Absorption high extraction ratio drugs

In common with other phenolic opiate analgesics, buprenorphine shows low peroral potency, suggesting a high first-pass metabolism effect indeed, work in rats has shown this to be the case. Intravenous studies have estimated that the extraction ratio of buprenorphine is 85% and that peroral systemic availability is consequently expected to be 15% or less. Although absorption from the mouth is slow and, therefore, not as useful as parenteral administration in the treatment of acute pain, it offers a major bioavailability advantage over the peroral route for this drug. If required, the patient can be given a parenteral dose of buprenorphine to achieve rapid pain relief and... 

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