, behaviour or gross
    pathology.  Body weights, liver, kidney and ovary weights and food
    consumption were similar in all groups.  Tissues analyses results
    indicated dose-related increases in blood, liver, kidney and fecal
    tin concentrations.  No effect was observed in ovary (Monnot  et al.
    1989a).

         Groups of 4 virgin female rabbits of the same strain as in the
    oral study were given daily dermal doses of 0, 0.5, 12.0 or 3.0 mg
    cyhexatin (96%)/kg bw for 13 days.  Dose volume was 0.25 ml/kg bw of
    suspensions in 0.5 aqueous carboxymethyl cellulose solutions.  The
    suspensions were applied to the shaved back of each rabbit at sites
    which were not treated more than twice without an interval of at
    least seven days.  At application the site was given a slight
    massage for about one minute.  The rabbits were monitored for
    clinical conditions, effects at application site, body weights and
    food consumption.  Blood, fecal and tissue samples were taken
    similarly to the oral study.

         There were no effects on appearance, behaviour or gross
    pathology.  There was a dose-related increase in the incidence of
    erythema at all dose levels.  Desquamation and atonia were observed
    at all treated sites with no dose-relationship but with a slight
    increase with time.  "Cracking" of the skin was observed in one
    rabbit at 1 mg/kg bw and 3 at 3 mg/kg bw.  At 3 mg/kg bw no increase
    in body weight was observed in contrast to weight gains in controls
    and the rabbits in the other two groups with the exception of one
    rabbit in the 0.5 mg/kg bw group which lost weight;  however, this
    rabbit was stated to have been delivered on Day 9 of the treatment
    and, thus, was not comparable to the rest of the animals.  Food
    consumption was slightly lower in the second week in 2 rabbits at
    the 3 mg/kg bw level. No effects were noted on liver, kidney or
    ovary weights.  Tissue tin levels tended to be variable between
    animals.  Mean levels of tin were increased with dose in liver,
    feces and, very slightly, in blood.  Fecal levels were higher in
    this study than in the preceding oral study (Monnot  et al. 1989b). 

    Special studies on teratology

    Oral studies

    Rat

         Groups of 30 female Sprague-Dawley derived Charles River COBS
    CD rats (Portage, Michigan, USA) were mated (1:1 basis) at 84 days
    of age.  The day a copulatory plug was observed was designated
    Gestation Day 0.  On Days 6-15 of gestation the females were given
    doses of cyhexatin (95.6% pure) of 0, 0.5, 1.0 or 5.0 mg/kg bw/day
    by gavage.  The test material was suspended in corn oil for
    administration with the dose level adjusted to correct for purity. 
    The dosing suspensions were prepared once for the study and agitated
    with a magnetic stirrer during dose administrations.  Dose volume
    was 2.0 ml/kg.  The animals were monitored during the study for
    signs of toxicity, body weight, food and water consumption.  On Day
    20 of gestation the females were sacrificed and the uterus and ovary
    examined.  Other organs were examined for gross pathology.  Fetuses
    were weighed, sexed and examined for external malformations.  Half
    the fetuses were examined for visceral malformations and the other
    half for skeletal malformations.

         There were no clinical signs of toxicity and no treatment-
    related gross pathology.  During dosing the 5 mg/kg bw group had
    slightly lower body weight gains and food consumption but overall
    weight gain did not differ between groups and the differences were
    not considered to be biologically significant. There were no
    treatment-related effects on water consumption, number of fetuses
    and viable fetuses per dam, number of resorptions (all early), or
    fetal body weight or sex ratio.  Absolute and relative liver weights
    and mean gravid uterus weight were higher in the 5 mg/kg bw group. 
    The total incidence of malformations was 4(3), 3(2), 2(2) and 6(6)

    fetuses (litters) at 0, 0.5, 1.0 and 5.0 mg/kg bw, respectively. 
    Microphthalmia was observed only in treated animals in 1, 2, and
    2(2) fetuses at 0.5, 1.0 and 5.0 mg/kg bw, respectively.  This
    malformation was not listed in the submitted historical control data
    for 35 studies.  Tail anomalies (short; short and thread-like; or
    short and bent) were observed in 1, 0, 1 and 3(3) fetuses (litters)
    at 0, 0.5, 1.0 and 5.0 mg/kg bw, respectively.  The other malformed
    fetus at 5 mg/kg bw had fused skull bones.  The mid- and low dose
    fetuses with microphthalmia both had (multiple defects including
    cleft palate (both), cleft lip (0.5 mg/kg bw), micrognathia
    (1.0 mg/kg bw) and malformed skull bones (1.0 mg/kg bw).  These
    other anomalies were not observed at 5.0 mg/kg bw.  Visceral
    anomalies were observed only in control and low dose fetuses. 
    Development variations were observed in some fetuses in each group; 
    however, the occurrence of 25 or 27 pre sacral vertebrae was
    observed only at 5.0 mg/kg bw in 6(6) fetuses (litters).  Although
    the incidence of malformations was slightly higher in the high dose
    group, it cannot be considered to be indicative of a teratogenic
    effect.  However, the vertebral variations of 5.0 mg/kg bw suggest a
    fetototoxic effect.  The NOAEL for this study is considered to be
    1.0 mg/kg bw (Aldridge  et al. 1986).

