Isoniazid-KLH is a hapten–carrier protein conjugate generated by chemically coupling Isoniazid to keyhole limpet hemocyanin (KLH), in which Isoniazid acts as a low-molecular-weight hapten that cannot induce an immune response on its own and must be conjugated to a macromolecular carrier protein to become immunogenic, thereby enabling its use in antibody generation, immunological detection systems, and experimental studies focused on drug-specific immune recognition and assay development.