Antibodies specific to isoniazid and isonicotinic acid.

Rabbit antisera to isoniazid (INH) and its major metabolite, isonicotinic acid (INA), were prepared by immunization with conjugates of these compounds with human serum albumin. The antisera were rendered hapten-specific by exhaustive absorption with the immunizing carrier. Purified anti-hapten antibodies were also isolated with appropriate immunosorbents. As demonstrated by inhibition of the quantitative precipitin curves and of precipitating immune complexes in immunodiffusion tests, the antibodies to the two haptens reacted with either INH or INA, and also with isonicotinamide (INC); these three related molecules share the isonicotinyl group. The relative effectiveness of inhibition by free hapten of precipitating immune complexes consisting of either anti-INH or anti-INA antibodies and the related hapten-protein conjugates was INH greater than INC greater than INA.