Evaluation of suspected delayed-type allergy to beta-lactam antibiotics: a 6-year retrospective single center experience.

BACKGROUND AND OBJECTIVES: As allergies against beta-lactam antibiotics (BLA) are among the most common drug allergies, diagnostic testing is essential when an allergic reaction is suspected. To investigate the outcomes of allergy testing in patients with delayed-type allergy to BLA. PATIENTS AND METHODS: The prevalence of delayed-type allergy to aminopenicillins or other BLA as well as their cross-reactivity, were analyzed by using skin testing (patch, prick, intradermal tests) and drug challenge testing (DCT). RESULTS: Aminopenicillins were the most frequently suspected culprit drugs in the evaluated cohort (n = 487), and delayed-type allergy was confirmed in 29.9% of patients. DCT was positive despite negative skin test results in 6.0% (29/487). Cross reactivity with closely related BLA groups were found in 10% (8/80) of patients. Given that 88.9% (297/334) of patients with previous negative skin test results tolerated the subsequent drug challenge without allergic reaction, the negative predictive value of skin testing appears reliable within a standardized clinical setting. CONCLUSIONS: Thorough allergy diagnostic testing prevents re-exposure to culprit drugs and enables the delabeling of patients with suspected drug allergy, thereby avoiding unnecessary treatment restrictions. Allergy testing is therefore an important and effective component of the diagnostic workup following a history of maculopapular exanthema.