Inhibition of Crystal Nucleation and Growth in Aqueous Drug Solutions: Impact of Different Polymers on the Supersaturation Profiles of Amorphous Drugs—The Case of Alpha-Mangostin

Abstract

The polymer used in supersaturated solutions plays a critical role in maintaining supersaturation levels of amorphous drugs. The prevention of drug crystallization in the supersaturated solutions by adding polymers depends on their ability to inhibit nucleation and crystal growth of drugs. This showed that understanding the mechanism of nucleation inhibition by polymers is necessary to develop the drug formulation in supersaturated solutions. Therefore, this study aims to evaluate the impact of water-soluble polymers on the supersaturation behavior of drugs and elucidate the mechanism of maintaining the supersaturation levels in an aqueous solution. It was carried out using alpha-mangostin (AM) as a model of the poorly water-soluble drug, while hypromellose (HPMC), polyvinylpyrrolidone (PVP), and eudragit were used as polymers. Their ability to inhibit the nucleation and crystal growth of AM was also evaluated. The supersaturation profiles of AM were measured in biorelevant dissolution media, while the crystal growth rate of AM was evaluated from the decrease in dissolved drug concentration by determining the induction time for AM nucleation. The interaction of AM with each polymer was evaluated and predicted by FT-IR, NMR measurement, and an in silico study, respectively. Based on observation, the PVP effectively maintained AM in a supersaturated state for the long term while eudragit conserved for 15 min. Meanwhile, an inhibitory effect of HPMC on the AM crystal nucleation was not observed. It was also discovered that the effectiveness of the various polymers depends on the interaction between the polymer and the drug. FT-IR and in silico studies demonstrated that the interaction of PVP-AM had the best polymer compared to eudragit and HPMC. NMR analysis suggested that the interaction between the methyl group from PVP with the carbonyl group of AM occurred in the PVP solution. The viscosity measurement revealed that the inhibition of nucleation and crystal growth of AM was not caused by increasing the viscosity. These results indicated that polymer–AM interactions could contribute to the crystallization inhibition and maintenance of AM in a supersaturated state. Therefore, an investigation of the mechanism of drug nucleation inhibition by polymers is recommended in the selection of crystallization inhibitors and a planned strategy to develop supersaturated formulations of drugs.