    Rabbit

         In a teratology probe study, groups of 7 female New Zealand
    White rabbits (Hazleton-Dutchland) was artificially inseminated and
    then dosed with 0, 5, 10 or 20 mg cyhexatin/kg bw/day on Days 6-18
    of gestation (Day of insemination = Day 0).  The test material was
    suspended in corn oil at concentrations to provide the appropriate
    doses in 1 ml/kg bw and administered with a 4-inch 12 gauge dosing
    needle.  One analysis of each solution is stated to indicate
    concentrations of 99-103% of target.  There were 2, 7 and 7 deaths
    at 5, 10 and 29 mg/kg bw, respectively, during the dosing period. 
    Autopsy revealed lesions in the trachea and lungs of all animals
    that died suggesting that improper dosing technique contributed to
    the deaths.  Two animals each at 10 and 20 mg/kg and all 5 surviving
    animals at 5 mg/kg bw had stomach erosions or ulcers.  Four of the 5
    surviving animals at 5 mg/kg bw had only resorptions (Berdasco
     et al. 1986).

         A second probe was carried out in the same strain of rabbits
    prepared for treatment as above (7 rabbits/dose level) but dosed
    with 0, 1, 5 or 10 mg cyhexatin/kg bw/day on Days 7-19 of gestation. 
    In this study the test material was suspended in 0.5% aqueous
    Methocel at concentrations to provide the appropriate doses in
    1 ml/kg bw and administered with a # 10 juvenile Foley catheter. One
    analysis of each solution indicated concentrations of 80-101% of
    target.  Again, deaths were observed only in treated groups with 2,
    1 and 1 deaths at 1, 5 and 10 mg/kg bw.  Tracheal and lung lesions
    were not seen in this study.  Stomach erosion/ulcers were observed
    in one animal at 5 mg/kg bw and 4 at 10 mg/kg bw.  Peritoneal blood

    was observed in 4 females at 10 mg/kg bw and was considered to be
    evidence of recent abortion.  Body weight gains were reduced at both
    5 and 10 mg/kg bw/day.  At 10 mg/kg bw, 4 females totally resorbed
    and/or aborted their fetuses.  Both of the other surviving females
    had resorptions and the number of viable fetuses was significantly
    reduced compared to controls.  At 5 mg/kg bw, there was an increased
    incidence of resorptions, with one litter totally resorbed, and a
    decreased number of fetuses.  The 1 mg/kg bw group was similar to
    controls (Berdasco  et al. 1986).

         As a result of the above probe studies, the teratology study
    was conducted in groups of 20 females of the same strain of rabbit
    (5 months old at insemination) with dose levels of 0, 0.5, 1.0 and
    3.0 mg cyhexatin (95.5%)/kg bw/day given Days 7-19 of gestation (Day
    of artificial insemination = Day 0 of gestation) as a suspension in
    0.5% aqueous Methocel (1 ml/kg bw) and administered with 5 cc
    plastic syringes and 16 inch long flexible feeding tubes. The
    suspensions of test material were prepared once (concentration
    adjusted for purity of test material) and resuspended daily with a
    Brinkman polytron homogenizer and maintained in suspension during
    treatment with a magnetic stirrer.  Analyses of the suspensions at
    intervals during the study indicated sample concentrations of
    70-104%, 91-125% and 55-137% of target at the 0.5, 1.0 and 3.0 mg/kg
    bw dose levels, suggesting that homogeneity was difficult to attain
    especially at the highest concentration.  The homogeneity problems
    may have related to the particle size of the cyhexatin used in the
    suspension but no data were available for this parameter.  The
    rabbits were housed individually in suspended wire cages and
    maintained on Purina Certified Rabbit Chow # 5322 and tap water
    available  ad libitum.  The rabbits were monitored throughout the
    study for clinical condition and body weight.  Females which died or
    which aborted or delivered prematurely were autopsied.  On Day 29,
    all surviving females were sacrificed and the uterus and ovary of
    each examined.  Fetuses were weighed, sexed and examined for
    external, visceral and skeletal malformations and variations.

