Thermal investigation of relaxations of interacting and non-interacting amorphous solid dispersions

Abstract

In the present research, thermal investigation of amorphous solid dispersions (ASDs) was performed in order to compare their relaxation transitions. Two different active pharmaceutical ingredients (APIs), namely naproxen (NAP) and spironolactone (SPIR), were used as model drugs and combined with polyvinylpyrrolidone vinyl acetate (PVPVA64) copolymer to form stable ASDs. The reason for the API selection was their different interacting potentials based on the presence (in the case of NAP) and the lack of H-bond donor group (in the case of SPIR). Determination of both Tg and sub-Tg transitions suggested that ASDs containing NAP and PVPVA64 are ‘interacting’ systems with respect to the H-bonding. Besides, temperature-dependent Raman spectroscopic experiments confirmed that the naphthalene ring of the NAP has a significant role in the sub-Tg relaxations. In contrast, SPIR-PVPVA64 systems proved to be ‘non-interacting’ ASDs according to the MDSC, TSDC, and Raman measurements. This study highlights that the combination of the results of different thermoanalytical investigations with spectroscopic methods helps to understand the molecular background of the relaxations in ASDs and thus contributes to the conscious design of stable amorphous pharmaceuticals in the early stage of development.