Correspondence to 'Hypersensitivity reactions with allopurinol and febuxostat: a study using the Medicare claims data'.

We read with great interest the article by Singh and Cleveland, which the authors reported that the observed hypersensitivity reactions (HSRs) associated with allopurinol and febuxostat were not different.1 This conclusion differs from previous studies on HSRs associated with allopurinol and febuxostat using claimed data2 and intramural databases.3 The discrepancy may arise from different inclusion criteria for the diagnosis of HSRs based on International Classification of Diseases, Ninth Revision (ICD-9) coding system, methods for identifying causative drugs, methods for stratification, as well as ethnicity of the involved population. The definition of HSR in the study by Singh and Cleveland adopted ICD-9 diagnostic codes specifying eosinophilia (288.3), HSR- associated arthropathy (713.6), anaphylactic reactions (995.0) or unspecified adverse drug effect (995.2) or allergy (995.3), plus the baseline exclusion for E930 to E949.1 On the contrary, in our previous studies, the definition of cutaneous adverse reactions (CARs) using the Taiwanese registry database involved drug-induced dermatitis (693.0), erythema multiforme (695.1) or erythematous conditions (695.89 or 695.9).2–4 Likewise, another study based on intramural database …