Exploiting common ion addition to accelerate zolpidem hemitartrate release from Eudragit EPO extrudates

The current study aimed at optimizing a previously developed non-clinical formulation for use in zolpidem deprescribing. The formulation under investigation consists of extruded zolpidem hemitartrate (30% w/w) and Eudragit EPO (70% w/w) mixtures which display unsatisfactory dissolution behavior. Both milled extrudates and physical mixtures were compressed to produce tablets with identical target weight and solid fraction. First, the susceptibility of zolpidem hemitartrate towards heat and shear degradation was identified utilizing thermal and HPLC-DAD analysis. The drug salt proved prone to thermally induced disproportionation. Moreover, the impurity content increased after applying hot melt extrusion although ICH guidelines were still attained. Secondly, extrudates and physical mixtures were subjected to FTIR analysis. As a result, interaction and protonation of the dimethyl aminoethyl group from Eudragit EPO resulting from zolpidem disproportionation was elucidated. As such, the formulations' slow dissolution kinetics in comparison to formulations containing non-ionizable polymers (e.g. Kollidon 12PF and Kollidon VA64) is explained. Finally, addition of tartaric acid, a microenvironmental pH modulator and common ion, proved a successful method to increase dissolution kinetics. The amount of drug released after 15 min increased drastically from 10 to 40% upon the addition of 5% tartaric acid. Immediate release behavior (80% within 15 min) was however not yet attained.