Proton pump inhibitors and H2 receptor antagonists, which are commonly used to treat peptic ulcer and gastroesophageal reflux diseases, are associated with a low incidence of adverse reactions. We report 3 cases of anaphylactic reactions induced by lansoprazole or ranitidine diagnosed in a population of 8304 first-referral patients
over a 13-year period. Cutaneous sensitivity to famotidine, ranitidine, omeprazole, pantoprazole, and lansoprazole was evaluated by skin prick tests with a concentration of 10 mg/mL (at 1:1000, 1:100, 1:10 and 1:1 dilutions), and if they were negative, intradermal skin tests were performed with the same dilutions of the extracts. Single-blind, placebo-controlled oral provocation tests were performed with lansoprazole, omeprazole, famotidine, and ranitidine in 2 cases. One case involved anaphylaxis during an oral provocation test with lansoprazole, and 2 cases were anaphylactic reactions to ranitidine. In both cases the skin test was positive for ranitidine and in 1 case an oral
provocation test was also positive. The second patient refused that test. Cross reactivity to other H2 receptor antagonists was not demonstrated and a safe alternative drug was found for all 3 patients. Although incidences of anaphylactic reactions induced by proton pump inhibitors or H2 reactions are rare, they can be life threatening.

Key words: Anaphylactic reaction. Proton pump inhibitors. Histamine H2 antagonists.