Abstract. An easy, delicate, rapid and new method has been created to estimate the pharmaceutical compound Desloratadine (DES) in its bulck form and pharmaceutical forms. The method relies on the reaction of DESwith the blue dye Bromothymol blue (BTB) to form a yellow-colored product that exhibited the peak absorption occurs at a specific wavelength of 420 nm. The linear range was observed between concentrations of 5-40 µg/mL, with a molar absorptivity of 3481.184 L/mole.cm. The Sandell's sensitivity was found to be 0.0892µg/cm², and the determination coefficient (R2) was 0.9998. The limit of detection was 0.1318µg/mL, and the quantification limit was 0.3993 µg/mL. The recovery percentage values ranged from 98.7857-101.071%, with a RSD% (relative standard deviation) between 0.1546-0.6757% within a one day. The RSD% values varied between 0.0632% and 0.6859% within more day. The method was found to be accurate and sensitive, and it was successfully implemented to estimate DES in its pharmaceutical preparations using both direct and standard additions method

Abstract Received: 10/08/2023 Revised: 19/09/2023 Accepted: 30/10/2023 Published:30/09/2024 Keywords: Desloratadine DES, Montelukast sodium MON, Dual wavelengths Corresponding Author E-mail: Mobile: A new, sensitive, accurate and fast spectrophotometric method for determination of Desloratadine DES and Montelukast Sodium MON drugs was developed. The method based on the calculation of the difference in absorption at dual wavelengths. The linearity of the method was between 10-50 μg/ml for the DES drug and 5-50 μg/ml for the MON drug. The optioned recovery percentage Rec was (97.6147-103.945%) % for DES and (96.5215-103.1157) % for MON. The relative standard deviation RSD % (0.0275-0.3409) % for DES and (0.1256-0.3009) % MON. LOD was 0.1354 μg/ml for DES and 0.1604 μg/ml for MON. The LOQ was 0.4103 μg/ml for DES and 0.4861 μg/ml for MON. The Sandel's Index was 0.0917 µg/cm2 for DES and 0.1087 µg/cm2 for MON and molar absorptivity was 3387.938 L/mol.cm DES and 5595.118 L/mol.cm MON. The method was applied to the determination of DES and MON in Pharmaceutical