A Rapid, Sensitive, and High-throughput Method for the Simultaneous Determination of Antihypertensive Drug Combinations in Dog Plasma by UHPLC-MS/MS: The Assessment of Predicable Bioequivalence of In-vitro Dissolution Condition

Background: Essential hypertension is a common clinical disease and a risk factor for cardiovascular and cerebrovascular diseases. Olmesartan medoxomil, amlodipine, and hydrochlorothiazide are commonly used antihypertensive drugs. The aim of this study was to establish a robust UPLC-MS/MS method for the simultaneous determination of olmesartan medoxomil, amlodipine, and hydrochlorothiazide in dog plasma. At the same time, the in vivo and in vitro release studies were conducted, and a preliminary in vitro-in vivo correlation (IVIVC) evaluation was performed. Methods: The bioequivalence experiment was conducted with a double-crossed design. Three major components were extracted and analyzed by UHPLC-MS/MS. With the MRM scan, olmesartan and amlodipine were quantified by fragment conversion (m/z 447.10→190.10) and (m/z 408.95→294.00) under positive ESI mode, while hydrochlorothiazide was quantified with fragment conversion (m/z 295.90→268.90) under negative ESI mode. The in vitro release studies were performed using a USP paddle, and the dissolution medium was chosen from pH 6.0 to pH 6.8 according to the BCS classification of compounds. The IVIVC was calculated using the Wagner-Nelson equation. Results: The linear ranges of olmesartan, amlodipine, and hydrochlorothiazide in the plasma were 5.0-2500, 0.1-50, and 3.0-1500 ng/mL, respectively. All accuracies were within 3.8% of the target values, and the findings revealed that intra-day and inter-day accuracies were less than 12.1%. Moreover, the recoveries exceeded 88.3%, the matrix effect tests were positive, and the stability tests were positive. With the establishment of correlation, the distinguishable dissolution condition (pH 6.8) was selected as the predictable condition. Conclusion: The established method was suitable for the preclinical pharmacokinetic study of tripartite drugs with strong specificity and high sensitivity. Through the evaluation of IVIVC, the connection between in vivo and in vitro drug testing was initially established.