A Stability-Indicating High Performance Liquid Chromatographic Assay for the Simultaneous Determination of Pyridoxine, Ethionamide, and Moxifloxacin in Fixed Dose Combination Tablets

Stability indicating reversed phase HPLC method was developed and validated for the simultaneous quantitation of antitubercular drugs, ethionamide (ETH), and moxifloxacin (MOX) with commonly coprescribed vitamin, pyridoxine (PYR) in tablet dosage form. The method was found rapid, precise and accurate. The separation was performed in Hibar 150-4.6, Purospher STAR, RP-18e (5？μm) column, using mobile phase A (0.03？M sodium citrate adjusted to pH 5 with glacial acetic acid) and mobile phase B (100% methanol), ran at variable proportions at flow rate of 1.0？mL/min. The detection was carried out at 320？nm. The method was observed linearly in the range of 2.5–17.5？μg/mL for PYR, 25–175？μg/mL for ETH, and 40–280？μg/mL for MOX with respective limits of detection/quantitation of 0.125？μg/mL/1.28？μg/mL, 0.25？μg/mL/2.56？μg/mL, and 0.35？μg/mL/3.65？μg/mL. The drugs were also subjected to oxidative, hydrolytic, photolytic, and thermal degradation; the degradation products showed interference with the detection of PYR, ETH, and MOX. The proposed method was observed to be effective to quantitate MOX (400？mg), ETH (250？mg), and PYR (25？mg) in fixed dose combination tablet formulation. 1. Introduction Moxifloxacin is a fluoroquinolones antibacterial agent having potent activity against M. tuberculosis, including MDR strains in 400？mg daily dose. Ethionamide is a traditional second line therapy drug for the treatment of tuberculosis in 250–1000？mg daily dose to avoid rapid development of resistance [1–6]. In order to reduce the problems associated with peripheral neuropathy caused by daily high dose of ethionamide therapy, pyridoxine dose ranging from 2.5 to 25？mg is usually added typically along with the above mentioned therapies [7]. In present work, a fixed dose combination of moxifloxacin 400？mg, ethionamide 250？mg, and pyridoxine 25？mg was designed to reduce the duration and neurologic side effects associated with antitubercular therapy (Figure 1) [8, 9]. Figure 1: Chemical structures of (1) pyridoxine, (2) ethionamide, (3) moxifloxacin, and (4) ciprofloxacin. The literature [8–21] and official monographs of BP [16] and USP [17] present spectrophotometric and HPLC methods for the individual quantitative determination of PYR, ETH, and MOX from the bulk and dosage forms. Therefore, in this study, a rapid, precise, and accurate reversed phase HPLC method was developed and validated for the simultaneous estimation of these drugs. But there is no stability indicating HPLC method available for the determination of these drugs. A drug and drug product is regarded as stable