Importance of repeat testing in the diagnosis of penicillin allergy

Abstract

Conflicts of interest: none declared. Sir, In the May 2005 issue of this Journal Lammintausta and Kortekangas‐Savolainen1 presented an interesting article about the usefulness of skin tests in determining drug hypersensitivity. We have found the results to be very helpful as there are only few reported works about the prevalence of positive skin tests in the context of allergic reactions. However, we have some points of contention. Although both patch tests (PTs) and intradermal tests (IDTs) are used for the diagnosis of nonimmediate reactions to aminopenicillins, and both tests appear to be valuable, delayed‐reading IDTs appear to be somewhat more sensitive2 than PTs, but also less specific.3 In the report by Lammintausta and Kortekangas‐Savolainen, beta‐lactam antibiotics were the drugs more often suspected and tested. However, IDTs with major and minor determinants were carried out only in 31 of 342 patients with suspected penicillin allergy and none of them elicited a positive reaction. The European Network for Drug Allergy (ENDA) recommends testing in most patients in whom penicillin allergy is suspected.4 In fact, most diagnoses of penicillin allergy have recently been reported to be obtained by means of the IDT.5, 6 Between January 2002 and June 2005 we evaluated 604 patients with suspected beta‐lactam allergy. In all of them, after written informed consent, skin prick tests and IDTs were performed with benzylpenicilloyl polylysine (PPL), minor determinants mixture (MDM; including benzylpenicillin, benzylpenicilloic acid and sodium benzylpenicilloate), penicillin G and the suspect drug if it was other than penicillin. PPL and MDM were purchased from two different companies (Allergopen®; Allergopharma, Reinbeck, Germany and Diater SA, Madrid, Spain). If the skin tests were negative, controlled drug challenge was performed under strict supervision. After 15 days the skin tests and drug challenge were repeated, as recommended by ENDA.4 After completing the study, 66 patients were diagnosed with beta‐lactam allergy, 60 by skin testing and 10 of those in the repeat tests. From 1108 challenges with beta‐lactams in 554 patients, there were only six positives following a previously negative skin test.