Physicochemical characterization of nicergoline and cabergoline in its amorphous state

Formulation of poorly water-soluble crystalline drugs into their more soluble amorphous form is a common approach for improving their bioavailability. In this study, the amorphous forms of nicergoline (NIC) and cabergoline (CAB) were obtained by different methods (melting and precipitation under solvent evaporation). The physicochemical characteristics of the samples were determined by HPLC, differential scanning calorimetry (DSC), thermogravimetry, and X-ray powder diffractometry. The physical stability of the amorphous forms was investigated by DSC by considering how the onset temperature and the enthalpy content at the glass transition vary with aging time and temperature. Using the Kohlrausch-Williams-Watts equation on the data obtained from the experiments, the "mean molecular relaxation time constant" (τ) was estimated. This parameter was used to understand the stability of NIC and CAB in their glassy state at different temperatures, and results showed that their stability is adequate to enable the formulation of these drugs into solid dosage forms. © 2011 Akadémiai Kiadó, Budapest, Hungary.