A first order derivative spectrophotometric method was developed for the simultaneous estimation of montelukast sodium (MTK) and levocetirizine dihydrochloride (LCT) in bulk and tablet dosage form, using 0.5 % w/v sodium lauryl sulfate in distilled water. The zero-crossing point in the first order derivative spectra was employed for their estimation as MTK shows measurable derivative absorbance at the zero crossing point of LCT (350.2nm), whereas LCT shows measurable derivative absorbance at the zero crossing point of MTK (211.8nm). A Good linearity was observed for both drugs over the concentration range of 3-30 μg/ml with correlation coefficient (r2) 0.999. The % recovery study found to be 98.4% to 100.5% and 99.3% to 101.25% for MTK and LCT respectively. The % RSD for precision was found to be less than 2 %; LOD was 0.993 μg/ml and 0.361 μg/ml and LOQ 3.0 μg/ml and 1.09 μg/ml respectively, for MTK and LCT. The drug content of a marketed product Telekast-L® (Lupin Lab. Ltd., India) containing 10 mg MTK and 5 mg LCT was analyzed by developed analytical method, which was found to be 98.6 % and 99.2 % for MTK and LCT respectively. Statistical analysis of the data of developed method showed that it is precise, accurate, reproducible and selective for the analysis of MTK and LCT and therefore, it can be used for simultaneous estimation of the MTK and LCT in formulations.
