Name: Propoxyphene (Darvon)
Class: Opioid (Synthetic-Analgesic)
Mechanism: Agonist of opioid receptors. Causes analgesia ( threshold for pain, ¯ subjective rxn), antitussive effects, euphoria/dysphoria (atypical), sedation (rarely stimulation), resp. depression, miosis, n/v, ¯ body temp., ACTH/PRO/GH, ¯ LH/TSH (hormone effects usu. non-consequential), occasionally hypotension, constipation, biliary/ureteral/bladder muscle tone, ¯ uteral muscle tone, histamine release (hypotension, urticaria, itching).
Absorption: Oral
Metabolism.: Hepatic conjug. ® polar Metabolismolites.
Excretion, t½: Urine. Duration of analgesia—4-5 hr.
Toxicity/S.E.s: Histamine release ® asthma in suscept. patients. Use w/caution w/compromised resp. patients. CO2 retention ® intracranial pressure (may mask signs of head injury). Poisoning ® coma, severe resp. depression, pinpoint pupils. Rapid onset of tolerance (up to 100x) to analgesia, euphoria/dysphoria, sedation, n/v, resp. depression, cough suppression. 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. Drug interactions—sedative hypnotics ® severe CNS/resp. depression; phenothiazines/tricyclic antidepressants ® sedation, freq. resp. depression.
Utility: Limited analgesia (no more than aspirin in usu. therapeutic dose, but augments the effects of aspirin & acetaminophen.
Special Features: Very low maximum efficacy (limited analgesia). Low addiction/abuse liability.