         There were no treatment-related effects on mortality (1-4
    females/group died, all but one of which (low dose) animals showed
    red fluid in the thoracic cavity which may indicate injury during
    dosing), or general signs of toxicity. Five rabbits aborted: one at
    0.5 mg/kg bw and 4 at 3.0 mg/kg bw; two rabbits delivered on Day 28:
    one each at 1.9 and 3.0 mg/kg bw; and two rabbits totally resorbed
    their litters: one each at 0.5 and 3.0 mg/kg bw.  Body weight
    changes were extremely variable in all groups and did not appear to
    be related to treatment.  Food intakes were not measured.  Liver to
    body weight ratios were not dose-related and there were no gross
    pathological lesions indicative of a treatment-related effect.  The
    number of viable fetuses per dam was reduced in the 3.0 mg/kg bw
    group.  The number of dams with resorptions did not differ between
    groups but the number of dams with two or more resorptions was
    increased at 3.0 mg/kg bw.  Total percent post-implanatation loss

    was increased in a dose-related manner and was 2x and 3x the control
    value of 1.0 and 3.0 mg/kg bw, respectively.  Fetal body weights and
    sex ratio were not affected by treatment. A few fetuses in each
    group had malformations but the only observation which appeared to
    be dose-related was hydrocephalus in 8(4) fetuses (litters) at
    3.0 mg/kg bw.  In this group, one aborted fetus had a dome-shaped
    head but was not examined viscerally.  The variability of results
    and lack of dose relationships may have been related either to the
    questionable homogeneity of the test or to maternal infection. 
    There was no consistent evidence of maternal toxicity in this study. 
    The NOAEL for this study was 0.5 mg/based on increased
    post-implantation loss at the nominal 1.0 mg/kg bw level (Schardein
     et al. 1986).

         To confirm the results of the above study, another study was
    conducted in a different laboratory with groups of 27 artificially
    inseminated New Zealand White (Hazleton-Dutchland) female rabbits. 
    The test material, technical cyhexatin of 94.8-95.5% purity, was
    suspended in 0.5 aqueous Methocel at concentrations to provide doses
    of 0.75 or 3.0 mg/kg bw in a volume of 1 ml/kg bw.  Again, no data
    were available on particle size of the cyhexatin.  No analyses of
    administered suspensions were reported.  Controls received 0.5%
    aqueous Methocel at the same volume.  The suspensions were prepared
    once and were maintained with continuous magnetic stirring
    throughout the study (Hanley, 1989).  Analyses pre- and post-test
    indicate concentrations were 89-106% of target.  The suspensions of
    cyhexatin were given by oral gavage Days 7 through 19 of gestation
    (Day of insemination = Day 0 of gestation).  The rabbits were housed
    singly and maintained on Purina Rabbit Chow (8 oz/day) and tap water
     (ad libitum).  The type of cages and the room conditions are not
    described.  Body weights and clinical condition of the rabbits were
    monitored throughout the study.  On Day 28 of gestation, Cesarian
    sections were performed on all rabbits and the uterus of each was
    weighted and examined.  Fetuses were weighed, sexed and examined for
    viability and external and visceral malformations.

         There were 2, 7 and 4 deaths at 0, 0.75 and 3.0 mg/kg bw,
    respectively, of which 2, 5 and 2 rabbits had lung or thoracic
    cavity lesions suggesting possible problems during dosing. 
    Abortions occurred in three rabbits at 0.75 mg/kg bw (one dam died
    after aborting one fetus) and in 12 rabbits at 3.0 mg/kg bw.  Among
    the animals that aborted at 3.0 mg/kg bw, 5 had hairballs in the
    stomach and one had slight abdominal ascites.  No significant
    pathology was observed in the other rabbits that aborted.  The
    rabbits with litters were not examined for gross pathology. 
    Individual body weight changes were quite variable but in the
    3.0 mg/kg bw most of the rabbits lost weight Days 7-10 (20/23 cf
    8/23 and 12/25 at 0 and 0.75 mg/kg bw, respectively).  During the
    remainder of the dosing period the number of females losing weight
    was slightly higher than in the other groups and the mean body
    weight change was lower than in controls.  At Day 20, mean body
    weight was statistically significantly lower in the 3.0 mg/kg bw

