Amniotic fluid transfer of meperidine from maternal plasma in early pregnancy.

Concurrent samples of maternal plasma and amniotic fluid were collected from 40 subjects during the second trimester of pregnancy following a single intramuscular dose of meperidine (100 mg). Maternal meperidine plasma levels were highest in samples collected from 15 to 50 minutes after drug administration. Thereafter the level declined during the next 2 hours. Meperidine was not detected in amniotic fluid until 30 minutes after the intramuscular dose. We estimated that an apparent equilibrium was reached between plasma and amniotic fluid at 120 to 155 minutes after the drug was given to the mother. Normeperidine was not detected in either maternal plasma or amniotic fluid during the time course of this study.