© 1986 Oxford University Press
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Association between Adverse Maternal and Embryo-Fetal Effects in Norfloxacin-Treated and Food-Deprived Rabbits
Merck Institute for Therapeutic Research West Point, Pennsylvania 19486
Association between Adverse Maternal and Embryo-Fetal Effects in Norfloxacin-Treated and Food-Deprived Rabbits. CLARK, R.L., ROBERTSON, R.T., PETER, C.P., BLAND, J.A., NOLAN, T.E., OPPENHEIMER, L., AND BOKELMAN, D.L. (1986) Fundam. Appl Toxicol 7, 272–286. Norfloxacin is a new antibiotic which caused embryo-fetal toxicity in association with materno-toxicity when given orally to rabbits at 100 mg/kg/day. The intestinal flora of rabbits is unusually sensitive to many antibiotics and it was suspected that the maternotoxicity and embryo-fetal toxicity caused by oral norfloxacin were secondary to an effect on the intestinal flora. To test this idea, a teratologic study was conducted in which rabbits were dosed on Days 6 to 18 of gestation with norfloxacin given orally at 100 mg/kg/day or subcutaneously at 20 mg/kg/day. The oral treatment caused decreased food consumption (to less than 15 g/day in some animals), body weight loss, an increased resorption rate, and decreased fetal weight. Among the females in the orally dosed group, there was a significant correlation (p
0.005) between the effects on maternal body weight and the resorption rate. The subcutaneous treatment caused little intestinal exposure (biliary excretion=only 2-4% of dose) and no maternotoxicity or embryo-fetal toxicity, even though blood levels of drug were at least as high as those in the oral group. Since the maternotoxicity and embryo-fetal toxicity were specific to the oral route and not correlated with the level of systemic exposure, the maternotoxicity may have been secondary to an effect on the intestinal flora and the embryo-fetal toxicity may have been secondary to the maternotoxicity. The decreased food consumption observed in the oral group may have contributed to the embryo-fetal toxicity since, in a separate study, it was found that lowering the amount of food provided to rabbits on Days 6 to 18 of gestation from 150 g/day to 50 or 15 g/day also caused adverse maternal and fetal effects including, at 15 g/day, fetal malformations.