ESTIMATION OF DEXTROMETHORPHAN HYDROBROMIDE AND QUINIDINE SULPHATE IN THEIR COMBINED DOSAGE FORMS USING SIMULTANEOUS EQUATION METHOD

A simple, accurate, precise and specific simultaneous equation method has been developed and validated for simultaneous estimation of dextromethorphan hydrobromide and quinidine sulphate in their combined dosage form approved by USFDA (brand name Nuedexta capsules) in October 2010. Absorbances were measured in 0.5 M methanolic HCl at 226 nm (?max of dextromethorphan) and at 253 nm (?max of quinidine). Beers law was followed within the range of 5-40 mcg/mcL for dextromethorphan with coefficient of correlation 0.9997 and 2-18 mcg/mcL and for quinidine with coefficient of correlation 0.998. LOD and LOQ for dextromethorphan was found to be 1.36 mcg/mL and 4.55 mcg/mL while for quinidine it was 0.34 mcg/mL and 1.14 mcg/mL. Results of accuracy, precision and specificity were well within acceptance criteria which indicate that the method has excellent scope for simultaneous estimation of dextromethorphan and quinidine in combined dosage form.