Buprenorphine's analgesic effect is due to partial agonist activity at mu-opioid receptors. Buprenorphine is also a kappa-opioid receptor antagonist. The partial agonist activity means that opioid receptor antagonists (e.g., an antidote such as naloxone) only partially reverse the effects of buprenorphine. The binding to the mu and kappa receptors results in hyperpolarization and reduced neuronal excitability. Furthermore, buprenorphine slowly dissociates from its receptor. This observation would account for the longer duration of action compared to morphine, the unpredictability of its reversal by opioid antagonists, and its low level of manifest physical dependence. Its receptor fixation half life is 40 minutes which is significantly longer than morphine (milliseconds).
Buprenorphine is a synthetic opioid analgesic and thebaine derivative, with a longer duration of action than morphine. Buprenorphine interacts predominately with the opioid mu-receptor. These mu-binding sites are discretely distributed in the human brain, spinal cord, and other tissues. In clinical settings, buprenorphine exerts its principal pharmacologic effects on the central nervous system. Its primary actions of therapeutic value are analgesia and sedation. Buprenorphine may increase the patient's tolerance for pain and decrease the perception of suffering, although the presence of the pain itself may still be recognized. In addition to analgesia, alterations in mood, euphoria and dysphoria, and drowsiness commonly occur. Buprenorphine depresses the respiratory centers, depresses the cough reflex, and constricts the pupils. Pharmacological effects peaks at 15 minutes and persists for 6 hours or longer when given intramuscularly. When given intravenously, the time to onset and peak effect are shortened.
Hepatic. Buprenorphine undergoes both N-dealkylation to norbuprenorphine and glucuronidation. The N-dealkylation pathway is mediated by cytochrome P-450 3A4 isozyme. Norbuprenorphine, an active metabolite and has one-fifth of the pharmacologic activity of the parent compound, can further undergo glucuronidation.
Manifestations of acute overdose include pinpoint pupils, sedation, hypotension, respiratory depression and death.