Unexpected Anaphylaxis from Amoxicillin–Clavulanate in a Hospitalized Patient: A Case Report

Abstract

Background: Amoxicillin–clavulanate is a widely prescribed broad-spectrum antibiotic. Although generally well-tolerated, it can rarely cause life-threatening anaphylaxis. Prompt recognition and timely management are essential to prevent serious outcomes. Case Presentation: A 60-year-old female presented with a left breast lump and was admitted for evaluation. She had no known history of allergies or adverse drug reactions. During hospitalization, she received prophylactic intravenous amoxicillin–clavulanate, and within five minutes, she developed generalized pruritus, dyspnea, hypotension (BP: 80/50 mmHg), and tachycardia (HR: 120 bpm), consistent with anaphylaxis. Immediate management included oxygen therapy, intravenous fluids, adrenaline, hydrocortisone, antihistamines, and bronchodilators, leading to rapid clinical stabilization. The Naranjo Adverse Drug Reaction Probability Scale indicated a probable causal relationship for amoxicillin–clavulanate.The patient recovered completely with no recurrence during a 48-hour observation period. She was counseled on avoidance of β-lactam antibiotics, advised to undergo allergy testing, and educated on emergency preparedness, including the use of an epinephrine auto-injector. Discussion: Anaphylaxis due to β-lactam antibiotics is primarily IgE-mediated, with both amoxicillin and clavulanic acid acting as potential allergens. Structured causality assessment using validated tools like the Naranjo scale, adherence to international anaphylaxis management guidelines, and comprehensive patient counseling are critical for preventing recurrence. Recognition of clavulanic acid as an independent allergen is also essential to guide future therapy and avoid mislabeling of penicillin allergy. Conclusion: This case underscores the importance of early recognition, structured causality evaluation, guideline-based management, and patient education in amoxicillin–clavulanate–induced anaphylaxis, even in patients without prior allergy history.