FLUBENDAZOLE First draft prepared by Dr Radovan Fuchs Institute for Medical Research and Occupational Health University of Zagreb, Croatia 1. EXPLANATION Flubendazole([5-(4-fluorobenzoyl)-1H-benzimidazole-2-y1]-carbamic acid methyl ester) belongs to the group of benzimidazole carbamates. Flubendazole is an anthelminthic agent active against a range of gastrointestinal parasites in pigs and poultry. Flubendazole had not been previously evaluated by the Joint FAO/WHO Expert Committee on Food Additives. 2. BIOLOGICAL DATA 2.1 Biochemical aspects 2.1.1 Absorption, distribution and excretion Groups of 18 Wistar rats and 12 multi-mammate rats (Mastomys natalensis) were given an oral dose of 40 mg/kg bw of flubendazole as a microsuspension. The same amount of test substance was given subcutaneously to 24 Wistar rats and 12 multimammate rats. Groups of six rats of both strains were sacrificed by decapitation at 4 and 8 h and at 24 and 48 h after administration to Wistar rats. Plasma levels of flubendazole after oral administration were found to be 81 and 17 ng/ml at 4 h in the Wistar rats and multimammate rats, respectively. The estimated half-life was 6-7 h. At 24 h the flubendazole plasma level in the Wistar rats was 5.6 ng/ml. Plasma concentrations after subcutaneous injection was very low. Peak plasma levels of 7-9 ng/ml were observed after 4-8 h in both strains. After 48 h, plasma levels represented 32% of the peak level, indicating very slow absorption of the drug from the injection site (Michiels et al., 1980a). Groups of male Wistar rats were given oral doses of 10 mg/kg bw microcrystalline suspension of 14C-labelled flubendazole. Animals were sacrificed at different intervals (0.5, 1, 2, 4, 6, 16 and 24 h after administration). Peak plasma levels of unchanged flubendazole were observed after 0.5 h and the drug was eliminated with a half-life of 6 h. Generally, the concentration of flubendazole in blood and plasma was very low, and was almost unchanged at 0.5 h (0.27 µg/ml) and 24 h (0.18 µg/ml) after exposure. After 24 h, nearly 50% of the dose was excreted via faeces while 4% of the dose was excreted in urine as metabolites. The amount of total radioactivity present in the liver, lung, kidney, muscle and fat was very low and did not exceed 3.1 µg/g of tissue (Michiels et al., 1977a). Five male Wistar rats were each given an oral dose of 10 mg/kg bw of 14C-labelled flubendazole. Within 4 days, 7% of the dose was excreted in urine, and 89% in faeces. After 48 h, 91% of administered flubendazole was excreted. Radioactivity in urine was due to metabolites while in faeces the radioactivity was mainly due to the unchanged drug. The main metabolites identified in urine were present mainly in the form of glucuronides and resulted from carbamate hydrolysis and reduction of ketone (Meuldermans et al., 1977). 14C-Labelled flubendazole was given orally to 3 female beagle dogs at a dose of 10 mg/kg bw. A total of 88% of the radioactivity was excreted within 4 days after administration. The majority of the radioactivity (81.5%) was measured in faeces, while only 6.3% was found in urine. Radioactivity found in urine was related to metabolites of flubendazole. In samples of faeces collected during 48 h, the radioactivity was almost exclusively due to unchanged flubendazone. There are indications that flubendazole may undergo enterohepatic circulation (Meuldermans et al., 1978). A group of 2 male and 4 female beagle dogs was treated orally with flubendazole at a dose of 22 mg/kg bw. Plasma levels peaked at 2 to 8 h after dosing (4-5 ng/ml) (Michiels et al., 1987). Eight male beagle dogs were divided into groups of two and were given micro-suspensions of flubendazole intramuscularly. Doses of 2.5 and 25 mg/kg bw were given as single injections or as repeated injections for five consecutive days. Blood tests were made during 42 days after administration. At both doses, three phases in plasma concentration-time curves were observed. First there was a fast phase, with more rapid release of the drug from the injection site than its elimination from the body. A second phase showed faster elimination than release from the depot and a third phase showed very slow terminal resorption. After a single injection of 2.5 mg/kg bw, peak plasma levels appeared after 3-5 days at concentrations up to 0.6 ng/ml. With a single injection of 25 mg/kg bw, maximal plasma levels up to 2.1 ng/ml were observed 5-7 days after administration. Repeated injections for 5 consecutive days gave maximal plasma levels at 3-4 days after the last dose; concentrations found were 2.4 and 13.2 ng/ml for the low and high dose, respectively. The elimination half-life for both doses and regimes was estimated to be 24 h (Michiels et al., 1980b). Pigs were given 14C-flubendazole, labelled in the 2-position of the benzimidazole ring at a dose of 1.5 mg/kg bw for five consecutive days. A total of 79% of the administered dose was excreted within 30 days after the medication period (23% in urine and 56% in faeces). The main metabolic pathways were carbamate hydrolysis and ketone reduction (Meuldermans et al., 1982). 