Pharmacokinetic drug interactions of synthetic opiate analgesics.

Earlier reviews have covered pharmacokinetic drug interactions of natural and semi-synthetic opioid analgesics. This review will focus on the pharmacokinetic drug-drug interactions of methadone, propoxyphene, levomethadyl, meperidine, other phenylpiperidines (such as fentanyl), pentazocine, diphenoxylate, loperimide, and tramadol. The authors present an extensive review of the current literature. These drugs, with a few exceptions, are, at least partially, if not primarily, metabolized by the cytochrome P450 isoenzyme system (CYP) 3A4, and the action/interaction of these enzymes can have an effect on outcome. Therefore, these drugs are likely to produce drug-drug interactions when the CYP3A4 system is inhibited or induced. Knowledge of these drug-drug interactions is important because such interactions may decrease drug efficacy or result in adverse effects.