Immediate allergic hypersensitivity to paracetamol

Introduction. - Paracetamol is an analgesic used in the general population with few side-effects. However, rare anaphylactic reactions to this molecule have been reported, for which allergy workups were usually negative, in contrast with our case. Case report. - A 19-year-old atopic male patient presented generalized urticaria with facial angioedema, dyspnea and loss of consciousness in November 2017, one hour after ingestion of a single dose of paracetamol 1000 mg. Symptoms improved within 30 min under oral antihistamine and prednisolone. Before and since this reaction, nonsteroidal anti-inflammatory drugs were tolerated by the patient. In October 2018, an immediate-reading prick-test (10 mg/mL) and an intradermal test (IDT) 10(-2) (0.1 mg/mL) performed with paracetamol were negative. Oral intake of paracetamol 50 mg was well tolerated. A second series of skin tests was performed one month later and a paracetamol prick-test and IDT were positive. A basophil activation test (BAT) was positive at 40% in the presence of paracetamol (negative control 2% and positive control 93%). The BAT was negative in a control patient. In February 2019, a third series of skin tests with paracetamol was performed: a prick-test and IDT 10(-2) were negative, but an IDT 10(-1) (1 mg/mL) was positive. A labial challenge paracetamol test using paracetamol prick solution was well tolerated. One hour after an oral drug challenge with 1000 mg, the patient developed chest urticaria and cough with no other systemic symptoms. He recovered rapidly with intravenous antihistamine (dexchlorpheniramine). Serum tryptase was normal at 90 min. Discussion. - Allergic hypersensitivity to paracetamol was diagnosed and future intake of paracetamol was contraindicated. The absence of severe symptoms could account for the normal serum tryptase value during the last reaction. Conclusion. - We report herein a rare case of immediate allergic hypersensitivity to paracetamol with a positive IDT and basophil activation test. BAT for paracetamol could be a reliable diagnostic tool in conjunction with skin tests and clinical history. (C) 2019 Published by Elsevier Masson SAS.