Anaphylaxis to omeprazole

Background: Omeprazole is a non-competitive inhibitor of the parietal cell enzyme Hf-Kf-adenosine triphosphatase. To date, two cases of angioedema and urticaria and two cases of anaphylaxis from omeprazole have been published. Objective: To report a new patient with omeprazole-induced anaphylaxis demonstrated by skin tests and increased serum tryptase levels. Methods and results: Elevated serum tryptase levels (5.1 U/L) were detected 6 hours after the onset of the anaphylaxis. Skin intradermal tests were positive with omeprazole IV (4 mg/mL), omeprazole capsules diluted in saline serum (20 mg/mL), and Iansoprazole (30 mg/mL). Serum specific IgE anti-omeprazole was negative. Conclusions: According to the elevated serum tryptase levels and the positive skin test results, anaphylaxis was due to use of omeprazole. We think the adverse reaction to omeprazole was induced by an IgE-mediated hypersensitivity mechanism to omeprazole itself and not to a metabolite. We have also demonstrated crossreactivity, at least by skin tests, between omeprazole and lansoprazole.