2.1.2 Biotransformation Reduction of the ketone functional group and hydrolysis of the carbamate moiety are the main biotransformation pathways of flubendazole. To some extent, methylation has also been found as a relatively minor pathway. In rats and dogs, the urinary metabolites are formed exclusively by ketone reduction, carbamate hydrolysis and glucuronide and sulfate conjugation (Meuldermans et al., 1977, 1978). The metabolic pathways of flubendazole in different animal species, adapted from Van Leemput, et al., 1991, is presented in Figure 1.2.2 Toxicological studies 2.2.1 Acute toxicity studies The acute toxicity of flubendazole is summarized in Table 1. In some cases the animals exhibited exophthalmus, hypotonia, slight sedation, general depression, ataxia, convulsions and pilo-erection. Deaths were recorded within the first 24 h after intraperitoneal administration of test substance. Table 1. Acute toxicity of flubendazole Species Sex Route LD50 Reference (mg/kg bw) Mouse M&F oral* >5000 Niemegeers, 1974 M&F oral# >10 000 Nakaoka et al., 1983a M&F s.c.* >5000 Niemegeers, 1986a M&F s.c.# >10 000 Nakaoka et al., 1983a M i.p.# 528 Nakaoka et al., 1983a F i.p.# 434 Nakaoka et al., 1983a Rat M&F oral* >5000 Niemegeers, 1974 M&F oral# >10 000 Nakaoka et al., 1983b M i.p.# 435 Nakaoka et al., 1983b F i.p.# 252 Nakaoka et al., 1983b M&F s.c.# >5000 Nakaoka et al., 1983b M&F s.c.* >10 000 Niemegeers, 1986b Guinea-pig M&F oral* >5000 Niemegeers, 1974 M s.c.* 4679 Niemegeers, 1986c F s.c.* 4834 Niemegeers, 1986c Laying-hen F oral >640 Vanparijs & Desplenter, 1982 Guinea fowl oral >1200 Le Brun, 1983 * vehicle: aqueous suspension with 1% polysorbate 80 # vehicle: 0.5% methylcellulose solution 2.2.2 Short-term toxicity studies 2.2.2.1 Rats In a 3-month study flubendazole admixed with the diet at levels of 0, 10, 40 or 160 mg/100 g food was given to Wistar rats (10 rats/sex/dose level). The approximate intakes of flubendazole over the period of the study were equal to 0, 8, 30 or 130 mg/kg bw/day for males and 0, 9, 40 or 150 mg/kg bw/day for females. No treatment-related effects were observed on mortality, behaviour, appearance, food consumption, body weight, haematology, serum analysis, urinalysis, microscopy, organ weight or histopathology (Marsboom, 1975a). 2.2.2.2 Dogs Groups of beagle dogs (3 dogs/sex/group) were given flubendazole orally as a powder in gelatin capsules at doses of 0, 2.5, 10 or 40 mg/kg bw/day, six days per week, over 3 months. Control animals received 250 mg lactose only. Observations included behavioural changes, food consumption, body weight, ECG, blood pressure, haematology, serum analysis, urinalysis, necropsy, organ weight and histopathology. Small-sized prostate and congestion of cauda of the epididymis were observed in all males at doses of 10 and 40 mg/kg bw/day. Histopathologically some atrophic changes of the prostate were noticed at the higher dose groups, but the changes were not dose-related. Atresic changes in the ovaries were noted in 2 females in the 2.5 mg/kg bw/day group, 1 in the 10 mg/kg bw/day group and 3 in the 40 mg/kg bw/day group. Atrophic changes of the uterine wall and vagina in some dosed females were also observed. According to historical control data the changes in the female genital tract were considered to be within the normal range for the age of the dogs (Marsboom et al., 1975). Subsequent to the above report the histopathological slides were evaluated by two independent pathologists. Both experts agreed that the atrophic changes were not indicative of a treatment-related toxic effect and should be considered as incomplete development in sexually immature dogs (Thoonen, 1987; Powell, 1991). Because of the lack of conclusive evidence as to the etiology of these changes, the Committee concluded that the NOEL in this study was 2.5 mg/kg bw/day. 2.2.2.3 Chickens Flubendazole was given to 4 groups of broiler breeder pullets (50 F + 5 M/group) over a period of 7 days. The drug was admixed in the feed at concentrations of 0, 60, 120 or 180 mg/kg. Four days after the end of treatment 10 hens and a cock were removed from the groups for blood sampling and necropsy. The only significant difference in haematological parameters was a lower haematocrit value and red blood cell count in the highest-dose group. Clinical biochemistry tests showed significant increases in triglycerides and phospholypides at 120 mg/kg, decreased aspartic aminotransaminase at 180 mg/kg and decreased cholinesterase at 120 and 180 mg/kg. Histopathologically, treatment-related effects were observed in the spleen of the high-dose group, in reduction of the white pulp area and reduction of the number of red blood cells in the red pulp. The NOEL in this study was 120 mg/kg, equivalent to 15 mg/kg bw/day (Desplenter & Coussement, 1985). 