Metabolites of meperidine related to fetal depression

Three specific patterns of meperidine metabolism were observed in the maternal serum of 52 patients studied. These patterns appear to be related to the rate of formation of certain metabolites of the compound. No observable signs of infant depression were detectable when delivery was performed during the first 60 minutes following the administration of the analgesic agent regardless of the type of pattern. However, when greater than 60 minutes had elapsed following intravenous injection of meperidine the incidence of depressed infants was directly related to the more rapid metabolic patterns. Therefore, the most significant factors relating infant depression to meperidine are the maternal metabolic pattern and the length of time the patient is in labor following the administration of the compound. These observations presumably reflect the increased toxicity of certain metabolites of meperidine transferred to the fetus from the mother. Thus, if delivery takes place within 60 minutes after injection, the level of metabolites of meperidine in the fetus should be low and the chance of a depressed infant reduced.