    group than in the controls.  This was considered to be a treatment-
    related effect.  Body weight changes in the 0.75 mg/kg bw group were
    not considered to be different than the controls.  Absolute and
    relative liver weights did not differ between the groups but there
    were only seven animals remaining at termination in the 3.0 mg/kg bw
    group.  There was an increased incidence of resorption and a
    decreased number of live fetuses in the 3.0 mg/kg bw group. 
    However, with only seven dams in this group, the significance of
    these observations is not certain. There were no apparent effects on
    fetal weights or sex ratio.  The fetuses were examined only for
    external and visceral malformations and the total incidences of any
    malformation were 3(3), 10(7) and 11(5) fetuses (litters) at 0, 0.75
    and 3.9 mg/kg bw, respectively.  The most common malformation was
    hydrocephalus with incidences of 2(2), 7(5) and 9(4) fetuses
    (litters), respectively.  Dilated cerebral ventricles were observed
    in one fetus at 0.75 and 3.0 mg/kg bw in litters with no
    hydrocephalic fetuses.  Incidences of malformations in control
    groups from 48 studies (mainly oral but some inhalation indicate
    that hydrocephalus was observed in only one of these studies (#43)
    in one fetus (of 91) (overall incidence 1/2936 fetuses and 1/839
    litters).  Dilated cerebral ventricles were observed in a total of 3
    fetuses from 2 litters (2 fetuses in study #11 and one in Study
    #16).  The incidence of this malformation is higher in the
    concurrent controls and is increased further in the treated groups. 
    At 3.0 mg/kg bw there was evidence of a maternal effect with reduced
    body weight gain during the dosing period and a high number of
    abortions.  There was no clear indication of maternal toxicity at
    0.75 mg/kg bw which may be considered to be the NOEL for maternal
    toxicity.  A NOAEL for the induction of hydrocephalus was not
    demonstrated in this study (Kirk  et al. 1989a).

         Two studies using cyhexatin from another source were carried
    out in a different laboratory.  Hybrid HY/Cr White New Zealand type
    rabbits (Charles River, France, 16-18 weeks old) were mated by the
    supplier and delivered to the laboratory on Gestation Day 1 or 2
    (Day of mating was considered Day 0 of gestation).  Groups of 24
    mated females were given doses of 0, 3.0 (technical) or 3.0 (pure)
    mg/kg bw/day in the first study and 0, 0.5, 0.75 or 1.0 mg
    (technical)/kg bw/day in the second study on Days 6-18 of gestation. 
    Purity of the technical test material was 96% and no adjustment was
    made for purity when the dosing suspensions were prepared weekly in
    0.5% aqueous carboxymethyl cellulose at concentrations to provide
    the appropriate doses in a volume of 5 ml/kg bw.  The suspensions
    were stated to have been "under constant agitation before and during
    daily dosing".  No analyses for homogeneity were performed. 
    Particle size of the cyhexatin was 20-50 microns for technical
    material and 20-60 microns for the pure material prior to
    suspension.  The animals were dosed by intragastric intubation
    (details of method not given).  The rabbits were housed individually
    in plastic cages and were given access to 200 g of pelleted rabbit
    diet (UAR-112-Usine d'Alimentation Rationnelle)/day.  Tap water was

    available  ad libitum.  The animals were monitored for clinical
    signs, body weight and food consumption throughout the study. 
    Animals which died or aborted were autopsied.  All surviving females
    were sacrificed on Day 29 and the ovary and uterine contents
    examined.  The number, sex, and body weights of fetuses were
    recorded and the fetuses were examined for external visceral and
    skeletal malformations.  The heads of half the fetuses were removed
    for sectioning.

         There were 1-3 deaths in each group of rabbits (except the
    group given pure cyhexatin in which there were no deaths) but the
    incidence was not dose-or treatment-related.  In the first study
    three rabbits aborted in the group given technical material
    (3.0 mg/kg bw) but none in the controls or those given pure
    cyhexatin.  In the second study abortions were observed only in the
    controls (3) and 0.5 mg/kg bw (2) groups.  None of the rabbits
    delivered prematurely and none resorbed their entire litter.  Body
    weights and food consumptions were somewhat variable but differences
    did not appear to be related to treatment.  There were no apparent
    treatment-related effects on numbers of viable fetuses or in the
    numbers of resorptions.  The group given 3.0 mg/kg bw of pure
    cyhexatin had slightly fewer viable fetuses than the other groups as
    a result of fewer corpora lutea and implantations.  Mean fetal
    weight and sex ratio were not affected by treatment.  In each of the
    two studies, one fetus was observed with a dome-shaped head
    associated with dilated ventricles of the brain;  in the first study
    the fetus was in the 3.0 mg/kg bw technical cyhexatin group, in the
    second the fetus was in the 0.5 mg/kg bw group.  One fetus given
    pure cyhexatin at 3.0 mg/kg bw also had dilated ventricles of the
    brain but without a dome-shaped head.  The total incidence of major
    malformations was 1, 2 and 2(2) fetuses (litters) at 0, 3.0
    (technical) and 3.0 (pure) mg/kg bw/day in the first study and 1(1),
    3(3), 4(4) and 3(3) fetuses (litters) at 0, 0.5, 0.75 and 1.0 mg/kg
    bw/day in the second study.  Retinal detachment was observed in 2, 3
    and 1 fetus at 0.5, 0.75 and 1.0 mg/kg bw but was not observed in
    controls or the 3.0 mg/kg bw groups.

