IgE-mediated metamizol allergy and the usefulness of the cellular allergen stimulation test

Metamizol is a pyrazolone-derivative nonsteroidal anti-inflammatory drug that is commonly associated with hypersensitivity reactions. Some of these reactions are IgE-mediated and potentially severe, which limits the diagnosis based on oral drug challenge. We describe 6 selective metamizol hypersensitivity cases, regarding clinical evaluation and diagnosis management, with focus on the usefulness of skin tests and the cellular allergen stimulation test (CAST). All patients were female, aged 27 to 50 years old. All had immediate reactions after metamizol administration: 3 had anaphylaxis and 3 had urticaria and angioedema. Skin prick tests with metamizol were positive in 2 patients. Intradermal tests were positive in the remaining, all with 1/100 dilution, and elicited systemic reactions in 2 of them. CAST to metamizol was negative in all cases. The patients tolerated other nonsteroidal anti-inflammatory drugs. Skin tests proved to be a good diagnostic method to identify IgE-mediated metamizol allergy, although skin tests elicited systemic symptoms in some cases. Despite this being a small sample, our results showed a very low sensitivity for CAST which differs from data previously reported in the literature.