Rational use of sublingual opioids in palliative medicine.

The sublingual administration of opioid analgesics has been a mainstay in the pain management of homebound dying hospice patients who are no longer able to swallow. It is also a potentially useful route of administration in other situations in which the oral route is not available and other routes are impractical or inappropriate. Potential advantages of the sublingual route include rapid analgesic onset and avoidance of hepatic first-pass metabolism. Pharmacokinetic and pharmacodynamic studies have yielded widely disparate data on sublingual morphine. Other opioids have been less studied. Available data suggests limited sublingual availability of hydrophilic opioids (e.g., morphine, oxycodone, and hydromorphone) and superior absorption of the lipophilic opioids (e.g., methadone and the fentanils). Buprenorphine, a potent, lipophilic, partial mu-opioid receptor agonist, appears promising but awaits further study.