Anaphylaxis to proton pump inhibitors

Proton pump inhibitors (PPI) are widely used for the treatment of peptic ulcer, but cases of anaphylactic reactions have rarely been described. We present a patient who experienced an episode of urticaria 30 minutes after oral intake of an omeprazole capsule. Skin prick tests to omeprazole, pantoprazole and lansoprazole were positive. Challenge test with lansoprazole was carried out and within 45 minutes the patient developed urticaria, facial edema, vomiting, and hypotension. Oral challenge with other imidazole derivatives (ketoconazole, cimetidine, metronidazole) were carried out with good tolerance. Serum tryptase levels determined 3 hours after the adverse reaction to lansoprazole were elevated. Specific IgE to PPI were not detected by an enzyme-linked immunosorbent assay technique. The clinical findings, positive skin prick test to PPI and elevated serum tryptase levels suggest that an IgE-mediated mechanism was implicated in the reactions to both omeprazole and lansoprazole. Skin prick tests may be a useful tool for detecting patients sensitized to PPI. An experimental protocol was used to detect specific IgE antibodies against PPI, which may explain RAST negativity. The previous findings suggest that cross-reactivity between PPI exists, but not with other imidazoles.