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| Formula | C23H31NO |
| Molar mass | 337.507 g·mol−1 |
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Xorphanol (INN; also known asxorphanol mesylate (USAN); developmental codesTR-5379 orTR-5379M) is anopioidanalgesic of themorphinan family that was never marketed.[1][2][3]
Xorphanol is a mixedagonist–antagonist ofopioid receptors,[4][5][6] acting preferentially as a high-efficacypartial agonist/near-full agonist of theκ-opioid receptor (Ki = 0.4 nM;EC50 = 3.3 nM;Imax = 49%;IA = 0.84)[7][8][9] and to a lesser extent as apartial agonist of theμ-opioid receptor (Ki = 0.25 nM;IC50 = 3.4 nM;Imax = 29%) with lower relativeintrinsic activity and markedantagonistic potential (including the ability to antagonizemorphine-induced effects and induceopioid withdrawal inopioid-dependent individuals).[3][10] The drug has also been found to act as an agonist of theδ-opioid receptor (Ki = 1.0 nM; IC50 = 8 nM;Imax = 76%).[11]
Xorphanol produces potent analgesia, and was originally claimed to possess a minimal potential fordependence orabuse.[12][13][14] Moreover,side effects inanimal studies were relatively mild, with onlysedation andnausea being prominent, although it also producedconvulsions at the highest dose tested.[15] However, human trials revealed additional side effects such asheadaches andeuphoria, and this was the subject of a lawsuit between the drug's inventors and the company to which they had licensed the marketing rights, which claimed that these side effects had not been revealed to them during the license negotiations.[16] As a result of this dispute, the drug was never marketed commercially.