2.2.3 Long-term/carcinogenicity studies 2.2.3.1 Mice Four groups of 50 male and female Swiss albino mice were fed diets containing 0, 5, 10 or 20 mg/100 g flubendazole for a period of 18 months. The intake of the drug over the study period was equivalent to 7.5, 15 or 30 mg/kg bw/day (data on food consumption and body weight were not provided). The mortality rate, clinical observations and presence of subcutaneous masses were recorded daily. A complete necropsy and histopathological examination were performed at termination of the study. No treatment-related effects were noted for clinical condition or survival. The percent survival for treated groups was comparable to the controls, as shown in Table 2. Table 2. Survival at 18 months in the long-term study in mice Sex Dose mg/kg bw/day 0 7.5 15 30 M 54% 44% 38% 38% F 40% 34% 40% 32% The total number of benign and malignant tumours was similar for treated and control groups. The most common types of tumours were hepato-cellular tumours and alveologenic lung carcinoma. No effect of flubendazole was evident histopathologically. The NOEL in this study was 30 mg/kg bw/day (Verstraeten, et al., 1983a). 2.2.3.2 Rats Groups of 50 Wistar rats of each sex were fed diets containing 0, 10, 20 or 40 mg/100 g flubandezole for 24 months. Drug intake was equivalent to 5, 10, or 20 mg/kg bw/day. All animals were observed once daily for signs of abnormal behaviour and clinical effects. At termination of the study a full necropsy was performed and the organs were examined histopathologically. The mortality rate was very high in all groups of animals including the controls at the end of the study. There was no statistically-significant difference in mortality rates between the groups during the entire period of the study. There were no treatment-related effects among the treated and control animals. During the study subcutaneous masses in females were noted in approximately 20% of the control and 40% of the high-dose animals. On necropsy a significantly increased incidence of pale kidneys was observed in females at 5 and 20 mg/kg bw/day. However, there was no histopathological evidence for dose-related changes in the kidney. Flubendazole at concentrations of up to 40 mg/100 g feed for 2 years did not show biological or statistical evidence of incidence of neo-plasms. The NOEL in this study was 20 mg/kg bw/day (Verstraeten et al., 1983b). 2.2.4 Reproduction studies 2.2.4.1 Mice Groups of 30 female Swiss albino mice were given flubendazole in a single dose of 0, 20, 80 or 320 mg/kg bw. The drug was administered orally by gavage in microsuspension vehicle. A control group of females received vehicle suspension only. All the females were mated with untreated males. The animals were controlled daily over a period of 360 days. During the experiment the mortality rate, incidence of pregnancy, time interval between dosing and birth, and number of pups were not affected by treatment. By comparing the data from control and treated animals, no differences were noted regarding mortality of females, the average time interval between dosing and birth of first litters or litter size per female. In the high-dose group (320 mg/kg bw) a reduction of mean number of pups per female was observed. The NOEL in this study was 80 mg/kg bw (Marsboom, 1977a). 2.2.4.2 Rats In a fertility study, Wistar rats (20 animals/sex/dose) were given flubendazole admixed in feed. The concentration of the test substance in the diet was 0, 2.5, 10 or 40 mg/100 g, equivalent to 2.5, 10 or 40 mg/kg bw/day. Females were treated with flubendazole for 14 days prior to cohabitation with males and during the pregnancy period. Males received flubendazole over a period of 60 days before mating. Untreated animals were mated with treated ones. No drug effects were noted regarding food consumption or average weight gain of females. All the females were sacrificed on the 22nd day post-mating. No drug effects were noted on incidence of pregnancy and the percentage of pregnancies was 100% in almost all groups. In all females the average number of implantations and percentages of live, dead and resorbed fetuses were similar and not affected by the treatment. Treatment-related fetal skeletal abnormalities were not observed. The NOEL in this study was 40 mg/kg bw/day (Marsboom, 1976a). Four groups of 20 Wistar rats were given flubendazole admixed in feed at concentrations of 0, 2.5, 10 or 40 mg/100 g feed, equivalent to 0, 2.5, 10 or 40 mg/kg bw/day from day 16 of gestation up to the 3-week-lactation period. The average body weight and food consumption were not significantly different among the groups. Only one female from the 40 mg/kg bw/day group died during the time of treatment. The pregnancy rate, average duration of gestation and fetal parameters were comparable among the treated and control groups. No abnormalities were found among offspring in any of the groups in the study. The NOEL in this study was 40 mg/kg bw/day (Marsboom, 1976b). 