Congruent release of drug and polymer from amorphous solid dispersions: insights into the role of drug-polymer hydrogen bonding, surface crystallization and glass transition

Drug loading is an important parameter known to impact the release rate of a poorly soluble drug from an amorphous solid dispersion (ASD). Recent studies have shown that small increases in drug loading can dramatically reduce the drug release rate from ASDs prepared with poly (vinylpyrrolidone-co-vinyl acetate) (PVPVA). However, the link between drug physicochemical properties and the drug loading where release is abruptly compromised is not well understood.

This study probes the role of three different factors on the relative dissolution rates of drug and polymer from PVPVA-based ASDs as a function of drug loading: 1) the impact of drug-polymer hydrogen bonding interactions on the initial dissolution rate of ASDs, investigated using two structural analogues, indomethacin (IND) and indomethacin methyl ester (INDester), 2) the influence of surface drug crystallization, observed for INDester ASDs, and 3) by changing temperature, the impact of ‘wet’ glass transition temperature (Tg). Scanning electron microscopy (SEM), with or without energy dispersive X-ray (EDX) analysis, Fourier transform infrared spectroscopy (FTIR) and powder X-ray diffraction (PXRD) were utilized to study the solid-state phase behavior and/or drug enrichment on the partially dissolved ASD tablet surfaces. Nanoparticle tracking analysis (NTA) was utilized to study the solution-state phase behavior.

It was found that, contrary to expectations, ASDs with drug-polymer hydrogen bonding exhibited poorer initial release at moderate drug loadings (15-25%) as compared to the non-hydrogen bonding analog ASDs. In line with expectations, surface crystallization led to deterioration of dissolution performance. Lastly, Tg was also found to play a role in the observed dissolution behavior as a function of drug loading. These findings shed light on mechanisms governing ASD dissolution performance and will aid in the development of optimized ASD formulations with enhanced dissolution performance.

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Article Information: Sugandha Saboo, Umesh S. Kestur, Daniel P. Flaherty, Lynne S. Taylor; Molecular Pharmaceutics, 2020.