Selection of appropriate dapsone and poly(1-vinylpyrrolidone-co-vinyl acetate) ratios for the preparation of amorphous solid dispersions

Drug-polymer miscibility is a critical requirement for the efficient design and development of amorphous solid dispersions. The objective of the current study was to determine the miscibility between dapsone (DAP) and poly(1-vinylpyrrolidone-co-vinyl acetate) (PVP-VA) through theoretical and experimental approaches, including the use of a thermodynamic phase diagram and Gibbs free energy of mixing. In the theoretical study, the difference in the solubility parameter between the DAP and PVP-VA was 2.74, the interaction parameter was 0.50, and the distance between the drug and polymer in the Bagley plot was 2.60. Hence, all these theoretical parameters favour the miscibility between DAP and PVP-VA. Melting point depression study (through thermal analysis) and Flory-Huggins theory were utilized for the practical determination of drug-polymer miscibility, where the interaction parameter was positive, suggesting limited miscibility. The obtained thermodynamic phase diagram and Gibbs free energy of mixing plot can provide an indication for the selection of appropriate drug-polymer ratios in stable and metastable zones and the optimum processing temperature required for the preparation of amorphous solid dispersions.