The rising use of β-lactam antibiotics has been accompanied by a steady increase in serious hypersensitivity reactions, including anaphylaxis. Two previously healthy adults – one exposed to oral amoxicillin–clavulanate, the other to intravenous ceftriaxone – developed fulminant anaphylaxis despite having no documented drug allergy. Within minutes, both exhibited the characteristic triad of airway obstruction, breathing difficulty and circulatory collapse. Guideline-recommended intramuscular adrenaline was administered immediately, followed by high-flow oxygen and crystalloid boluses for hypotension, with adjunctive antihistamines and corticosteroids given only after airway, breathing and circulation were stabilised. Because β-lactam-induced anaphylaxis can be IgE-mediated and may occur without a previously documented drug allergy, every front-line clinician must recognise the syndrome promptly and initiate evidence-based first-line therapy without delay.