Penicillin allergy.

Although many new antibiotics are available, penicillin and its many semisynthetic derivatives are first-line drugs for many infections. These agents are relatively nontoxic even at high doses; however, their use frequently leads to allergic reactions. Withholding penicillin therapy from patients at high risk of allergic reaction to it is the most effective means of preventing such occurrences. Because immunoglobulin E-mediated reactions account for significant mortality and morbidity in association with penicillin use, the thrust of research on penicillin allergy has been to prevent such reactions. The many risk factors associated with subsequent immunoglobulin E-mediated penicillin allergy include history, timing and nature of previous penicillin exposure and/or allergy, age, route of administration, and response to skin testing with major and minor determinants of penicillin. The relative predictive values of each are discussed. Cross-reactivity between penicillin and its many analogs is reviewed and an approach to the patient who has a positive history for penicillin allergy and is in need of penicillin is offered.