Metabolites of meperidine in the fetal and maternal serum.

Although meperidine appears to be the safest obstetric analgesic agent, it has been associated with infant respiratory depression in certain situations. It would appear that the incidence of fetal depression related to meperidine is dependent on the time of injection prior to delivery, the quantity of drug administered, and the rate of maternal metabolism of the analgesic. Previous work showed that meperidine is metabolized in the maternal system by one of three patterns. The present study demonstrates that the particular maternal serum pattern is characteristic for the individual, regardless of whether the patient is pregnant or not, and that the fetal depression, although usually mild, can be correlated with fetal pH data as well as Apgar scores. In addition, this study supports indirectly the contention that metabolites of meperidine rather than the parent compound cause fetal depression. It would appear, therefore, that in certain obstetric cases with a higher probability for infant depression, other analgesic agents might be considered, especially if the serum pattern indicates meperidine is being metabolized.