Bicarbonate buffer dissolution test with gentle mechanistic stress for bioequivalence prediction of enteric-coated pellet formulations.

This study aimed to develop a dissolution test that can predict the bioequivalence (BE) of enteric-coated pellet formulations. The original duloxetine hydrochloride capsule (reference formulation (RF); Cymbalta® 30 mg capsule) and four generic test formulations (two capsules (CP) and two orally disintegrating tablets (OD)) were used as model formulations. Clinical BE studies were conducted on 24-47 healthy male subjects under fasting conditions. Dissolution tests were performed using a compendial paddle method (PD) (paddle speed: 50 rpm) and a flow-through cell method (FTC) (flow rate: 4 mL/min). For a further test, cotton balls were added to the vessel to apply gentle mechanistic stress to the formulations, and paddle speed was reduced to 10 rpm (paddle with cotton ball method (PDCB)).All the dissolution tests were conducted with 0.01 M HCl (pH 2.0) for 0.5 h followed by 10 mM bicarbonate buffer solutions (pH 6.5) for 4 h. One each of the two CP and two OD showed BE with RF. PDCB was able to discriminate between BE and non-BE formulations, while this was not possible with PD and FTC. In PDCB, the cotton balls intermittently moved the pellets near the vessel bottom. PDCB is useful for predicting BE during formulation development.

Prediction of Oral Drug Absorption in Rats from In Vitro Data.

PURPOSE: In drug discovery, rats are widely used for pharmacological and toxicological studies. We previously reported that a mechanism-based oral absorption model, the gastrointestinal unified theoretical framework (GUT framework), can appropriately predict the fraction of a dose absorbed (Fa) in humans and dogs. However, there are large species differences between humans and rats. The purpose of the present study was to evaluate the predictability of the GUT framework for rat Fa. METHOD: The Fa values of 20 model drugs (a total of 39 Fa data) were predicted in a bottom-up manner. Based on the literature survey, the bile acid concentration (Cbile) and the intestinal fluid volume were set to 15 mM and 4 mL/kg, respectively, five and two times higher than in humans. LogP, pKa, molecular weight, intrinsic solubility, bile micelle partition coefficients, and Caco-2 permeability were used as input data. RESULTS: The Fa values were appropriately predicted for highly soluble drugs (absolute average fold error (AAFE) = 1.65, 18 Fa data) and poorly soluble drugs (AAFE = 1.57, 21 Fa data). When the species difference in Cbile was ignored, Fa was over- and under-predicted for permeability and solubility limited cases, respectively. High Cbile in rats reduces the free fraction of drug molecules available for epithelial membrane permeation while increasing the solubility of poorly soluble drugs. CONCLUSION: The Fa values in rats were appropriately predicted by the GUT framework. This result would be of great help for a better understanding of species differences and model-informed preclinical formulation development.

The Critical Role of Passive Permeability in Designing Successful Drugs.

Passive permeability is a key property in drug disposition and delivery. It is critical for gastrointestinal absorption, brain penetration, renal reabsorption, defining clearance mechanisms and drug-drug interactions. Passive diffusion rate is translatable across tissues and animal species, while the extent of absorption is dependent on drug properties, as well as in vivo physiology/pathophysiology. Design principles have been developed to guide medicinal chemistry to enhance absorption, which combine the balance of aqueous solubility, permeability and the sometimes unfavorable compound characteristic demanded by the target. Permeability assays have been implemented that enable rapid development of structure-permeability relationships for absorption improvement. Future advances in assay development to reduce nonspecific binding and improve mass balance will enable more accurately measurement of passive permeability. Design principles that integrate potency, selectivity, passive permeability and other ADMET properties facilitate rapid advancement of successful drug candidates to patients.