Name: Pentazocine (Talwin)
Class: Opioid (Synthetic-Analgesic)
Mechanism: Mixed agonist-antagonist of opioid receptors. Causes analgesia ( threshold for pain, ¯ subjective rxn), sedation, resp. depression.
Absorption: IM, subcut, oral (1st pass Metabolism ® med. oral:parenteral potency).
Metabolism.: Hepatic conjug.®polar Metabolismolites. Excretion, t½: Urine. Duration of analgesia—3-4 hr.
Toxicity/S.E.s: CO2 retention ® intracranial pressure (may mask signs of head injury). Tolerance (up to 100x) to analgesia, sedation, resp. depression. Physical dependence—abrupt w/drawal ® rhinorrhea, lacrimation, chills, goose pimples, hyperventilation, mydriasis, myalgia, vomiting, diarrhea, anxiety, hostility (but it’s not fatal). Also psychological dependence. Precipitates w/drawal synd. Large doses ® dysphoria & hallucinations. Drug interactions—sedative hypnotics ® severe CNS/resp. depression; phenothiazines/tricyclic antidepressants ® sedation, freq. resp. depression.
Utility: Analgesia. Orig. thought to lack abuse liability.
Special Features: Mod. maximum efficacy. Low addiction/abuse liability. Psych. dependence.