2.2.4.3 Pigs A study was performed on 5 different pig farms. On each farm 16 sows and 1 boar received flubendazole admixed in the feed, providing a dose of 3 mg/kg bw/day. On each farm the same number of non-treated animals served as controls. Each boar was mated with 8 treated and 8 control sows. The treated sows received flubendazole diet from estrus till parturition, while boars were treated two months prior to the first mating and until all sows were successfully bred. During the study no differences were observed on conception rate of the boars, estrus behaviour or gestation length. Post-partum conditions were normal except in 7 sows, which were found to be related to dystocia. The number of live and dead piglets among the different groups was not statistically different. There were no significant differences in abnormalities observed among the piglets from any groups except in slightly increased number of mummifications. The investigators associated mummifications to the endemic occurrence of pseudorabies and parvovirus infections in the area where the study was performed. The time interval betwen weaning to the next estrus were equal among the groups (De Keyser et al., 1984) 2.2.5 Special studies on embryotoxicity/teratogenicity 2.2.5.1 Rats Groups of 20 young female Wistar rats were fed diet containing flubendazole at concentrations of 0, 2.5, 10 or 40 mg/100 g feed, equivalent to 0, 2.5, 10 or 40 mg/kg bw/day, from day 6 to day 15 of pregnancy. Parameters measuring body weight, food consumption, mortality and pregnancy were recorded. The animals were sacrificed on the 22nd day of pregnancy and the fetuses were delivered by caesarean section. The number of live, dead and resorbed fetuses was recorded, average body weight of pups was measured and the fetuses examined for abnormalities. During the study none of the animals died and food consumption and average body weight were comparable among the groups. The percentage of pregnancies in all treated groups was 95% and in the control group 90%. All the fetal parameters studied were comparable among the treated and control groups. The absence of metacarpal and metatarsal bones was noticed in only one fetus from the highest dose group. The NOEL in this study was 40 mg/kg bw/day (Marsboom, 1974). In a separate study, four groups of 20 female Wistar rats each were treated with flubendazole in the diet at concentrations of 0, 2.5, 10 or 40 mg/100 g feed, equivalent to 0, 2.5, 10 or 40 mg/kg bw/day. The study design and parameters studied were the same as described in the previous study. There were no changes in any of the parameters studied. The NOEL was 40 mg/kg bw/day (Marsboom, 1975b). A third study (same experimental design) was carried out in order to confirm the results of the previous studies. The test substance in this experiment was given orally by gavage at doses of 0, 2.5, 10 or 40 mg/kg bw/day. All the maternal and fetal parameters were comparable among the treated and control groups of animals. The NOEL in this study was 40 mg/kg bw/day (Marsboom, 1977b). Groups of female Wistar rats (20 animals/group) were given flubendazole admixed in a powdered diet at concentrations of 0, 10, 40 or 160 mg/100 g feed, equivalent to 0, 10, 40 or 160 mg/kg bw/day from days 6 to 15 of pregnancy. The same parameters as in the previous experiments were studied. Food consumption and average body weight were comparable among all groups. During the study no mortalities occurred. The percentage of pregnancies was high and comparable among the groups. No evidence of embryotoxicity or teratogenicity was found. The NOEL in this study was 160 mg/kg bw/day (Marsboom, 1978). Flubendazole extracted from commercially formulated drug was suspended in water and given by gavage to female Sprague-Dawley rats (20 animals/group) at doses of 0, 2.5, 10, 40 or 160 mg/kg bw/day from day 8 to day 15 of pregnancy. On day 21 of pregnancy the animals were sacrificed and the number of implantation sites and live fetuses were recorded. The fetuses were further examined for malformations. During the study period signs of maternal toxicity were not observed. The highest dose (160 mg/kg bw/day) was found to be embryocidal, resulting in a significant increase in the fetal resorption rate. A dose-dependent decrease in fetal body weight occurred, which was significant at 40 and 160 mg/kg bw/day. The two highest doses induced significant gross, skeletal and internal malformations. In the 160 mg/kg bw/day dose group, 16.8% of fetuses were grossly malformed. The malformations were described as: encephalocele, cranial meningocele, omphalocele, ectrodactyly, club foot, anal atresia, spina bifida occulata and tail defects. Skeletal malformations affected mainly the vertebrae and ribs, and significant malformations were found in 24.6% and 32.6% of fetuses in the two highest dose groups. Significant internal malformations were observed in 19.8% and 47.7% of fetuses in the 40 and 160 mg/kg bw/day group. respectively. The NOEL in this study was 10 mg/kg bw/day (Yoshimura, 1987). 2.2.5.2 Rabbits Groups of 20 female New Zeeland white rabbits were orally administered 0, 10 or 40 mg flubendazole/kg bw/day from day 6 to day 18 of gestation. The females were sacrificed on gestation day 28 and fetuses were delivered by caesarean section. The animals from all doses were necropsied. The fetuses were weighed and examined for external anomalies. After incubation of the pups the survival rate was calculated. All the fetuses were radiographically examined. One-third of the fetuses were examined for visceral anomalies and the rest were preserved and used for additional analysis. During the study one non-pregnant female in the highest dose group died due to infection. The average body weight increase was comparable among all groups. No differences were observed in pregnancy rate among the groups and no teratogenic effects were found among the offspring. The percentage of live, dead and resorbed fetuses and survival rate of incubated pups from all groups were not significantly different. The NOEL in this study was 40 mg/kg bw/day (Marsboom, 1976c). 