Norfloxacin, a new orally active antibiotic, was investigated in cynomolgus monkeys for potential developmental toxicity. Fifty seven monkeys were administered a control vehicle or norfloxacin by nasogastric gavage during the major period of organogenesis on gestational days (GD) 21 through 50 at doses of 0, 50, 100, 150, or 200/300 mg/kg/day. There was no evidence of teratogenicity at any dose level. Maternotoxicity and a significant increase in embryolethality occurred following doses of 200/300 mg/kg/day. The maternotoxicity was not expected based on rangefinding studies in nonpregnant female monkeys, which showed no signs of toxicity in doses up to 500 mg/kg/day. Additional studies were conducted to determine if norfloxacin caused similar toxicity later in gestation. Forty‐six pregnant monkeys were dosed with a control vehicle or 200 mg/kg/day norfloxacin for one of three 10‐day periods on GD 36–45, 71–80, or 111–120. There were no maternotoxic, embryotoxic, or fetotoxic effecs observed. Plasma concentrations of norfloxacin in five cynomolgus monkeys following 50 and 200 mg/kg oral doses were not dose‐proportionate. However, at a given dose, administered in cross‐over fashion, plasma concentrations of norfloxacin were higher in nonpregnant females (± 20–40%) than during pregnancy when the same subject was compared. At the no‐observed‐effect dose for maternal and embryotoxicity (50 mg/kg), peak plasma concentrations of norfloxacin in pregnant cynomolgus monkeys are approximately threefold higher than those observed in human volunteers receiving norfloxacin at the maximum recommended therapeutic dose of 400 mg (5.7 mg/kg based on 70 kg body weight) twice per day.
ASJC Scopus subject areas
- Developmental Biology
- Health, Toxicology and Mutagenesis