Ligand substitution kinetic assay of antitubercular drug isoniazid in pure and pharmaceutical formulations

• A sensitive kinetic assay for anti-tubercular drug isoniazid was developed.
• A method using ligand substitution reaction and spectrophotometric monitoring was validated to determine isoniazid.
• The kinetic assay of pyridine-4-carboxylic acid hydrazide compared well with the official analytical method.
• Anti-tubercular drug isoniazid was analyzed in pure and pharmaceutical formulations.
• Study showed a method for rapid determination of anti-tubercular drug isoniazid.
• The method was used for the monitoring of isoniazid in drug formulations.

The interaction of isoniazid (INH) with [Fe(CN)5(H2O)]3 − in aqueous solution at pH 3.8 was found to give intensely golden yellow color product, [Fe(CN)5(INH)]3 −, which strongly absorbs at 435 nm without any interference with the reactants. The effect of several reaction variables on the rate of the complex [Fe(CN)5(INH)]3 − formation was studied and optimized. Thus a simple, rapid, selective and economical analytical method based on the ligand substitution (LS) kinetic assay of INH in pure as well as in dosage forms involving the reaction between [Fe(CN)5(H2O)]3 − and INH has been reported. The isoniazid can be determined in the range 1.37–13.71 μg mL− 1 by measuring the initial rate of the complex formed during the course of the reaction at 435 nm. The detection limit has been established to be 0.15 μg mL− 1 of INH. Recovery experiment was carried out to ensure the accuracy and the precision in the quantification of INH. The proposed method has successfully been applied for the analysis of INH in pure samples and a number of its pharmaceutical formulations with excellent accuracy and precision while the results were compared with those obtained by the official analytical method, and were in well agreement. The common excipients used as additives in pharmaceuticals do not interfere in the proposed method. It was possible to do 20 analyses per hour.