2.2.5.3 Pigs Flubendazole (5% powder formulation) was admixed in the diet at a concentration of 30 mg/kg and given to 6 crossed Landrace-Pietrain sows from day 8 to day 50 of pregnancy. Altogether 62 piglets were born. No piglets were stillborn and no abnormalities were recorded (Marsboom, 1976d). In a separate study flubendazole (5% powder formulation) admixed in the feed at a concentration of 200 mg/kg, equivalent to 8 mg/kg bw/day, was given to 20 sows from the first day of mating until the day of farrowing. Three sows were withdrawn from the experiment after 3 weeks. In the group of 17 sows having successful pregnancies 154 live and 8 stillborn piglets were recorded. There were no detectable external abnormalities, except for a mild form of sprayed legs observed in 2 piglets of one sow. Abnormalities were not found in stillborn piglets (Rogiers, 1979). A group of 8 sows was given 50 mg flubendazole/kg bw/day admixed in the diet from the first day of mating until day 70 of pregnancy. Sixty-three piglets of normal weight and 3 stillborn piglets were born. No external abnormalities were recorded (Rogiers, 1980). 2.2.6 Special studies on eye and skin irritation 2.2.6.1 Rabbits A group of 6 adult New Zeeland rabbits had 0.1 ml of a 50% w/w suspension of a 5% premix formulation instilled into the conjunctival sac of the left eye. There were no signs of eye irritation during the observation time of 21 days (Teuns & Marsboom, 1987a). A flubendazole formulation was applied to intact skin of New Zeeland rabbits. The test sites were occluded for 24 h. After removal of dressings, the test sites were scored for erythema and oedema. A barely perceptible irritation (index 0.63) was noted during the first 5 days in the treated animals according to the Draize irritation index. This irritation was fully reversible after 5 days. This study was designed primarily to determine the dermal LD50 value (Teuns & Marsboom, 1987b). 2.2.7 Special studies on genotoxicity The genototoxicity of flubendazole is summarized in Table 3. Table 3. Results of genotoxicity studies on flubendazole Test system Test object Concentration Results Reference In vitro Repair test B. subtilis 1-5000 µg/disc Negative Yamashita & Hattori, 1983 Ames test +/- S9 S. typhimurium 10-5000 µg/plate Negative Yamashita & TA1535, TA1537, Hattori, 1983 TA1538, TA100, TA98 E. coli N/r WP2 trp hcr S. typhimurium 0.5-1000 µg/plate Negative Jagannath & TA535, TA1537, Brusick, 1978 TA1538, TA98, TA100 S. cerevisiae D4 In vivo Sex-linked Drosophila 500 and 2000 ppm Negative Vanparys & melanogaster feeding/3d Marsboom, 1982 Micronucleus Male Swiss albino 2 oral doses: 40, Negative Vanparys & test mice 80, 160, Marsboom, 1979 1280 mg/kg bw female Wistar 2 oral doses: 80, Negative Vanparys & rats 160, 640 mg/kg bw Marsboom, 1981 Dominant Male Swiss albino single oral dose: Negative Marsboom, 1977c lethal mice 10, 40, 160 mg/kg bw 2.3 Observations in humans Three male volunteers were given single doses of flubendazole orally in 100 mg tablets. Flubendazole was mainly excreted in faeces (77.3% of the administered dose) within 3 days after intake of the drug. Less than 0.1% of the dose was excreted in the urine as unchanged drug (Heykants et al., 1975). Three male volunteers were given oral doses of 100 mg flubendazole 2 h before meals, 2000 mg flubendazole immediately after a heavy meal and 2000 mg flubendazole before a meal. Serum concentrations of flubendazole were monitored. The plasma concentration was very low, and peak levels after 100 and 2000 mg doses taken before meals were 0.35 and 0.74 ng/ml, respectively. In the case of flubendazole taken after a heavy meal, the peak plasma concentration was markedly higher (4.06 ng/ml), which indicates that the presence of food enhances the absorption of flubendazole from the gastro-intestinal tract. By calculating the area under the curve (AUC) values it was found that the absorption of the drug was not dose-dependent. AUC values increased only 1.4-fold after a 20-fold increase in dose (Michiels et al., 1977b). 