The Effects of Dose Volume and Excipient Dose on Luminal Concentration and Oral Drug Absorption.

Excipient concentrations in the gastrointestinal luminal fluids can influence the absorption of poorly water-soluble drugs when dosed orally with solubilizing excipients, and poorly permeable drugs when dosed with permeation-enhancing excipients. This report examines how dose volume, excipient dose level, volume of water chaser, and gastric fluid volume influence luminal excipient concentrations, and how these could differ from preclinical species and humans. Gastric concentrations of excipient resulting immediately after dosing typical formulations containing a solubilizing excipient are estimated in preclinical species and humans.

Optimizing Oral Bioavailability in Drug Discovery: An Overview of Design and Testing Strategies and Formulation Options.

For discovery teams working toward new, orally administered therapeutic agents, one requirement is to attain adequate systemic exposure after oral dosing, which is best accomplished when oral bioavailability is optimized. This report summarizes the bioavailability challenges currently faced in drug discovery, and the design and testing methods and strategies currently utilized to address the challenges. Profiling of discovery compounds usually includes separate assessments of solubility, permeability, and susceptibility to first-pass metabolism, which are the 3 most likely contributors to incomplete oral bioavailability.

Absorption enhancers: applications and advances.

Absorption enhancers are functional excipients included in formulations to improve the absorption of a pharmacologically active drug. The term absorption enhancer usually refers to an agent whose function is to increase absorption by enhancing membrane permeation, rather than increasing solubility, so such agents are sometimes more specifically termed permeation enhancers. Absorption enhancers have been investigated for at least two decades, particularly in efforts to develop non-injection formulations for peptides, proteins, and other pharmacologically active compounds that have poor membrane permeability.

Criteria for selecting pharmacokinetic repeat study samples.

The pharmacokinetic (PK) repeat study sample, selected by the study pharmacokineticist, requires repeat bioanalysis because the concentration is incongruous with drug plasma concentration versus time profile. The inconsistency could be due to a number of reasons, including the detectable drug concentration in a predose sample or a sample from a placebo control group or a significant double peak in the terminal phase of an individual plasma concentration versus time profile that is not consistent with the profiles from other subjects in the same dose group. The justification for selecting the PK repeat sample should be clearly documented.

Limited interaction between tacrolimus and P-glycoprotein in the rat small intestine.

The significance of intestinal P-glycoprotein (P-gp) in determining the oral bioavailability of tacrolimus has been still controversial. In this study, we reevaluated the interaction of tacrolimus with P-gp in the rat small intestine, by evaluating its absorption from the rat small intestine and its modulating effect on the absorption of known P-gp substrates (digoxin, methylprednisolone, and vinblastine). Intestinal absorption of tacrolimus itself was as extensive as other P-gp modulators such as cyclosporine and verapamil.