Idiosyncrasy to pyrazolone drugs.

Studies carried out in 68 patients with idiosyncratic reactions to noramidopyrine and/or aminophenazone led to distinction of two different groups. In the first group: 1) noramidopyrine, aminophenazone, phenylbutazone and sulfinpyrazone as well as several other inhibitors of cyclooxygenase, including aspirin, precipitated bronchoconstriction; 2) skin tests with pyrazolone drugs were virtually negative; 3) all patients had chronic asthma. In the second group: 1) noramidopyrine and aminophenazone induced anaphylactic shock and/or urticaria; 2) skin tests with these drugs were highly positive; 3) phenylbutazone, sulfinpyrazone and several other cyclooxygenase inhibitors, including aspirin, could be taken with impunity; 4) chronic bronchial asthma was present in only one-fourth of the patients. We suggest that the pathogenic mechanisms responsible for the idiosyncratic reactions involve inhibition of cyclooxygenase in the first group, and allergic reactions in the second group. Distinction of these two groups is of clinical importance since in individual patients it gives insight into the safe administration of pyrazolone and aspirin-like drugs.