From Anaphylaxis to Arrhythmia: A Case Report of Fexofenadineinduced Bradyarrhythmia

Anaphylaxis is a rapid, potentially fatal systemic hypersensitivity reaction, with adrenaline recommended as first-line treatment, followed by beta-2-agonists, glucocorticoids, and antihistamines. H1-antihistamines play a limited role but help relieve skin symptoms; undue side effects, such as sedation decrease with newer generations. Fexofenadine, a third-generation antihistamine, is preferred for its non-sedative profile and lack of anticholinergic or adrenergic effects. It reaches peak plasma levels in 2-4 hours, lasts 12-24 hours, and is 60-70% protein-bound with a half-life of 11-15 hours. As a terfenadine metabolite, it avoids QT prolongation and is considered safe. This is a rare case of sinus bradycardia following fexofenadine use in a 35-year-old female with no known comorbidities, who presented with angioedema and anaphylactic shock after taking cefixime and aceclofenac. She was stabilised with intravenous hydrocortisone and intramuscular adrenaline, then admitted to the Intensive Care Unit (ICU). Fexofenadine 180 mg twice daily and hydrocortisone 100 mg thrice daily were initiated. After three doses of fexofenadine, the patient developed worsening bradycardia, with a lowest recorded heart rate of 30 bpm. No other triggers were identified. Fexofenadine was discontinued, and symptomatic treatment included atropine and oral orciprenaline. Her heart rate stabilised without requiring pacing. Bradycardia resolved within three days of stopping fexofenadine, and orciprenaline was discontinued. The patient was discharged after a week. This case highlights a rare but significant adverse effect of fexofenadine, a commonly prescribed antihistamine. Clinicians should be aware of its potential to cause bradyarrhythmia and exercise caution when prescribing, especially in acute care settings.