Formulating amorphous solid dispersions: Impact of inorganic salts on drug release from tablets containing Itraconazole-HPMC extrudate.

Amorphous solid dispersions (ASD) are increasingly used to improve the oral bioavailability of poorly water-soluble compounds. However, hydrophilic polymers in ASD have high water binding properties and, upon water contact, they often form a gel on the surface of the tablet impacting the rate and extent of drug release. Most inorganic salts decrease water solubility of organic solute, changing gel properties of hydrophilic polymer. In this study, the effect of inorganic salts on drug release from a tablet formulation containing an Itraconazole (ITZ)-HPMC extrudate was investigated. The cloud point of a 1% HPMC solution with and without inorganic salts (KCl, KH2PO4, KHCO3 and KI) was determined in order to classify the salts according to their salting-out or salting-in effect. A kosmotropic effect on HPMC was observed for KCl, KH2PO4 and KHCO3, whereas KI exhibited a chaotropic effect. In order to prove the effect of these salts on drug release, tablets containing 66% of ITZ-HPMC extrudate (20:80 w/w%), 4% croscarmellose sodium, 30% microcrystalline cellulose and different types and amounts of KHCO3, KH2PO4, KCl, and KI were compressed (same solid fraction of 0.83 - 0.85). Tablets without salts showed a slow release and low peak concentrations during dissolution in simulated gastric fluids. By adding the kosmotropic salts to the tablets, the rate and extent of drug release were increased, whereas the chaotropic anion iodide had no effect. The effect was pronounced even with the addition of as little as 2% of inorganic salts and tended to increase with increasing amount of salt in the formulation. Tablets without salt stored under either dry or humid conditions exhibited a large difference in dissolution profiles, whereas little variation was observed for tablets with kosmotropic salts. In conclusion, the effect of inorganic salt was mechanistically clarified on ASD containing commonly used HPMC. This approach can be beneficial to successfully develop robust formulations containing ASD.