Pharmaceutical characterisation and evaluation of cocrystals: importance of in vitro dissolution conditions and type of coformer

The objectives of this study were to demonstrate the importance of experimental set-up and type of coformer for the enhanced dissolution properties of cocrystals. Carbamazepine–saccharin and carbamazepine–nicotinamide cocrystals were prepared by the sonic slurry method and characterised with SEM, DSC, XRPD and particle size analysis. Solubility and dissolution testing (closed and open system) were performed in compendial media and media with a physiologically relevant amount of surfactant. Carbamazepine cocrystals (1:1 molar ratio) did not show a difference in the equilibrium solubility compared to the carbamazepine in compendial media but a substantial difference was observed in modified media. In compendial media, a faster dissolution rate was obtained only from the carbamazepine–saccharin cocrystal, whereas in modified media both cocrystals had a substantial higher dissolution compared to carbamazepine. With the selected method a clear difference in the dissolution profiles of each cocrystal is shown, driven by the characteristics of the coformer used. This study demonstrated that improved dissolution of carbamazepine from the cocrystal forms can be revealed only by appropriate selection of in vitro conditions. The characteristics of the coformer define a critical variable for dissolution of pharmaceutical cocrystals with important implications for their in vivo performance.