INDIAN DRUGS 60 (05) MAY 2023 57 STABILITY INDICATING ISOCRATIC HPLC APPROACH TO QUANTIFY MONTELUKAST AND BILASTINE MIX IN BULK AND TABLET FORMULATION Balaji Gupta V.L.N. Tiruveedhi a, b *, Venkateswara Rao Battula b , Kishore Babu Bonige b and Ramanjaneyulu V. V. Matlapudi c (Received 24 January 2021) (Accepted 24 March 2023) ABSTRACT This paper describes an novel, rapid, simple, meticulous and unerring “stability indicating HPLC meth- od” for the assessment of montelukast (MTT) and bilastine (BLE) mix in existence of their degradation products in tablet formulation. Zorbax column XDB-C18 was utilized to separate and analyse MTT and BLE mix. The isocratic mode elution of BLE and MTT mix was made with 0.1M disodium hydrogen phos- phate buffer of pH 5.8 (55 % volume ratio) and methanol (45% volume ratio) at 1.0 mL min -1 flow stream. Strong linearity was recorded within the 2.5 - 20 µg mL -1 and 5 - 40 µg mL -1 concentration ranges, with coefficient determination values of 0.9994 and 0.9997, respectively, for MTT and BLE. The recovery percentiles of MTT and BLE were 99.593 % and 99.349 %, respectively. The precision displayed val- ues less than 0.520 % for MTT and less than 0.745 % for BLE. The robustness too was shown in the chromatographic settings by minor variations. The specificity besides stability representing feature was evidenced since the degradation products arisen in stress situations did not interlope in the determina- tion of MTT and BLE mix. Thus, this procedure can be applied for quality regulation analysis of BLE and MTT mix in formulations of tablets. Keywords: Montelukast, Bilastine, Allergy treatment, Stability, HPLC, Analysis INTRODUCTION To enhance the therapeutic impact against diseases, commercial pharmaceutical formulations comprising more than one active components in pharmaceuticals including a constant matrix are used 1,2 . For the industrial production of medications, the evaluation of drug combinations seems to be very essential. We therefore need versatile, flexible and low-cost methods to achieve strongly precise as well as accurate results. Montelukast (MTT) is a potent antagonist of the receptor for cysteinyl leukotriene and possess bronchodilating and anti-inflammatory properties 3 . MTT inhibits the cysteinyl leukotriene one receptor competitively and selectively, blocking the inflammatory facilitator leukotriene D4 from binding, which results in the suppression of inflammatory effects facilitated by leukotriene. MTT is before exercising to reduce bronchospasm during exercise, to alleviate sneezing, runny/ stuffy/itchy nose while allergic rhinitis a Department of Basic Science, Vishnu Institute of Technology (A), Bhimavaram-534 201, Andhra Pradesh, India b Department of Engineering Chemistry, Andhra University, Visakhapatnam-530 003, Andhra Pradesh, India c Department of Chemistry, K G R L College (A), Bhimavaram-534 201, Andhra Pradesh, India *For Correspondence: E-mail: tvlbalaji79@gmail.com https://doi.org/10.53879/id.60.05.12856 hay fever and also to manage and stop wheezing and tightness of breath triggered by asthma 4,5 . Bilastine (BLE) is an effective antihistamine that has antiallergic effects and is highly specific for the histamine H1 receptor 6-9 . Mast cells go through degranulation during an allergic reaction, which activates histamine as well as other substances. Due to its ability to bind to and block histamine H1 receptor stimulation, BLE reduces the occurrence of allergic symptoms. The formulation of MTT and BLE mix was used for allergic seasonal rhinoconjunctivitis and mild to severe asthma as an additive treatment 10 . The MTT and BLE mix was available as tablet dose formulation. The atom arrangements of MTT and BLE are provided in Fig. 1. So far one UV spectrophotometry-based method to quantify MTT and BLE mix in tablets was described by Raj et al 11 . BLE and MTT quantification in the Raj et al. method was performed by gauging absorption at 214 nm (BLE’s λ max value) and 281 nm (MTT’s λ max value), respectively in methanol. The current strategies of the International Harmonization Conference include the development, on