Patch testing in the investigation of non-immediate cutaneous adverse drug reactions to metamizole.

Metamizole [INN; dipyrone (BAN, USAN)] is a pyrazolone derivative and one of the most commonly prescribed analgesics worldwide (1). Along with non-steroidal anti-inflammatory drugs (NSAIDs), metamizole is very frequently involved in hypersensitivity reactions (2). Immunologically mediated hypersensitivity reactions to metamizole can be immediate (IgE-mediated) or non-immediate (T cell-mediated) (2, 3). Although immediate cutaneous adverse drug reactions (CADRs) are frequent and well known, non-immediate CADRs to metamizole, other than fixed drug eruptions, are less common and have been poorly described in the literature (3, 4). The usefulness of patch testing in the investigation of non-immediate CADRs to metamizole has not been extensively studied. The following study was performed to evaluate the value of patch testing in the setting of non-immediate CADRs imputable to metamizole.