Buprenorphine is a partial opioid agonist used for management of severe pain that is not responsive to alternative treatments. Also used for maintenance treatment of opioid addiction. It is a weak partial mu-opioid receptor agonist and a weak kappa-opioid receptor antagonist used for the treatment of severe pain. It is also commonly used as an alternative to methadone for the treatment of severe opioid addiction. Buprenorphine acts as a partial mu-opioid receptor agonist with a high affinity for the receptor, but lower intrinsic activity compared to other full mu-opioid agonists such as heroin, oxycodone, or methadone. This means that buprenorphine preferentially binds the opioid receptor and displaces lower affinity opioids without activating the receptor to a comparable degree. This effect can be beneficial, however, as dose-related side effects such as respiratory depression, sedation, and intoxication also plateau at around 32mg, resulting in a lower risk of overdose compared to methadone and other full agonist opioids. It also means that opioid-dependent patients do not experience sedation or euphoria at the same rate that they might experience with more potent opioids, improving quality of life for patients with severe pain and reducing the reinforcing effects of opioids which can lead to drug-seeking behaviours. Treatment of opioid addiction with buprenorphine, methadone, or slow-release oral morphine (SROM) is termed Opioid Agonist Treatment (OAT) or Opioid Substitution Therapy (OST). The intention of substitution of illicit opioids with the long-acting opioids used in OAT is to prevent withdrawal symptomns for 24-36 hours following dosing to ultimately reduce cravings and drug-seeking behaviours. Use of OAT is also intended to improved social stabilization including a reduction in crime rates, marginalization, incarceration, and use of illicit substances such as heroin or fentanyl. Buprenorphine binds to mu opioid receptors, stimulating the exchange of GTP for GDP on the G-protein complex. As the effector system is adenylate cyclase and cAMP located at the inner surface of the plasma membrane, opioids decrease intracellular cAMP by inhibiting adenylate cyclase. Subsequently, the release of nociceptive neurotransmitters such as GABA is inhibited. Opioids close N-type voltage-operated calcium channels and open calcium-dependent inwardly rectifying potassium channels. This results in hyperpolarization and reduced neuronal excitability.

Buprenorphine Pathway (New) References