Hypersensitivity pneumonitis induced by nalidixic acid.

Interstitial pneumonitis developed in a patient one week after therapy with nalidixic acid was initiated. The causal association between the drug and the lung disease is based on the temporal relationship, an increased eosinophil count in both peripheral blood and fluid obtained by bronchoalveolar lavage, a positive migration inhibitory factor test with nalidixic acid, and exclusion of other causes. This is, to the best of our knowledge, the first report of a pulmonary hypersensitivity reaction to nalidixic acid.