Drμg-specific monoclonal antibodies were produced against the very small drμg hapten, 5-benzimidazolecarboxylic acid.5-Benzimidazolecarboxylic acid has been used in the preparation of: ? 1H-benzoimidazole-5-carboxylic acid benzotriazol-1-yl ester. ? piperidin-1-yl(1-m-tolyl-1H-benzo[d]imidazol-5-yl)methanone. Drug-specific monoclonal antibodies were produced against the very small drug hapten, 5-benzimidazolecarboxylic acid. 5-Benzimidazolecarboxylic acid has been used in the preparation of: ? 1H-benzoimidazole-5-carboxylic acid benzotriazol-1-yl ester. ? piperidin-1-yl(1-m-tolyl-1H-benzo[d]imidazol-5-yl)methanone.