         In these studies there were no apparent treatment-related
    maternal toxicity, embryo/fetotoxicity, or teratogenic effects.  The
    NOAEL was the highest dose tested: 3.0 mg/kg bw (Monnot, 1989a & b).

    Dermal studies

    Rabbits

         Groups of 16 artificially inseminated New Zealand White rabbits
    (Hazleton-Dutchland, USA) were given doses of 0, 0.5, 1.0 or 3.0 mg
    cyhexatin (94.8-95.5% pure)/kg bw/day dermally on Days 7-19 of
    gestation (Day of insemination = Day 0 of gestation).  The test
    material was suspended in 0.5% aqueous Methocel at concentrations to
    provide the appropriate dose in a volume of 1 ml/kg bw.  The

    suspensions were prepared once and kept with constant agitation
    throughout the dosing period.  The test substance was applied
    uniformly to a clipped ear (about 10 x 15 cm) on the back of each
    animal and covered with an occulusive bandage and a lycra/spandex
    jacket for a 6-hour period.  The rabbits were housed individually
    and given 8 oz of Ralston Purina rabbit chow daily.  Tap water was
    available  ad libitum.  The animals were monitored throughout the
    study for clinical signs of toxicity, local effects of treatment,
    body weights and food consumption.  Cesarian section was performed
    on Day 28 of gestation and the ovary and uterine contents were
    examined.  Maternal and liver and uterine weights were recorded and
    liver and skin samples retained for histopathological examination. 
    Fetuses were examined for viability, body weight, sex and external
    and visceral malformations.  The fetuses were not examined for
    skeletal effects.

         In this study, dosing suspensions had mean concentrations of
    75.6 to 114.2% of the target.  The low mean was at the highest
    concentration in the post-dosing analyses.  There was a dose-related
    increase in lesions at the site of application (erythema/eschar,
    edema and fissuring/scaling) which increased with dosing. Fissuring
    was observed  in 0, 6, 9 and 16 rabbits at 0, 0.5, 1.0, and
    3.0 mg/kg bw, respectively, with maximum mean scores (24 hours after
    application) of 0, 1.7, 2.3 and 2.9, respectively (scale 0-4). 
    There were no clinical signs of general toxicity noted.  One rabbit
    at 0.5 mg/kg bw and two at 3.9 mg/kg bw delivered their litters
    prior to Cesarean section (Days 27, and Days 26 and 27,
    respectively).  None of the rabbits aborted.  There were no apparent
    treatment-related effects on maternal body weight gains or on liver
    weights.  Histopathological examination of the treated skin of
    rabbits given 3.0 mg/kg bw showed slight to moderate acanthosis and
    generally slight hyperkeratosis with very slight to slight
    inflammation.  There were no treatment-related effects on the number
    of fetuses or resorptions, fetal sex ratio or fetal body weights. 
    One dam in each of the control and 3.0 mg/kg bw groups had a
    hairball in the stomach, lost considerable weight during gestation
    and had fetuses with low body weights (litter means of 13.6 g and
    21.5 g, respectively).  Both of these females had runts and fetuses
    with malformations.  The total incidence of any malformation was
    8(4), 1(1), 1(1) and 8(5) in the 0, 0.5, 1.0 and 3.0 mg/kg bw
    groups, respectively.  Hydrocephalus was observed in 4(3) fetuses
    (litters) in the 3.0 mg/kg bw groups but not in any other group
    although dilated cerebral ventricles were seen in 3 fetuses from one
    control litter and one fetus in the 3.0 mg/kg bw group.  In
    contrast, dilation of the renal pelvis was observed only in controls
    in 4(3) fetuses (litters).  Multiple head and limb malformations
    (anonychia, aprosopia, brachydactyly) were observed in one control
    fetus, retroesophageal subclavian in one 0.5 mg/kg bw fetus and one
    3.0 mg/kg fetus, multiple facial anomalies (including anophthalmia)
    in one fetus at 1.0 mg/kg bw, and cleft palate and persistent
    truncus arteriosus with ventricular septal defect each in one fetus

    at 3.0 mg/kg bw.  The cleft palate occurred in a fetus with
    hydrocephalus.  Since hydrocephalus was also observed in fetuses of
    rabbits given cyhexatin orally the incidence of this lesion is
    considered to be treatment-related.  The NOAEL for teratogenicity in
    this study is 1.0 mg/kg bw. Dermal lesions at the dosing site were
    observed at all dose levels but no systemic toxicity or
    embrytoxicity was noted at any of the dose levels tested (Kirk
     et al. 1987b).

