36 Muscle Relaxant Induced Allergic Reactions

BACKGROUND: Both eperisone and afloqualone act by relaxing both skeletal muscles and vascular smooth muscles to improve circulation and suppress pain reflex. These drugs are usually prescribed combined with non-steroid anti-inflammatory drugs (NSAIDs) as pain killers. Although there have been no report on serious adverse reactions to muscle relaxant, this is the first report of 3 anaphylactic reactions caused by eperisone and afloqualone. METHODS: All 3 patients had previous histories of anaphylaxis after oral intake of multiple pain killers including muscle relaxant and NSAID for chronic muscle pain. Open label oral challenge tests were performed with each drug to find out which drugs caused systemic reactions. RESULTS: All experienced the same reactions within an hour after oral intake of eperisone or afloqualone. The severity of these reactions ranged from laryngeal edema to hypotension. To confirm the systemic reaction caused by eperisone or afloqualone, skin prick testing and intradermal skin tests with eperisone or afloqualone extract were performed in vivo, and the basophil activity tests were performed with stimulation with these drugs in vitro. In one patient with laryngeal edema, intradermal test with afloqualone results showed positive result and CD63 level increased after the stimulation with afloqualone dose-dependently. CONCLUSIONS: We report 3 allergic reactions caused by oral muscle relaxants that might be mediated by non-IgE-mediated responses. As muscle relaxant, eperisone and afloqualone, commonly prescribed drugs for chronic muscle pain, can induce severe allergic reactions therefore we should prescribe them carefully.