The Journal of pharmacology and experimental therapeutics
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J. Pharmacol. Exp. Ther. · Apr 1976
Methadone during pregnancy in the rat: dose level effects on maternal and perinatal mortality and growth in the offspring.
Four groups of pregnant rats were administered methadone hydrochloride orally on days 8 through 22 of gestation. Each group initially received 5 mg/kg for 4 days. One group was maintained at this level and the remaining groups were increased to maintenance doses of 10, 15 or 20 mg/kg increments at 4-day intervals. ⋯ Body weights of offspring of mothers in the 20 mg/kg group remained well above average through weaning. In a second experiment, blood levels of methadone were determined for both mothers and litters in the 5, 10 and 15 mg/kg groups, sacrificed 24 hours before expected parturition. Blood levels were dose-related and corresponded to those found in human subjects receiving daily maintenance doses of approximately 30, 60 and 100 mg, respectively.