Simultaneous Spectrophotometric & Spectrofluorimetric Assay of Silodosin & Solifenacin in their Co-formulated Binary Mixture

Objectives: New pharmaceutical combinations are routinely developed and marketed to improve treatment of different conditions, increase patient compliance and simplify the medication regimen. However, such case necessities the development of analytical procedures to assay these new mixtures in different matrices. This is the case for Silodosin (SI) & Solifenacin (SO) new combination marketed to treat patients’ stent-related symptoms and urological disorders. The simplest and greenest known analytical methods are the spectrophotometric and spectrofluorimetric ones. Thus, these two techniques were chosen to resolve this new binary mixture and assay the drugs in their bulk and dosage form to be routine methods for their analysis. Methods: Method I relies on applying third derivative treatment on the two drugs’ absorption spectra to measure SI at 280 nm and SO at 222 nm. Method II is direct spectofluorimetric measurement of SI at its λem of 445 nm and SO at λem of 276 nm. Results: The methods are validated according to “ICH guidelines” to be the first valid reported methods for this new mixture. Linearity was achieved at 6.50-19.20 & 2.50-10.00 µg/mL for SI and SO, respectively, in case of method I and at 0.30-12.80 & 1.00-22.00 µg/mL for SI and SO, respectively, in case of method II. The two proposed methods showed high sensitivity, accuracy and selectivity for each drug. Conclusion: The methods in this study were applied successfully to determine SI and SO in their bulk and laboratory prepared tablets with acceptable validation parameters.