Penicillin skin testing: a 20-year study at the West Los Angeles Veterans Affairs Medical Center.

Penicillin (PCN) may cause a reaction in up to 10% of the population. No study has examined PCN skin testing longitudinally over a 20-year period. A total of 122 patients underwent PCN skin testing between September 1978 and May 1998. Patients were skin tested with the major determinant, penicilloyl polylysine, and three minor determinants, PCN, benzylpenilloate, and benzylpenicilloate. Ten of a total of 122 patients had positive skin test reactions. Nine reactions were to penicilloyl polylysine and one reaction was to the minor determinant benzylpenilloate. There was a total of four patients (3.6%) with false-negative results on skin testing. PCN skin testing with both the major and minor determinants should be performed when there is a history of PCN allergy, a serious illness, and no suitable alternatives. If either the major or minor determinants are positive without suitable alternative antibiotics, then the patient should undergo desensitization.