Mephenesin (INN), also called myanesin,[1][2] is a centrally acting muscle relaxant. It can be used as an antidote for strychnine poisoning. Mephenesin however presents with the major drawbacks of having a short duration of action and a much greater effect on the spinal cord than the brain, resulting in pronounced respiratory depression at clinical doses and therefore a very low therapeutic index. It is especially dangerous and potentially fatal in combination with alcohol and other depressants.[3] Mephenesin was the inspiration for the synthesis of a derivative of 1,3-propanediol, meprobamate, by Bernard Ludwig and Frank Berger,[4] the first tranquilizer to see widespread clinical use. Mephenesin is no longer available in North America but is used in Italy and a few other countries.[5] Its use has largely been replaced by the related drug methocarbamol, which is better absorbed.[6]
Mephenesin may be an NMDA receptor antagonist.[7] Mephenesin was previously used in France as an OTC muscle relaxant called Décontractyl but was taken out of production by Sanofi Aventis and due to a French Health Ministry decree in July 2019. Mephenesin is, however, still available in Italy.
Bachmeyer C, Blum L, Fléchet M, Duriez P, Cabane J, Imbert J (1996). "[Severe contact dermatitis caused by mephenesin]". Ann Dermatol Venereol. 123 (3): 185–7. PMID8761781.
Ono H, Nakamura T, Ito H, Oka J, Fukuda H (1987). "Rigidity in rats due to radio frequency decerebration and effects of chlorpromazine and mephenesin". Gen Pharmacol. 18 (1): 57–9. doi:10.1016/0306-3623(87)90170-4. PMID3557053.