A rare case: anaphylaxis due to chlorpheniramine maleate

Introduction
Chlorpheniramine maleate is a first-generation H1-antihistamine widely used in the treatment of urticaria, rhinitis, and conjunctivitis. Although antihistamines are generally used to control allergic reactions, they may rarely cause hypersensitivity reactions themselves.

Aim
This case report aims to raise awareness of antihistamine hypersensitivity by presenting a case of anaphylaxis following chlorpheniramine administration.

Case report
A 14-year-old male received an intravenous infusion of chlorpheniramine maleate (10 mg IV) at an external/outpatient center/facility for complaints of nausea, vomiting, and mild abdominal pain. Within approximately 5 min, he developed generalized urticaria, periorbital angioedema, cough, and hoarseness. The infusion was immediately stopped, and intramuscular adrenaline was administered. His vital signs were stabilized. The skin prick test (chlorpheniramine 1 mg/ml) was negative. However, an intradermal test diluted at a concentration of 1 : 100 showed a reaction initially 6 × 6 mm, increasing to 14 × 11 mm with surrounding hyperemic induration at 20 min, and was considered positive. A provocation test with cetirizine was planned as a safe alternative.

Conclusions
Antihistamine hypersensitivity is a rare and often overlooked condition. As there is a risk of cross-reaction among antihistamines within the same class, skin and provocation tests play a critical role in diagnosis. Identifying at least one safe alternative to antihistamine is crucial in patient management.