         In a similar study performed in a different laboratory with
    cyhexatin from another source, groups of 24 mated hybrid Hy/Cr New
    Zealand White female rabbits (Charles River, France) were given
    daily dermal doses of 0, 0.5, 1.0 or 3.0 mg cyhexatin (96% pure)/kg
    bw/day Days 6-18 of gestation (day of mating = Gestation Day 0). 
    The females were mated by the supplier and delivered Day 1 or 2 of
    gestation.  The test suspensions were prepared weekly in 0.5%
    aqueous carboxymethyl cellulose at concentrations (2, 4 and 12
    mg/ml) to provide the appropriate dose in a volume of 0.25 ml/kg bw. 
    The suspensions were applied to shaved areas on the backs of the
    rabbits so that test material was not applied "more than twice on
    the same site without an interval of at least seven days".  The test
    site was given a slight massage for about one minute after
    application of the test material.  It is not indicated if the site
    was occluded or if any other precautions were taken to prevent oral
    ingestion of the test material from the application site.  The
    animals were housed individually in plastic cages.  Each rabbit was
    given 200 g pelleted rabbit diet (UAR-112-Usine d'Alimentation
    Rationnelle) each day and tap water was available  ad libitum. The
    animals were monitored for clinical condition, body weight and food
    consumption throughout the study. Local effects were evaluated 24
    hours after the last application. On Gestation Day 29 the females
    were sacrificed and the ovaries and uterine contents examined. The
    numbers of implantations, numbers of live and dead fetuses, fetal
    weights and sex were recorded.  The fetuses were examined for
    external, visceral and skeletal malformations.

         The test suspensions were not analysed for achieved
    concentration or homogeneity.  There were no deaths and no gross
    signs of system toxicity in any of the groups.  Erythema, atonia and
    desquamation were observed at the treatment site of all three dose
    levels.  Cracking of the skin was observed in 6/24 rabbits at 1.0
    mg/kg bw and 11/24 rabbits at 3.0 mg/kg bw.  Mean scores for
    cracking were 0, 0, 0.3 and 0.6 on a scale of 0-3.  Edema was not
    observed in any of the rabbits.  There were no apparent treatment-
    related effects on maternal body weights or food consumption.  Two
    females aborted:  one at 0.5 mg/kg bw and one at 3.0 mg/kg bw.  No
    treatment-related effects were noted on numbers of implantations,
    resorptions or live fetuses or on fetal weights or sex.  The total
    numbers of fetuses (litters) with malformations were 3(3), 3(3),
    5(4) and 3(3) at 0, 0.5, 1.0 and 3.0 mg/kg bw, respectively. 
    Dilated ventricles of brain were observed in two fetuses: one each

    at 0.5 and 1.0 mg/kg bw.  At 1.0 mg/kg bw the fetus also had
    anasarca and cleft palate.  No fetus at 3.0 mg/kg bw had these
    malformations.  One fetus in each group including controls had
    unilateral or bilateral retinal detachment.  Skeletal malformation
    (vertebral with or without rib malformations or pelvic girdle
    malformations) were observed in 2(2), 1(1), 2(2) and 2(2) fetuses
    (litters) at 0, 0.5, 2.0 and 3.0 mg/kg bw, respectively.  The
    remaining malformed fetus at 1.0 mg/kg bw had multiple abdominal
    (visceral) and vertebral malformations.  Arthrogyposis, considered
    to be a minor defect, was observed in one fetus at 1.0 mg/kg bw and
    2 fetuses from one litter at 3.0 mg/kg bw.  Other skeletal anomalies
    and variations were observed in some fetuses in all of the groups
    and did not appear to be treatment-related.

         The only treatment-related effect observed in this study was
    local irritation at the site of application which was observed at
    all three dose levels.  The apparent NOAEL for teratogenicity in
    this study was 3.0 mg/kg bw (Monnot, 1989c).

    COMMENTS

         The oral study in Sprague-Dawley rats, utilizing dose levels of
    0.5-5.0 mg cyhexatin/kg bw/day (95.6% purity) administered on days
    6-15 of gestation did not result in any maternal toxicity or signs
    of teratogenicity.  An increased incidence of vertebral variations
    at 5 mg cyhexatin/kg bw/day was interpreted as evidence of
    fetotoxicity.

