Penicillin allergy and the relevance of epicutaneous tests.

Epicutaneous tests with penicillins are important in the evaluation of penicillin allergy in patients who have shown a delayed urticarial or maculo-papular rash after the administration of penicillin derivatives. Of 23 patients who showed positive epicutaneous tests only 5 also showed immediate-type reactivity upon subsequent intracutaneous tests with the major determinant of penicillin. Moreover, patients with positive epicutaneous tests were evidently immunologically reactive on penicillins, since lymphocytes from 14 out of 17 patients showed increased DNA synthesis induced by penicillin G and ampicillin in vitro. The performance of epicutaneous tests with various penicillin derivatives is recommended as a first step in establishing penicillin allergy, because it is a safe method and because an extra group of sensitized patients is detected.