A synthetic reagent, N-2,6 -dimethylphenye-2,3-dichloromalimide was used in the spectrophotometric estimation of isoniazid in the presence of its expected degradation isonicotinic acid, other antitubercular components such as ethionamide and ethambutol hydrochloride which are present in its formulations. The molar ratio and the optimum complexation condition have been studied and the orange colour formed was measured at ʎ 515nm. The method was used for the determination of isoniazid in bulk powder with mean percentage accuracy 1.00.270.84, then applied on Isocid, prepared Trecaplix and Etibi INH tablets.
A comparative study with the o66icial method showed no significant di6ference, furthermore the proposed procedure has the advantage of determination of isoniazid in the presence of other components which may be present in its formulations.