Allergological work up
If the drug HSR was immediate type, we performed skin testing with the culprit drug, histamine (10 mg/ml of histamine phosphate, Allergopharma) as positive and 0.9% sterile saline as negative controls on the volar surface of forearm (13, 15). If skin prick test was negative, intradermal testing (IDT) with the culprit drug starting with minimum nonirritating concentration was done and assessed after 20 minutes (15). The test was considered as positive if a wheal of at least 3 mm greater in diameter than that of saline, accompanied by erythema, was formed. The evaluation of beta-lactam allergy was based on European Academy of Allergy and Clinical Immunology recommendations for skin prick test (SPT) and intradermal test (IDT) as amoxicillin and other semi-synthetic penicillins (20 mg/mL), cephalosporins (20 mg/mL), major (benzylpenicilloyl octa-L-lysine, 0.04 mg/mL) and minor (sodium benzylpenilloate, 0.5 mg/mL) determinants (Diater S.A., Madrid, Spain) and benzylpenicillin (10 000 IU/mL). In low-risk nonimmediate reactions with beta-lactams, direct provocation with the culprit drug without prior skin testing was preferred (14). In case of delayed HSRs, delayed reading of IDT was done if applicable (13).