IMI - oral biopharmaceutics tools project - evaluation of bottom-up PBPK prediction success part 1: Characterisation of the OrBiTo database of compounds.

Predicting oral bioavailability (Foral) is of importance for estimating systemic exposure of orally administered drugs. Physiologically-based pharmacokinetic (PBPK) modelling and simulation have been applied extensively in biopharmaceutics recently. The Oral Biopharmaceutical Tools (OrBiTo) project (Innovative Medicines Initiative) aims to develop and improve upon biopharmaceutical tools, including PBPK absorption models. A large-scale evaluation of PBPK models may be considered the first step. Here we characterise the OrBiTo active pharmaceutical ingredient (API) database for use in a large-scale simulation study. The OrBiTo database comprised 83 APIs and 1475 study arms. The database displayed a median logP of 3.60 (2.40-4.58), human blood-to-plasma ratio of 0.62 (0.57-0.71), and fraction unbound in plasma of 0.05 (0.01-0.17). The database mainly consisted of basic compounds (48.19%) and Biopharmaceutics Classification System class II compounds (55.81%). Median human intravenous clearance was 16.9L/h (interquartile range: 11.6-43.6L/h; n=23), volume of distribution was 80.8L (54.5-239L; n=23). The majority of oral formulations were immediate release (IR: 87.6%). Human Foral displayed a median of 0.415 (0.203-0.724; n=22) for IR formulations. The OrBiTo database was found to be largely representative of previously published datasets. 43 of the APIs were found to satisfy the minimum inclusion criteria for the simulation exercise, and many of these have significant gaps of other key parameters, which could potentially impact the interpretability of the simulation outcome. However, the OrBiTo simulation exercise represents a unique opportunity to perform a large-scale evaluation of the PBPK approach to predicting oral biopharmaceutics.

Biopharmaceutical classification of poorly soluble drugs with respect to "enabling formulations".

The large number of drug candidates with poor dissolution characteristics seen in the past decade, has fostered interest in so-called "enabling formulations", i.e., formulations which shall make such drugs bio-available. Development of enabling formulations is currently being guided by the following (simplified) hypothesis: If a poorly soluble drug (BCS class II drug) can be transferred into a solubilized state, one can achieve an absorption profile close to that of a soluble drug (BCS class I drug). Thus, formulation development typically endeavors to achieve the most robust solubility enhancement. Here we critically review both common in vitro approaches and experimental data available in literature pertaining to the solubility and permeability of poorly soluble drugs from enabling formulations, and discuss their interplay. Recent in vitro data indicate, that commonly employed surfactants as well as endogenous surfactants present in the intestine, although enhancing drug solubility, mostly hamper drug permeation. Mechanistic studies demonstrate a direct correlation between passive transcellular diffusion and the concentration of molecularly dissolved drug. The latter may be reduced due to partitioning into micelles or other solubilizing carriers, but enhanced in supersaturating formulations. We conclude thus that biopharmaceutical assessment approaches that rely on the amount of molecularly dissolved drug should guide us towards successful enabling formulations.