         The results of the rabbit oral teratogenicity studies available
    to the Meeting were discrepant (see Table 1).  In two cases, the
    results were negative with respect to all parameters measured, with
    NOAELs of 3 and 1 mg/kg bw/day (top doses).  In a third study, the
    NOAEL was 0.5 mg/kg bw/day based on increased post-implantation
    losses.  However, this study is of uncertain validity. The
    concentrations of test material administered varied from 70-104%,
    91-125%, and 55-137% of the nominal at 0.5, 1 and 3 mg/kg bw/day,
    respectively, suggesting non-homogeneity in the test material. 
    Hydrocephalus was observed in 8 pups from 4 litters at 3 mg/kg
    bw/day.  The distribution of these malformations raised the
    possibility that they may have been induced by infection.  The
    second positive study failed to show a NOAEL at the lowest dose
    tested (0.75 mg/kg bw/day).  This dose level caused maternal
    toxicity and hydrocephalus.  The abortion rate was high in both test
    groups (0.75 and 3 mg/kg bw/day) as was maternal mortality in all
    groups.  Again the possibility of infection cannot be ruled out.

         The existence of an additional rabbit teratology study using
    different manufacturing batches from widely separated sources was
    brought to the attention of the Meeting. This study was reported to
    be negative by the testing laboratory but was not available for
    review by the Meeting.  In view of the conflicting results in the
    positive studies, and the problems with dose levels in one of the
    studies, together with the knowledge of 3 negative studies as well
    as a completed but unreported study, the Meeting determined that
    cyhexatin should be reviewed again in 1991 when data, known to be in
    process of development, should be available.  Meanwhile, the present
    ADI remains unchanged.

    TOXICOLOGICAL EVALUATION

    Level causing no toxicological effect

         Mouse:    3 mg/kg bw/day
         Rat:      l mg/kg bw/day
         Dog:      0.75 mg/kg bw/day. 

    Estimate of acceptable daily intake

         0-0.008 mg/kg bw.

    Studies which will provide information valuable in the continued
    evaluation of the compound

    1.   Complete specifications (including nature and content of
         impurities) and physical properties of test materials used in
         all studies.

    2.   Data on absorption and tissue distribution in the pregnant
         female rabbit.

    3.   Submission of a rabbit teratology study known to exist.

    4.   Submission of a two-generation reproduction study in rats known
         to be in progress.


        TABLE 1.  TOXICOLOGICAL EVALUATION RESULTS OF RABBIT ORAL TERATOGENICITY STUDIES 

                                                                                                                               

                     EMBRYO/FETAL TOXICITY                 MATERNAL TOXICITY                    TERATOGENICITY

                                                                                                                               

                   NOAEL    LOAEL    EFFECT              NOAEL    LOAEL    EFFECT          NOAEL     LOAEL    EFFECT

    STUDY I1        0.5      1.0     Increased post       3.0      -       No effects       1.0       3.0     Hydrocephalus
                                     implantation
                                     loss

    STUDY II2       -        0.75    Abortion             0.75     3.0     Reduced          -         0.75    Hydrocephalus
                                                                           maternal
                                                                           body weight

    STUDY III3      3        -       No effect            3        -       No effect        3         -       No effect

    STUDY IV3       1        -       No effect            1        -       No effect        1         -       No effect
                                                                                                                               

    1 IRDC Laboratories
    2 Dow, USA Laboratories
    3 Hazleton, France

    TABLE 2.  ORAL (GAVAGE) TERATOLOGY STUDIES WITH CYHEXATIN
                                                                                                                               

    Laboratory                IDRC9                Dow USA             Hazleton, France        Hazleton, France
                                                                                                                               

    Test material
        purity                95.6%                94.8-95.5%          96%                     96%
        source                Dow                  Dow                 Oxon                    Oxon
        form                  powder               powder              powder                  powder

    Dose suspension
        vehicle               0.5% Methocel        0.5% Methocel       0.5% CMC                0.5% CMC
        volume                1 ml/kg bw           1 ml/kg bw          5 ml/kg bw              5 ml/kg bw
        preparation           once                 once                weekly                  weekly
        agitation             during dosing        continuous          during dosing           during dosing
        doses (mg/kg bw)      0, 0-5, 1.0, 3.0     0, 0.75, 3.0        0, 3.0, 3.0 (pure)      0. 0.5, 0.75, 1.0

    Experimental animals
        strain                NZWb, SPFc           NZW                 Hy/Cr NZ                Hy/Cr NZ
        source                Hazleton, Pa, USA    Hazleton, Pa, USA   Charles River, France   Charles River, France
        age                   about 5 months       not given           16-18 weeks             16-18 weeks
        weight (kg)           3.62 - 4.32          3.5 - 4.5           3.10 - 4.35             3.05 - 4.25
        insemination          artificial           artificial          matedd                  matedd
        acclimation           14 days              3 weeks             none                    none
        diet                  Purina #5322         Purina #5322        UARe                    UAR-112
        feeding               ad libitum           8 oz/day            200 g/day               200 g/day
        cage                  wire                 not given           plastic                 plastic
        housing               individual           individual          individual
                                                                                                                               

    a CMC = carboxymethyl cellulose
    b NZW = New Zealand white
    c SPF = Specific pathogen free
    d mated by supplier, delivered Day 1-2 of gestation
    e UAR = Usine d'Alimentation Rationnelle
    f rabbits received 4oz food/day prior to start of study (insemination)
    g IRDC = International Research and Development Corporation, Michigan, USA.
    