3. COMMENTS A substantial database was available for assessment, including data on kinetics and metabolism, acute toxicity, short-term and long-term toxicity, reproductive and developmental toxicity, and genotoxicity. The absorption, metabolism, and excretion of flubendazole have been studied using radiolabelled drug. Flubendazole is poorly absorbed and metabolized in a qualitatively similar way in all species studied. More than 50% of the ingested drug is eliminated unchanged in the faeces. The absorbed drug is rapidly metabolized, so that levels of parent drug in the blood and urine are extremely low. The main site of metabolism is the liver, and major metabolic pathways are carbamate hydrolysis and ketone reduction. It seems probable that flubendazole undergoes enterohepatic circulation. Single oral doses of flubendazole were slightly toxic to experimental animals, the median lethal dose (LD50) being greater than 5000 mg/kg of body weight in mice, rats, and guinea-pigs. Flubendazole was given orally in gelatin capsules to dogs at doses of 2.5, 10 or 40 mg/kg bw/day, 6 days a week for 3 months. Some atrophic changes and congestion of the epididymis were observed in the male genital tract at doses of 10 and 40 mg/kg bw/day, and in the female genital tract at all doses. The changes in the female genital tract were considered to be within normal limits for dogs of the age of those used in the study. On histological examination of male sex organs, changes in the testes could not be clearly associated with flubendazole treatment. The findings in male dogs may not be compound-related, but because of the lack of conclusive evidence as to the cause of these changes, the Committee concluded that the no-observed-effect level (NOEL) was 2.5 mg/kg bw/day. Carcinogenicity studies were performed in mice and rats at doses up to 30 and 20 mg/kg bw/day respectively; no treatment-related effects were observed. There was no treatment-related increase in any type of neoplasm. The Committee was of the opinion that flubendazole had no carcinogenic potential at the highest doses administered in these studies. The results from a range of in vitro and in vivo genotoxicity tests were all negative. The Committee considered data from reproduction, embryotoxicity, and teratogenicity studies. Studies in mice, rabbits, and pigs were negative. Flubendazole was extensively studied in segmented reproduction studies in rats, performed as required for human drug regulation purposes and accepted by the Committee in lieu of a multigeneration reproduction study. In several rat developmental studies, doses of up to 40 and 160 mg/kg bw/day, given on gestation days 6-15, did not produce any embryotoxic or teratogenic effects. In a rat teratogenicity study published in 1987, using material extracted from a commercial preparation, gross skeletal and internal fetal malformations were recorded at doses of 40 and 160 mg/kg bw/day. The NOEL in this study was 10 mg/kg bw/day. 4. EVALUATION An ADI of 0-12 µg/kg of body weight was established for flubendazole, based on the NOEL of 2.5 mg/kg bw/day in the 3-month study in dogs, and a safety factor of 200. This safety factor was used by the Committee to take account of the fact that the doses were administered only 6 days per week in this study, the precise consequences of which could not be assessed. The Committee noted that the ADI also provided a safety margin corresponding to a factor of about 1000 with respect to the NOEL of 10 mg/kg bw/day derived from the rat teratogenicity study. The Committee considered that further carcinogenicity studies would not be required, since the highest dose used in the negative studies that it had evaluated exceeded the ADI by a factor of approximately 2000. 5. REFERENCES DE KEYSER, H., DONY, J. & ROGIERS, M. (1984). Fertility study with flubendazole (R 17889) in pigs. Unpublished results No. V4988 from Janssen Pharmaceutica Veterinary Department. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. DESPLENTER, L. & COUSSEMENT, W. (1985). Safety evaluation of flubendazole in broiler breeder chickens at higher than normal use levels: haematological, biochemical and histopathological evaluation. Unpublished results No.V5738 from Veterinary Clinical Research and Department of Toxicology, Janssen Pharmaceutica. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. HEYKANTS, J., WYNANTS, J. & SCHEIJGROND, H. (1975). The absorption and excretion of flubendazole in man. Unpublished results No. N10250 from Department of Drug Metabolism, Department of Separation Techniques and Department of Clinical Pharmacology Janssen Pharmaceutica. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. JAGANNATH, D.R. & BRUSICK, D.J. (1978). Mutagenicity evaluation of flubendazole in the Ames Salmonella/microsome plate test. Unpublished results No. 20988 from Litton Bionetics, Inc., 5516 Nicholson Lane, Kensington, Maryland. Submitted to WHO by Janssen Pharmaceutica, B-2340 Beerse, Belgium. LE BRUN, J. (1983). Acute toxicity of flubendazole in guinea fowls. Unpublished results No. V4899 from Department of Toxicology and Pharmacology JMG/MC. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. MARSBOOM, R. (1974). Potential of oral R 17889 for embryotoxicity and teratogenic effects in rats. Unpublished results No. 556 from Department of Toxicology, Janssen Pharmaceutica N.V. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. MARSBOOM, R. (1975a). Oral toxicity study in Wistar rats (repeated dosage for 3 months). Unpublished results No. 567, Janssen Pharmaceutica, Research Laboratories 2340 Beerse, Belgium. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. MARSBOOM, R. (1975b). Potential of oral R17889 for embryotoxicity and teratogenic effects in rats. Unpublished results No. 572 from Department of Toxicology, Janssen Pharmaceutica N.V. