Life-threatening anaphylactoid reactions to muscle relaxants.

Sixty-seven patients who had life-threatening reactions to muscle relaxant drugs diagnosed by intradermal testing or challenge were studied. Six patients reacted on two occasions; four reacted to different relaxants. There was a significantly greater ratio of female-to-male patients who reacted than in a nonreacting population. Patients who reacted to muscle relaxants had an incidence of allergy, atopy, asthma, and previous reactions to anesthesia that was significantly greater than nonreacting patients, but not greater than patients who had reacted to induction agents. Eighty-five percent of patients who reacted to muscle relaxants had never previously been exposed to the drug, whereas 60% of patients reacting adversely to induction agents had been previously exposed to induction agents. The reactions were not related to additives or preservatives. In spite of a lack of previous exposure, type I hypersensitivity appears the most likely mechanism responsible for life-threatening reactions to muscle relaxants.