Effects of Molecular Interactions on Miscibility and Mobility of Ibuprofen in Amorphous Solid Dispersions With Various Polymers.

Hydrogen bonds (HBs) in amorphous solid dispersions may influence physical stability through effects on both drug miscibility and mobility. Amorphous solid dispersions containing the HB-donor ibuprofen (IBP) alone or with one of four model polymers (poly(vinyl pyrrolidone) [PVP], poly(vinyl pyrrolidone/vinyl acetate) [PVP/VA], poly(vinyl acetate) [PVA], or polystyrene [PST]) were monitored by molecular dynamics simulation. HB distributions and contributions of electrostatic, van der Waals, and internal interactions to miscibility and mobility were analyzed versus drug concentration. The probability of IBP-IBP HBs decreases markedly (0.6→0.0) with dilution (100→10% drug) in PVP due to IBP-PVP HBs while dilution in the nonpolar PST has a more modest effect on IBP-IBP HB probability (0.6→0.3). Concentration-dependent Flory-Huggins interaction parameters (χ) were determined to assess drug-polymer miscibility. χ values were -0.9 to -1.8 with a plateau near 50% w/w PVP, whereas χ fluctuated near zero (-0.1 to 0.3), suggesting that IBP is more soluble in PVP than in PST. χ values in polymers varying in pyrrolidone/acetate composition were in the order PVP (most favorable) > PVP/VA > PVA (least favorable). Decreased local mobility of IBP measured by the atomic fluctuation correlates with more IBP-PVP HBs with increasing PVP content. The opposite trend in IBP-PST may arise from IBP-IBP HB disruption on dilution.