Severe anaphylactic reaction to metamizol during subarachnoid anesthesia

A 59-year-old man with no relevant medical history underwent a right saphenectomy under subarachnoid anesthesia with mepivacaine. Administration of intravenous metamizol for postoperative analgesia was followed by severe anaphylactic reaction with respiratory failure and ventricular fibrillation. The patient recovered after orotracheal intubation and defibrillation. High serum tryptase levels 2 and 6 hours after the episode and positive skin prick tests confirmed the diagnosis of anaphylactic reaction mediated by immunoglobulin-E antibodies. Anaphylactic reactions to metamizol may be more common than would appear based on reports in the literature. When signs present suddenly with cardiovascular or respiratory involvement, symptomatic treatment should be started even in the absence of cutaneous or mucosal signs and allergy tests should be carried out immediately.