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. MARSBOOM, R., HERIN, V., VANDESTEENE, R. & PARDOEL, L. (1975). Oral toxicity study in beagle dogs (repeated dosage for 3 months). Unpublished results No. 568, Janssen Pharmaceutica, Research Laboratories 2340 Beerse, Belgium. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. MARSBOOM, R. (1976a). Oral male and female fertility study in Wistar rats. Unpublished results No. 695 from Department of Toxicology, Janssen Pharmaceutica N.V. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. MARSBOOM, R. (1976b). Oral embryotoxicity and teratogenicity study in Wistar rats. Unpublished results No. 692 from Department of Toxicology, Janssen Pharmaceutica N.V. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. MARSBOOM, R. (1976c). Oral embryotoxicity and teratogenicity study in New Zealand white rabbits (segment II). Unpublished results No. 692 from Department of Toxicology, Janssen Pharmaceutica. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. MARSBOOM, R. (1976d). Potential of oral flubendazole (R 17889) for teratogenic effects in pigs. Unpublished results No. 692 from Department of Toxicology, Janssen Pharmaceutica. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. MARSBOOM, R. (1977a). Total reproductive capacity test in female mice. Unpublished results No. 773 from Department of Toxicology, Janssen Pharmaceutica. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. MARSBOOM, R. (1977b). Oral embryotoxicity and teratogenicity study in Wistar rats (Segment II). Unpublished results No. 755 from Department of Toxicology, Janssen Pharmaceutica. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. MARSBOOM, R. (1977c). Dominant lethal test in male mice (single oral dose). Unpublished results No. 688 from Janssen Pharmaceutica, Research Laboratories. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. MARSBOOM, R. (1978). Oral embryotoxicity and teratogenicity study in Wistar rats (Segment II). Unpublished results No. 820 from Department of Toxicology, Janssen Pharmaceutica Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. MEULDERMANS, W., HURKMANS, R., SWIJSEN, E. & HEYKANTS, J. (1977). A comparative study on the excretion and metabolism of flubendazole (R17889) and mebendazole (R17635) in the rat. Unpublished report No. V2940 from Department of Drug Metabolism, Janssen Pharmaceutica. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. MEULDERMANS, W., SWIJSEN, E., HENDRICKX, J., LAUWERS, W., BRACKE, J., LENAERTS, F., SNEYERS, R. & HEYKANTS, J. (1978). On the absorption, excretion and biotransformation of flubendazole in the dog. Unpublished report No. N15186 from Department of Drug Metabolism and Pharmacology and Analytical Department, Janssen Pharmaceutica. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. MEULDERMANS, W., LEE, I.Y., HENDRICKX, J., SWYSEN, E., LAUWERS, W., PORTER, D. & HEYKANTS, J. (1982). Metabolism of flubendazole in swine: Excretion pattern of [2-14C] flubendazole and its metabolites and depletion kinetics of drug residues in edible tissues. Preliminary report from Department of Drug Metabolism, Department of Analytical Research, Janssen Pharmaceutica, and Pitman-Moore, Inc., Washington Crossing, NJ., USA. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. MICHIELS, M., HEYKANTS, J. & HENDRICKX, J. (1977a). Distribution of flubendazole (R17889) and its metabolites in the Wistar rat. Unpublished report No. N12336 from Department of Drug Metabolism and Analytical Department, Janssen Pharmaceutica. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. MICHIELS, M., HENDRIKS, J. & HEYKANTS, J. (1977b). The pharmacokinetics of mebendazole and flubendazole in animal and man. Arch. Internat. Pharmacodinam. Therapie, 256: 180-191. MICHIELS, M., HEYKANTS, J., VAN DEN BOSSCHE, H. & VERHOEVEN, H. (1980a). A comparative study on the systemic absorption of oral and subcutaneous mebendazole, flubendazole and R34803 in two different rodents. Unpublished report No. N19702 from Department of Drug Metabolism and Department of Comparative Biochemistry, Janssen Pharmaceutic. Submitted to WHO by Jansen Research Products Information Service, Janssen Pharmaceutical, B-2340, Beerse, Belgium. MICHIELS, M., PRINSEN, P., HEYKANTS, J. & VAN DEN BOSSCHE, H. (1980b). Systemic absorption of intramuscular flubendazole in the dog. Unpublished report No. N20709 from Department of Drug Metabolism and Department of Comparative Biochemistry, Janssen Pharmaceutic. Submitted to WHO by Jansen Research Products Information Service, Janssen Pharmaceutical, B-2340, Beerse, Belgium. MICHIELS, M., MONBALIU, J., WOESTENBORGHS, R., HEYKANTS, J. & MAES, L. (1987). Absorption and plasma concentrations of flubendazole in the dog after single oral administration at the therapeutic dose level of 22 mg/kg as the commercial flubendazole paste (Fflubenol KH pasteR). Unpublished report No. V6282 from Department of Drug Metabolism and Pharmacology and Animal Health Department, Janssen Pharmaceutica. