Thermal stability and nonisothermal kinetics of Folnak® degradation process

Abstract

Aim: The purpose of this article is to investigate the thermal stability and nonisothermal kinetics of Folnak® drug degradation process using different thermoanalytical techniques. Methods: The nonisothermal degradation of Folnak® powder samples was investigated by simultaneous thermogravimetry–differential thermal analysis, in the temperature range from ambient to 810°C. Results: It was found that the degradation proceeds through five reaction stages, which include the dehydration, the melting process of excipients, the decomposition of folic acid, corn starch, and saccharose. The presence of compounds such as excipients increases the thermal stability of the drug and some kind of solid–solid and/or solid–gas interaction occurs. Conclusion: It was concluded that the main degradation stage of Folnak® sample represents the decomposition of folic acid. It was established that the folic acid decomposition cannot be explained by simple reaction order model (n = 1) but with the complex reaction mechanism that includes higher reaction orders (n > 1). The isothermal predictions of the folic acid decomposition at four different temperatures (T_iso = 180°C, 200°C, 220°C, and 260°C) were established. It was concluded that the shapes of conversion curves at lower temperatures (180–200°C) were similar, whereas they became more complex with further temperature increase because of the complexity of the decomposition reaction.

Keywords:

• Drug interactions
• excipients
• kinetics
• nonlinear regression
• stability
• thermogravimetric analysis