Treating opioid-induced constipation in patients taking other medications: Avoiding CYP450 drug interactions

When patients fail other treatment regimens and still suffer from pain sufficiently severe, opioid analgesics are appropriate and required. Unfortunately, constipation is a common adverse effect of opioids. Opioid-induced constipation (OIC) can be treated with one of the new peripherally acting µ-opioid receptor antagonist (PAMORA) agents. We summarize the mechanism of action of these drugs, with an emphasis on comparison of their potential for metabolic drug interactions.

Internet sources were searched for English-language abstracts related to the topic. Emphasis was placed on the mechanism of the PAMORAs, their metabolic pathways, drugs co-administered with opioids and potential drug-drug interactions (particularly at the level of CYP450 isozyme drug metabolism). Each source was evaluated and synthesized into the review.

PAMORAs dose-dependently antagonize the access of agonist molecules to opioid receptors, thereby directly eliminating or reducing OIC. But they differ from other opioid antagonists in that they are restricted to the periphery. Hence, they block constipation, but leave central opioid receptor-mediated pain relief undiminished. The PAMORAs have similar efficacy and safety profiles, but many pain patients have comorbidities and thus are taking other medications, which increases the potential for metabolic drug interactions.

Managing OIC in patients who have failed OTC or other therapies can be accomplished using a PAMORA, but healthcare providers must make prudent decisions that avoid or at least mitigate the potential for metabolic drug interactions in those patients with other comorbidities being managed medically by rational polypharmacy strategies.