Penicillin allergy: a practical approach to management.

Although penicillin is nontoxic, it is highly immunogenic and is the most common drug that causes allergic reactions. A previous reaction to penicillin has been shown to be unreliable in predicting sensitivity in 75% to 90% of patients. To more accurately test for penicillin allergy, diagnostic skin test reagents have been developed; these include the major determinant (benzylpenicilloyl-polylysine) and the minor determinant mixture (penicillin G potassium, benzylpenicilloate sodium and benzylpenicilloyl-N-propylamine). Penicillin skin testing has been shown to be safe and useful in predicting immediate IgE-mediated reactions (overall predictive value 99%). Reactions that occur when patients are challenged with penicillin are mild or accelerated urticarial reactions. We outline a practical and rational therapeutic approach based on the current understanding of penicillin allergy.