Physiologically Based Biopharmaceutics Modeling of Food Effect for Basmisanil: A Retrospective Case Study of the Utility for Formulation Bridging

Basmisanil, is a lipophilic drug substance, exhibiting poor solubility and good permeability (BCS class 2). A validated physiologically based biopharmaceutics model (PBBM) has been previously described for tablets dosed in the fed state. The PBBM captured the less than proportional increases in exposure at higher doses well and indicated that absorption was dissolution rate-limited below 200 mg while solubility was limiting for higher doses. In this study, a model for dosing in the fasted state is described and is verified for simulation of the food effect where exposures were ~1.5 fold higher when a 660 mg tablet was given with food. The model is then applied to simulate the food effect for a granules formulation given at a lower dose (120 mg). The food effect at the lower dose was reasonably simulated with a ratio of simulated/observed food effect of 1.35 for Cmax and 0.83 for AUC. Sensitivity analysis was carried out for uncertain model parameters to confirm that the model could predict the magnitude of the positive food effect with moderate to high confidence. This study suggests that a verified PBBM can provide a useful alternative to a repeat food effect study when formulation changes are minor. However, there is need for further evaluation of the approach and a definition of what formulation changes are minor in this context. In addition, this work highlights some uncertainties in the handling of solubility in PBBM, in particular around temperature dependency of solubility and the parameterization of bile salt solubilization using measurements in biorelevant media.

Processing Impact on Performance of Solid Dispersions

The development of a weakly basic compound is often challenging due to changes in pH that the drug experiences throughout the gastrointestinal tract. As the drug transitions from the low pH of the stomach to the higher pH of the small intestine, drug solubility decreases. A stomach with a higher pH, caused by food or achlorhydric conditions brought about by certain medications, decreases even the initial solubility. This decreased drug solubility is reflected in lower in vivo exposures. In many cases, a solubility-enabling approach is needed to counteract the effect of gastrointestinal pH changes. Solid dispersions of amorphous drug in a polymer matrix have been demonstrated to be an effective tool to enhance bioavailability, with the potential to mitigate the food and achlorhydric effects frequently observed with conventional formulations. Because solid dispersions are in a metastable state, they are particularly sensitive to processing routes that may control particle attributes, stability, drug release profile, and bioperformance. A better understanding of the impacts of processing routes on the solid dispersion properties will not only enhance our ability to control the product properties, but also lower development risks. In this study, a weakly basic compound with greatly reduced solubility in higher pHs was incorporated into a solid dispersion via both spray drying and hot melt extrusion. The properties of the solid dispersion via these two processing routes were compared, and the impact on dissolution behavior and in vivo performance of the dispersions was investigated.

Characterising Drug Release from Immediate-Release Formulations of a Poorly Soluble Compound, Basmisanil, Through Absorption Modelling and Dissolution Testing

The study aimed to characterise the mechanism of release and absorption of Basmisanil, a biopharmaceutics classification system (BCS) class 2 compound, from immediate-release formulations via mechanistic absorption modelling, dissolution testing, and Raman imaging. An oral absorption model was developed in GastroPlus® and verified with single-dose pharmacokinetic data in humans. The properties and drug release behaviour of different oral Basmisanil formulations were characterised via biorelevant dissolution and Raman imaging studies. Finally, an in vitro-in vivo correlation (IVIVC) model was developed using conventional and mechanistic deconvolution methods for comparison. The GastroPlus model accurately simulated oral Basmisanil exposure from tablets and granules formulations containing micronized drug. Absorption of oral doses below 200 mg was mostly dissolution rate-limited and thus particularly sensitive to formulation properties. Indeed, reduced exposure was observed for a 120-mg film-coated tablet and the slower dissolution rate measured in biorelevant media was attributed to differences in drug load. This hypothesis was confirmed when Raman imaging showed that the percolation threshold was exceeded in this formulation. This biorelevant dissolution method clearly differentiated between the formulations and was used to develop a robust IVIVC model. The study demonstrates the applicability and impact of mechanistic absorption modelling and biopharmaceutical in vitro tools for rational drug development.