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 Since the evaluation in 1985, cyhexatin has been withdrawn from use as an acaricide in a number of countries as a result of new teratology studies.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)