Clinical features of immediate hypersensitivity to isopropylantipyrine.

Hypersensitivities induced by isopropylantipyrine (IPA), a pyrazolone derivative within the wider family of non-steroidal anti-inflammatory drugs (NSAIDs), are rarely reported. We characterized the clinical features of 12 patients with IPA-induced hypersensitivity. Twelve patients with immediate hypersensitivity to IPA were enrolled and classified into two groups: group I, consisting of eight patients (66.7%) with selective hypersensitivity; and group II, consisting of four patients (33.3%) showing cross-intolerance to other NSAIDs. Skin prick and intradermal and oral provocation tests with IPA were performed. To confirm selective hypersensitivity, an aspirin oral provocation test was also conducted. The most common manifestations were cutaneous reactions (91.7%), followed by anaphylaxis (66.7%), respiratory (41.7%), ocular (16.7%), and gastrointestinal reactions (16.7%). The median age and the median age at onset were 34.5 (range, 23-55) years and 28.0 (range, 7-47) years, respectively. In both groups I and II, all patients showed negative responses to skin prick testing, whereas only two patients in group I were positive in response to intradermal IPA tests. The response time after drug exposure was shorter in group I than in group II. Here, we report on two types of IPA hypersensitivity: selective and cross-intolerant NSAID hypersensitivity. An immediate IgE-mediated reaction may be involved in patients with selective hypersensitivity, whereas a cyclooxygenase-1-related inhibition mechanism may be a responsible mechanism for the patients with cross-intolerance to multiple NSAIDs.