Purpose
The aim of this study was to perform a thermodynamic and kinetic investigation on the crucial factors affecting the cocrystallization between adefovir dipivoxil (AD) and saccharin (SAC).
Methods
Phase solubility diagrams and ternary phase diagrams were constructed based on the solubility data of AD, SAC and their cocrystals in ethanol, isopropanol and ethyl acetate at different temperatures. The conductimetric method was used to determine the induction time. A quantitative and intuitive technique modified from dissolution testing was employed to investigate the cocrystallization kinetics.
Results
AD-SAC cocrystals exhibited different crystal habits but only one cocrystal polymorph was confirmed. The effects of several crucial factors, including the input amounts of two components, AD/SAC ratio, solvent and temperature, on the crystallization of single-component alone, cocrystal formation, cocrystal stability, supersaturation, nucleation, crystal growth and cocrystal yield were determined. Thermodynamic and kinetic parameters provided the rationale for this spontaneous cocrystallization system without the need of solvent evaporation and temperature change.
Conclusions
This systemic investigation enriched the present understanding of thermodynamics and kinetics of cocrystals and built the groundwork for AD-SAC cocrystal scale-up.