Isonicotinic acid hydrazide as an antigen.

Detection by in vitro serologic techniques of circulating antibody directed against isonicotinic acid hydrazide (INH, known as isoniazid) in humans has not been reported. In the past few months, however, sera from a patient with a recent history of isoniazid hypersensitivity of the immediate type have been studied, and reaginic antibodies (IgE) specific to INH were detected by means of an enzyme-linked allergosorbent test. Preliminary enzyme-linked allergosorbent tests also demonstrated that INH-specific IgE occurred in the serum of two of 150 patients with tuberculosis who had been treated with INH.