Postnatal persistence of methadone following prenatal exposure in the rat.

Tritiated methadone (3HME) was administered daily by gastric intubation to gravid rats during the last week of gestation. Fostered neonates were sacrificed every 5 days from birth to 30 days of age and brains and livers removed. Tissue 3HME was extracted, isolated on a high pressure liquid chromatograph, and counted. Highest concentrations of 3HME were present on the day of birth; after 5 days, approximately 22% remained. However, small but significant concentrations of 3HME were detected in tissues through 30 days of age. These results are of interest in relation to persistent opiate withdrawal symptoms in rat and human neonates.