Thermooxidation of Four Sartans: Kinetic Analysis Based on Thermo-Gravimetric Data

Angiotensin II receptor antagonists are tetrazole derivatives used in the treatment of high blood pressure, and are also indicated for the treatment of heart failure (NYHA class II-IV). They are used alone or in combination with other classes of antihypertensives or diuretics for the effective management of high blood pressure. In this study, we aim to evaluate the thermal stability and degradation kinetics for the principal compounds used in therapy from this class, namely telmisartan, valsartan, olmesartan medoxomil, and losartan potassium. To obtain the thermoanalytical data for the kinetic investigations, the TG and DTG curves were registered at five different heating rates (beta = 2, 4, 6, 8, and 10 degrees C min-1). The kinetic methods used were a preliminary ASTM E698 method and two isoconversional methods: Flynn-Wall-Ozawa and Friedman. For each molecule, the results showed complex decomposition processes consisting of complex reaction sequences.