Bioavailability, Metabolism, and Excretion
The bioavailability of buprenorphine varies depending on the route of administration. When taken orally, buprenorphine is very rapidly metabolized and as a result has poor bioavailability (Chiang and Hawks 2003). But when taken sublingually, buprenorphine's bioavailability is significantly better.
Sublingual monotherapy tablets have been shown to produce peak concentrations of 62% of the solution after 7 days, whereas sublingual combination therapy films or tablets (i.e. Suboxone) produced a peak concentration of 82% of the solution after 7 days (Strain et al. 2004). Such findings suggests that the presence of naloxone acts to increase the availability of buprenorphine in the body, thus supporting the use of combination buprenorphine/naloxone in office-based opioid treatment. The combination formulation is now used with all patients, with few exceptions (pregnant patients and those with naloxone allergies).
Buprenorphine is primarily metabolized in the gastrointestinal tract and the liver, using the CYP 3A4 system. Medications that inhibit CYP 3A4 may increase plasma concentration of buprenorphine and potentially call for a lower daily dose of buprenorphine. Medications that induce CYP 3A4 activity can decrease buprenorphine's plasma concentration and potentially require a higher daily dose of buprenorphine.
Most buprenorphine metabolites are excreted fecally rather than renally (Chiang and Hawks 2003); as a result, buprenorphine is relatively safe for patients with renal insufficiency.