Thermal behavior of verapamil in pure and in solid dosage forms

Verapamil is a phenyl-alchil-amine type pharmaceutical largely used as a specific calcium antagonist. Knowledge of drug-excipient compatibility represents an important phase in development of different dosage forms. Hyphenated techniques are versatile for obtaining such necessary information’s. The TG/DTG/DTA curves were obtained in air at different heating rates and in nitrogen. The IR spectra of pure compound and its char at 400 °C (by U-ATR technique) and the IR identification of Evolved Gasses allowed some discussions on the thermally induced events. In the solid dosage forms verapamil was mixed with talc, magnesium stearate, starch, and cellulose, and the corresponding thermoanalytical curves were compared with that one of pure I. No physical or chemical interactions were observed till 250 °C. A kinetic analysis was performed for TG step of verapamil between 250 and 350 °C. The data at four heating rates (7, 10, 12, 15 °C min⁻¹) were processed on a strategy using at last three different kinetic methods. For these, the NPK method seems to be less speculative, allowing an objective determination of the kinetic parameters.