Rifampin reduces oral morphine absorption: a case of transdermal buprenorphine selection based on morphine pharmacokinetics.

A 51-year-old male was referred to the Stratton Veterans Affairs Medical Center Pain Service after hospital admission for endocarditis with a history of heroin use and chronic low back pain. During his hospital stay he experienced a reduction in his serum morphine level ostensibly as a result of concomitant rifampin administration. We hypothesize that diminished absorption was from rifampin-mediated intestinal P-glycoprotein induction, ultimately decreasing serum free morphine and metabolites. The case became more complex in an attempt to balance managed pain, history of substance abuse, completion of antibiotic therapy, and a reasonable pain regimen upon discharge. Ultimately, the patient was titrated onto a buprenorphine transdermal patch, the initiation of which was based on serum free morphine and an extrapolated oral morphine dose by calculation.