Methadone disposition during the perinatal period in humans.

To determine clinical and analytical feasibility of studies of narcotic disposition in the perinatal period, an initial prospective study of methadone disposition in one female, in chronic methadone treatment for heroin addiction, throughout pregnancy and in her neonate have been carried out. Two additional methadone-maintained patients were studied to determine the levels of methadone in simultaneously obtained specimens of plasma and breast milk. A progressive lowering of plasma levels of methadone during late pregnancy was observed. Measurable amounts of methadone were found in amniotic fluid, but without evidence of significant accumulation in this fluid. The apparent excretory half-life of methadone in the neonate was 32.5 hr. Amounts of methadone in breast milk were very small; the ratio of milk to plasma concentrations ranged from 0.05 to 1.2 over multiple time points following a daily oral dose of methadone. The total amounts of methadone which could be delivered to a neonate during the first month of life in breast milk from a mother maintained on moderate doses of methadone (e.g., 50 mg) are very small (less than 60 micrograms/d).