The clinical relevance of the drug displacement interaction between meperidine and bupivacaine.

The effect of meperidine at two clinically relevant concentrations (0.4 and 0.8 microgram/ml) on the serum protein binding of bupivacaine was studied. The serum protein binding profile for meperidine was characterized over a wide concentration range (0.5-100 micrograms/ml). All bupivacaine binding experiments were characterized by a two classes of binding sites model. Bupivacaine binding was independent of added meperidine. Meperidine binding was characterized by a one class of binding sites model and the unbound meperidine concentration was relatively constant over the entire range studied. The capacity and affinity of the meperidine binding site are suggestive of binding primarily to albumin. At clinically encountered meperidine concentrations, no increased toxicity due to an increase in unbound bupivacaine would be expected.