D1.49 - Crossed-reactivity among Proton Pump Inhibitors in Immediate Severe Hipersensitivity Reactions

Although proton pump inhibitors (PPIs) has low incidence of severe immediate hypersensitivity reactions, they are not exent of risks. These reactions are more often caused by drug-selective or group-selective crossreactions, being cross-reactivity to all PPIs less frequent.

A 29-year-old male experienced an immediate Grade IV anaphylactic reaction (according to WAO classification) after taking the first oral dose of Omeprazole 20mg for gastrointestinal reflux treatment. The reaction included palmoplantar itching, urticaria, uvular edema, disnea, wheezing and dizziness, oxygen desaturation to 85% and hypotension; it was resolved in the emergency department following intravenous administration of Urbasón and Polaramine, together with subcutaneous adrenaline administration.

Considering the severity of the reaction, a basophil activation test (BAT) was perferomed for all PPIs group (Omeprazole, Lansoprazole and Pantoprazole), prior to considering an oral challenge test with PPIs different to Omeprazole.

BAT for Omeprazole, Lansoprazole and Pantoprazole at different concentrations (0,02 mg/mL, 0,2 mg/mL, 2 mg/mL ) showed a positive result for all of them. The percentage of degranulated basophils (%CD63+) was >5%, and the saturation index (SI) calculation was >2 confirming cross-reactivity to all PPIs.

PPIs are the most portent drugs used for inhibiting gastric acid secretion. Eventough they are generally safe and have a low incidence of hypersensitivity reactions, cross-reactivity among all PPI groups exists. Although cross-reactivity is usually studied using skin test, its sensitivity may not be high enough. Some studies reported that BAT may have higher sensitivity than skin test, with positive predictive value of 100% and similar specificity with negative predictive value of 67,7%. Therefore, in those cases with severe anaphilactic reaction, we recommend performing BAT for all PPIs prior oral challenge testing with alternatives to exclude complete cross-reactivity.