The facts about penicillin allergy: a review.

Hypersensitivity reactions are the major problem in the use of penicillins. True penicillin allergy is rare with the estimated frequency of anaphylaxis at 1-5 per 10 000 cases of penicillin therapy. Hypersensitivity is however, its most important adverse reaction resulting in nausea, vomiting, pruritus, urticaria, wheezing, laryngeal oedema and ultimately, cardiovascular collapse. Identification of patients who erroneously carry ß-lactam allergy leads to improved utilization of antibiotics and slows the spread of multiple drug-resistant bacteria. Cross-reactivity between penicillin and second and third generation cephalosporin is low and may be lower than the cross-reactivity between penicillin and unrelated antibiotics.