pentazocine

Pentazocine is a synthetic opioid analgesic that exhibits mixed agonist-antagonist properties. It acts as a kappa-opioid receptor agonist and as a partial agonist/antagonist at mu-opioid receptors. This pharmacological profile provides analgesia with a relatively lower risk of some mu-related adverse effects, such as respiratory depression, at typical doses, but it can still cause sedation, dependence, and withdrawal in individuals dependent on mu-opioid agonists. Pentazocine is used for the relief of moderate to severe pain when non-opioid analgesics are inadequate or inappropriate.

It is marketed both as a single-agent product and in combination with naloxone (for example, in the brand Talwin NX). The combination is intended to deter injection abuse because naloxone, when taken by mouth, has limited systemic effects, but can precipitate withdrawal if injected by an opioid-dependent person.

Pharmacokinetics and metabolism vary with route of administration. After oral dosing, onset of analgesia typically occurs within 15 to 60 minutes, with a duration of about 3 to 4 hours. Pentazocine is primarily metabolized by the liver and its metabolites are excreted in the urine.

Common adverse effects include sedation, dizziness, nausea, vomiting, sweating, and anxiety or dysphoria. Other reported effects can include tachycardia, hypertension, and, less commonly, hallucinations or confusion. Cautions are advised in patients with respiratory disorders, head injury or increased intracranial pressure, biliary tract disease, and in those who are pregnant, where benefits must be weighed against risks. It may precipitate withdrawal in individuals dependent on mu-opioid agonists.