Source of Support: None, Conflict of Interest: None
Two cases with mean age of 66 years were put on antituberculosis drugs containing isoniazid, rifampicin and ethambutol. Both of them exhibited a high grade isoniazid induced pyrexial response. This drug induced fever was thought to be both due to idiosyncratic reaction and the cidal effect of antituberculosis drugs containing isoniazid on the tubercle bacilli contained in the macrophages leading to release of endogenous pyrogens. Impaired immune response in the old age also may have a role to play.