Diode array detection and derivative spectroscopic methods for stability study of Oxprenolol and Cyclopenthiazide in liquids

Today, many single-pill combinations (SPC) exist and are used as a promising choice in hypertension treatment. However, this trend made more of a challenge to analysts in Pharmaceutical Quality Control Laboratories. In this work, three sensitive and selective analytical methods were proposed for simultaneous determination of two anti-hypertension drugs; Oxprenolol (OXP) and Cyclopenthiazide (CYPZ) in bulk powder and in laboratory prepared tablets "LPTs". Two of them were simple spectrophotometric methods (derivative and derivative ratio) and the third was HPLC-DAD method. For the spectrophotometric methods, the major problem encountered during analysis was attributed to the extensive spectral overlap and the challenging ratio of both drugs in their dosage form, CYPZ:OXP (0.2:100). The derivative (D) method was based on using the first derivative (D-1) and second derivative (D-2) spectra for the quantitative analysis of CYPZ at 335.5 nm and OXP at 280.5 nm, respectively. While for the derivative ratio method ((DR)-D-1), OXP was determined at 285.5 nm and CYPZ at 335.5 nm. The HPLC method was based on the separation of both drugs on a C-18 column with a mobile phase containing acetonitrile and 50 mM phosphate buffer of pH 3.5 (50:50). In order to quantify OXP and CYPZ accurately and maximize the assay sensitivity; the DAD was set at 224 nm. Optimization of chromatographic conditions was done at which OXP eluted at 4.34 min and CYPZ at 6.73 min with optimum sharpness and peak symmetry. The study of forced degradation of both drugs was done under various conditions including; hydrolysis (acid, alkaline and neutral), oxidation, dry heat and photo-decomposition. The proposed method could separate each drug peak from those of the different forced degradation product peaks and the purity of the drugs peaks was confirmed using the photo-diode array detector. The data obtained by spectrophotometric and HPLC methods were statistically comparable by ANOVA test. No significant difference was recorded between the mean percent levels determined by the proposed methods. (C) 2017 Elsevier B.V. All rights reserved.