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. NAKAOKA, A., FURUKAWA, T. & FUKUHARA, K. (1983a). Acute toxicity study of flubendazole in mice. Unpublished report No. V5050 from Research Laboratories, Fujisawa Pharmaceutical Co., Ltd., Osaka, Japan. Submitted to WHO by Janssen Pharmaceutica, B-2340 Beerse, Belgium. NAKAOKA, A., FURUKAWA, T. & FUKUHARA, K. (1983b). Acute toxicity study of flubendazole in rats. Unpublished report No. V5049 from Research Laboratories, Fujisawa Pharmaceutical Co., Ltd., Osaka, Japan. Submitted to WHO by Janssen Pharmaceutica, B-2340 Beerse, Belgium. NIEMEGEERS, C.J.E. (1974) The acute oral toxicity of flubendazole in Wistar rats, albino mice and guinea-pigs. Unpublished results No. N9208 from Department of Pharmacology, Janssen Pharmaceutica. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. NIEMEGEERS, C.J.E. (1986a). The acute subcutaneous toxicity of R17889 in mice. Unpublished results No. N49012 from Department of Pharmacology, Janssen Pharmaceutica. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. NIEMEGEERS, C.J.E. (1986b) The acute subcutaneous toxicity of R17889 in rats. Unpublished results No. N49023 from Department of Pharmacology, Janssen Pharmaceutica. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. NIEMEGEERS, C.J.E. (1986c) The acute subcutaneous toxicity of R17889 in guinea-pigs. Unpublished results No. N49024 from Department of Pharmacology, Janssen Pharmaceutica. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. POWELL, C.J. (1991). Independent report on slides from the flubendazole study No. 568. Unpublished results from Department of Toxicology St. Bartholomew's Hospital Medical College, University of London. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. ROGIERS, M. (1979). Potential of oral flubendazole (R17889) for teratogenic effects in pigs at 200 ppm during the whole gestation period. Unpublished results No. V3251 from Janssen Pharmaceutica. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. ROGIERS, M. (1980). Potential of oral flubendazole (R17889) for teratogenic effects in pigs at 50 mg per kg of bodyweight, administered during the first 10 weeks of the gestation period. Unpublished results No. V3443 from Janssen Pharmaceutica. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. TEUNS, G. & MARSBOOM, R. (1987a). Primary eye irritation study in rabbits. Unpublished results No. 1834 from Department of Toxicology, Janssen Pharmaceutica N.V. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. TEUNS, G. & MARSBOOM, R. (1987b). Acute dermal toxicity study in New Zealand White rabbits (single dose). Unpublished results No. 1835 from Department of Toxicology, Janssen Pharmaceutica N.V. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. THOONEN, H. (1987). Independent report on slides from the flubendazole study No 568. Unpublished results from Department of Pathology, Faculty of Veterinary Medicine, State University Ghent, Belgium. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. VAN LEEMPUT, L., MAES, L., MEULDERMANS, W. & HAYKANTS, J. (1991). Pharmacokinetic profile of flubendazole: critical review of available data. Unpublished review report from Department of Drug Metabolism and Pharmacokinetics, and Department of Parasitology, Janssen Pharmaceutic. Submitted to WHO by Jansen Research Products Information Service, Janssen Pharmaceutical, B-2340, Beerse, Belgium. VANPARYS, Ph. & MARSBOOM, R. (1979). Micronucleus test in mice. Unpublished results No. 912 from Department of Toxicology, Janssen Pharmaceutica, Research Laboratories. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. VANPARYS, Ph. & MARSBOOM, R. (1981). Micronucleus test in rats. Unpublished results No. 1032 from Department of Toxicology, Janssen Pharmaceutica, Research Laboratories. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. VANPARYS, Ph. & MARSBOOM, R. (1982). Sex-linked recessive lethal test in Drosophila melanogaster. Unpublished results No. 1138 from Department of Toxicology, Janssen Pharmaceutica, Research Laboratories. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. VANPARIJS, O. & DESPLENTER, L. (1982). The acute toxicity of flubendazole in poultry. Unpublished results No. V4501 from Department of Parasitology and Animal Health Department, Janssen Pharmaceutica. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. VERSTRAETEN, A., VANDENBERGHE, J., VAN CAUTEREN, H. & MARSBOOM, R. (1983a). Oral carcinogenicity study in Albino Swiss mice. Unpublished results No. 685 from Department of Toxicology, Janssen Pharmaceutica N.V. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. VERSTRAETEN, A., VANDENBERGHE, J., VAN CAUTEREN, H. & MARSBOOM, R. (1983b). Carcinogenicity study in Wistar rats. Unpublished results No. 684 from Department of Toxicology, Janssen Pharmaceutica N.V. Submitted to WHO by Janssen Research Products Information Service, Janssen Pharmaceutica, B-2340 Beerse, Belgium. YAMASHITA, T. & HATTORI, K. (1983). Mutagenic evaluation of flubendazole in bacterial repair and reverse mutagenesis test. Unpublished results No. V5051 from Research Laboratories Fujisawa Pharmaceutical Co., Ltd., Osaka, Japan. Submitted to WHO by Janssen Pharmaceutica, B-2340 Beerse, Belgium. YOSHIMURA, H. (1987). Teratogenicity of flubendazole in rats. Toxicology, 43: 133-138.
See Also: Toxicological Abbreviations FLUBENDAZOLE (JECFA Evaluation)