Thermal analysis study of amlodipine as pure compound and in binary mixture

Amlodipine is a very used selective calcium antagonist. The evaluation of thermal stability is crucial for the formulation setting of a solid dosage form. By heating in air under non-isothermal conditions, amlodipine presents two characteristic steps. More details were obtained using IR spectrometric data of the pure compound of the char, respectively, of the evolved gases at those temperatures. Data on a possible interaction between amlodipine and some excipients used in solid dosage forms were obtained by comparison of TG/DTG/DTA curves of amlodipine and of its mixtures with talc (considered thermally inert), magnesium stearate, starch and cellulose. No thermally induced interactions were observed. In order to obtain data for a believable Life Time Prediction a kinetic analysis was performed. The data of the first step of mass loss obtained at four heating rates (7, 10, 12, and 15 °C min⁻¹, respectively) were processed using at least three different methods. From these, the NPK method seems to be adequate because the separation between the temperature, respective the conversion dependent part of the reaction rate equation and the expression of the formal kinetic equation were obtained in a less speculative manner.