    REFERENCES

    Aldridge, D., Schwartz C.A., Keller, K.A. & Schardein, J.L. (1986) 
    Cyhexatin -Oral teratology study in Sprague-Dawley rats (with
    appendix tables).  Unpublished Report No. 133-048 from International
    Research and Development Corporation (IDRC).  Submitted to WHO by
    Dow Chemical Co., Midland, Michigan, USA.

    Berdasco, N.M., Johnson, K.A., Wolfe, E.L. & Hanley, T.R. Jr (1986) 
    Cyhexatin: oral teratology probe study in New Zealand White rabbits 
    Unpublished Report from Mammalian and Environmental Toxicology
    Research Laboratory, Dow Chemical Co., Midland, Michigan.  Submitted
    to WHO by Dow Chemical Co., Midland, Michigan, USA.

    Kirk, H.D., Johnson, K.A. & Hanley, T.R., Jr (1987a)  Oral
    teratology study in New Zealand White rabbits  Unpublished Report
    from Mammalian and Environmental Toxicology Research Laboratory, Dow
    Chemical Co., Midland, Michigan.  Submitted to WHO by Dow Chemical
    Co., Midland, Michigan, USA.

    Kirk, H.D., Johnson, K.A. & Hanley, T.R., Jr (1987b)  Dermal
    teratology study in New Zealand White rabbits.  Unpublished Report
    from Mammalian and Environmental Toxicology Research Laboratory, Dow
    Chemical Co., Midland, Michigan.  Submitted to WHO by Dow Chemical
    Co., Midland, Michigan, USA.

    Monnot, G. (1989a)  Cyhexatin - oral (gavage) teratology study in
    the rabbit.  Unpublished study number 827/001 from Hazleton, France. 
    Submitted to WHO by Oxon Italia S.p.A., Milan, Italy.

    Monnot, G. (1989b)  Cyhexatin - teratology study by oral route in
    the rabbit.  Unpublished study number 827/001+005 from Hazleton,
    France.  Submitted to WHO by Oxon Italia S.p.A., Milan, Italy.

    Monnot, G. (1989c)  Teratology study by percutaneous route in the
    rabbit.  Unpublished study number 827/006 from Hazleton, France. 
    Submitted to WHO by Oxon Italia S.p.A., Milan, Italy.

    Monnot, G., Roffino, D. & Gonnet, J.F. (1989a)  Cyhexatin.  General
    tolerance and tissue concentration after 13 administrations by the
    oral route in the rabbit.  Unpublished Report No. 222088-D, study
    number 827/007 from Hazleton, France.  Submitted to WHO by Oxon
    Italia S.p.A., Milan, Italy.

    Monnot, G., Roffino, D. & Gonnet, J.F. (1989b)  Cyhexatin. 
    Evaluation of the local tolerance and tissue concentration after 13
    administrations by the percutaenous route in the rabbit. 
    Unpublished Report No. 806970-D, study number 827/004 from Hazleton,
    France.  Submitted to WHO by Oxon Italia S.p.A., Milan, Italy.

    Schardein, J.L., Miller, L., Schwartz, C.A. & Keller, K.A. (1986) 
    Tricyclohexyltin hydroxide:  teratology study in rabbits. 
    Unpublished Report from International Research and Development Corp.
    (IDRC).  Submitted to WHO by Dow Chemical Co., Midland, Michigan,
    USA.


    See Also:
       Toxicological Abbreviations
       Cyhexatin (WHO Pesticide Residues Series 4)
       Cyhexatin (WHO Pesticide Residues Series 5)
       Cyhexatin (Pesticide residues in food: 1978 evaluations)
       Cyhexatin (Pesticide residues in food: 1980 evaluations)
       Cyhexatin (Pesticide residues in food: 1981 evaluations)
       Cyhexatin (Pesticide residues in food: 1983 evaluations)
       Cyhexatin (Pesticide residues in food: 1991 evaluations Part II Toxicology)
       Cyhexatin (JMPR Evaluations 2005 Part II Toxicological)