Although rare, anaphylactic reactions induced by proton pump inhibitors have been reported. The presence of cross-reactivity between different members of the group is not clear.
We studied 9 patients with adverse reactions to omeprazole. Clinical symptoms appeared immediately in 8 patients and after 4 hours in 1.
Symptoms ranged from urticaria/angioedema in 7 cases to anaphylaxis in 2 cases. Skin prick tests and oral controlled challenge tests with omeprazole, lansoprazole, and pantoprazole were performed.
Skin prick or intradermal tests with omeprazole were positive in 8 patients. Four were also positive to pantoprazole. Prick tests with lansoprazole were always negative. Lansoprazole was administered to all 9 patients, with good tolerance in 8. Only 3 patients were challenged with pantoprazole and developed widespread urticaria.
We present 9 patients with immunoglobulin E–mediated allergy to omeprazole. In most of our cases, lansoprazole proved to be a good alternative treatment.

Key words: Proton pump inhibitors. Omeprazole. Lansoprazole. Drug allergy. Cross-reactivity.