Norpropoxyphene is a major metabolite of the opioidanalgesic drug dextropropoxyphene,[1] and is responsible for many of the side effects associated with use of this drug, especially the unusual toxicity seen during dextropropoxyphene overdose.[2][3][4] It has weaker analgesic effects than dextropropoxyphene itself, but is a relatively potent pro-convulsant and blocker of sodium and potassiumchannels,[5] particularly in heart tissue,[6][7] which produces prolonged intracardiac conduction time and can lead to heart failure following even relatively minor overdoses.[8][9][10][11] The toxicity of this metabolite makes dextropropoxyphene up to 10 times more likely to cause death following overdose compared to other similar mild opioid analgesics,[12] and has led to dextropropoxyphene being withdrawn from the market in some countries.[13]
Because norpropoxyphene has a long half-life in the body of up to 36 hours (compared to around 6–12 hours for dextropropoxyphene), it can accumulate in tissues during chronic use of dextropropoxyphene-containing medications, especially in people whose excretion of drugs is slower than normal such as young children, the elderly, and individuals with reduced kidney or liver function, and so side effects including serious adverse events are more common in these groups and use of dextropropoxyphene should be avoided where possible.[14][15][16]
^Somogyi AA, Menelaou A, Fullston SV (October 2004). "CYP3A4 mediates dextropropoxyphene N-demethylation to nordextropropoxyphene: human in vitro and in vivo studies and lack of CYP2D6 involvement". Xenobiotica; the Fate of Foreign Compounds in Biological Systems. 34 (10): 875–87. doi:10.1080/00498250400008371. PMID15764408. S2CID7680532.
^Gustafson A, Gustafsson B (1976). "Acute poisoning with dextropropoxyphene. Clinical symptoms and plasma concentrations". Acta Medica Scandinavica. 200 (4): 241–8. doi:10.1111/j.0954-6820.1976.tb08226.x. PMID983792.
^Nickander RC, Emmerson JL, Hynes MD, Steinberg MI, Sullivan HR (August 1984). "Pharmacologic and toxic effects in animals of dextropropoxyphene and its major metabolite norpropoxyphene: a review". Human Toxicology. 3 Suppl: 13S–36S. doi:10.1177/096032718400300103. PMID6090306. S2CID1333582.
^Nickander R, Smits SE, Steinberg MI (January 1977). "Propoxyphene and norpropoxyphene: pharmacologic and toxic effects in animals". The Journal of Pharmacology and Experimental Therapeutics. 200 (1): 245–53. PMID13200.
^Lund-Jacobsen H (March 1978). "Cardio-respiratory toxicity of propoxyphene and norpropoxyphene in conscious rabbits". Acta Pharmacologica et Toxicologica. 42 (3): 171–8. doi:10.1111/j.1600-0773.1978.tb02187.x. PMID580345.
^Lawson AA, Northridge DB (1987). "Dextropropoxyphene overdose. Epidemiology, clinical presentation and management". Medical Toxicology and Adverse Drug Experience. 2 (6): 430–44. doi:10.1007/BF03259877. PMID3323775. S2CID13452948.
^Gibson TP, Giacomini KM, Briggs WA, Whitman W, Levy G (May 1980). "Propoxyphene and norpropoxyphene plasma concentrations in the anephric patient". Clinical Pharmacology and Therapeutics. 27 (5): 665–70. doi:10.1038/clpt.1980.94. PMID7371364. S2CID24099122.
^Inturrisi CE, Colburn WA, Verebey K, Dayton HE, Woody GE, O'Brien CP (February 1982). "Propoxyphene and norpropoxyphene kinetics after single and repeated doses of propoxyphene". Clinical Pharmacology and Therapeutics. 31 (2): 157–67. doi:10.1038/clpt.1982.25. PMID7056023. S2CID38421623.