Candoxatril, a prodrug for candoxatrilat, a selective inhibitor of neutral endopeptidase, was administered orally to groups of 24 female rats at doses of 0, 120, 400 or 1200 mg/kg/day from gestation day 6 to lactation day 21 to assess effects in pre- and postnatal development of F₁ offspring. All dams were allowed to litter and to raise their F₁ offspring until lactation day 21. The F₁ offspring were examined for postnatal developmental indices, reflex behaviors and memory. A functional observational battery(FOB)was also conducted. A marked increase in spontaneous activity of the dams was observed in all condoxatril-treated groups. Maternal body weight gain was decreased in the 400 and 1200 mg/kg/day groups during the treatment periods. No significant differences were found for reproductive parameters. The male and female pups in the 1200 mg/kg/day group had significantly lower body weights beginning on postnatal days 21 and 14, respectively, through to the end of the study. There were no drug-related effects on pre- and postnatal developmental indices, FOB, sensory function tests or memory test. The no observed adverse effect levels were 120 and 400 mg/kg/day for the F₀ dams and F₁ offspring, respectively.

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A repeated oral dose toxicity study of methotrexate(MTX)was conducted in order to examine whether the enhancement of MTX toxicity would occur in unilaterally nephrectomized(UNX)rats. UNX rats or sham-treated(SHAM)rats received dosages of 0, 0.06, 0.2 or 0.6 mg/kg/day(control animals received physiological saline). Toxic effects of MTX observed in this study were not different from studies already conducted, i.e., myelo- and lympho-toxicity, gastrointestinal toxicity, hepatotoxicity, pulmonary toxicity and renal toxicity were evident in the animals given MTX. Toxic effects of MTX in the UNX rats were more severe than those in the SHAM rats;a higher number of dead and moribund animals was observed among the UNX rats, and abnormal clinical signs appeared a few days earlier in the UNX rats. In the hematological examination, a decreased number of the blood cells in the UNX rats was observed at the lower dose level as compared to SHAM rats. The nontoxic dose of MTX in SHAM rats and UNX rats was 0.06mg/kg/day and below 0.06mg/kg/day, respectively. According to the results of a toxicokinetic examination conducted in the animals receiving 0.2mg/kg/day, AUC and T_1/2terminal of MTX in the UNX rats were higher than those of SHAM rats. It was considered that the enhancement of the MTX toxicity in UNX rats was caused by the longer exposure of MTX in UNX rats. Serum UN and Cr of the UNX rats receiving physiological saline were higher than those of the corresponding SHAM rats, which suggested a slightly decreased GFR had been induced in UNX rats in this study. However, decreased PSP excretion was not observed in the UNX rats and urine volume of the UNX rats was equivalent to that of SHAM rats. Thus, it was considered that vicarious hypertrophy occurred in the residual kidney and decreased renal function was not evident in the UNX rats. This study demonstrated that the enhancement of toxicity of MTX had occurred even though a decreased renal function was not evident.

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NK-104, an inhibitor of 3-hydroxy-3-methylglutaryl-CoA reductase, was administered orally to Wistar rats at a dose of 2, 10, 50 or 100 mg/kg for 28 days consecutively, and the toxicity of NK-104 and its recovery with 2 weeks cessation of drug treatment were examined. As major clinical signs, loose stool, diarrhea, crouching and emaciation were observed in both sexes at 50 or 100 mg/kg, and all females at 100 mg/kg died or became moribund due to severe emaciation before the completion of treatment. The suppression of body weight gain or decrease in body weight was observed in the female dose group at 50 mg/kg and both sexes at 100 mg/kg. Decreased food intake was observed in both sexes at 100 mg/kg. Moreover, an increase in cholinesterase(Ch.E)in the male dose groups at 50 and 100 mg/kg and an increase in glutamic oxaloacetic transaminase(GOT)and glutamic pyruvic transaminase(GPT)in the female dose group at 50 mg/kg were observed in blood chemistry testing. Macroscopic examination showed thickening of the forestomach mucosa in the groups of 10 mg/kg or more. Microscopic examination revealed hyperkeratosis and hypertrophy of the spinous layer associated with both cell infiltration of the mucosal propria and submucosal edema. In addition, skeletal muscle lesions including atrophy, vacuolation and focal necrosis were observed in the female dose groups at 50 and 100 mg/kg. The above-mentioned microscopic changes were not observed on cessation of drug treatment. The non-toxic dose level of NK-104 in the 28-day repeated oral toxicity study using rats was determined to be 2 mg/kg.

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NK-104 is a novel potent inhibitor of the rate-limiting enzyme in cholesterol biosynthesis, 3-hydroxy-3-methylglutaryl coenzyme A(HMG-CoA)reductase, and has been shown to be a highly effective agent in lowering blood cholesterol. In the present study, NK-104 was orally administered to Wistar rats at a dose of 0.3, 1, 3 or 10 mg/kg for 6 months for examination of toxicity. Additional recovery groups of 8 rats each of both sexes receiving 0 and 10 mg/kg were maintained without treatment for 1 month in order to assess recovery. As a result, no toxicological changes were observed in general signs, body weight, food intake, ophthalmological examination, urinalysis, hematological and blood chemical examinations or organ weights. An autopsy revealed thickening of the forestomach mucosa in both sexes at a dose of 1 mg/kg or more. This change was microscopically recognized as hyperkeratosis and hypertrophy of the spinous layer associated with both cell infiltration of the mucosal propria and edema of submucosa in the forestomach in both sexes at doses of 3 and 10 mg/kg. Forestomach changes were not observed in any cases after 1 month cessation of drug treatment. The non-toxic dose of NK-104 in the 6-month repeated oral toxicity study in rats is estimated to be 1 mg/kg/day.

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