New Drug Delivery Systems for Stable Oral Absorption: Theory, Strategies, and Applications

The oral dosage route still remains the most common and preferred route for drug administration due to convenient handling, high patient compliance, and cost-effectiveness. However, the oral absorption of drugs can be a complex process depending upon: (i) physicochemical properties of the drug (e.g., pK_a, lipophilicity, solubility), (ii) pharmaceutical factors (e.g., dosage form), and (iii) physiological factors (e.g., gastrointestinal pH values, gastric emptying rate, gastric and intestinal pH, metabolism). Oral administration of drugs sometimes leads to poor and/or variable oral bioavailability, possible leading to unstable clinical outcomes. To offer stable and improved pharmacokinetic behavior of drugs, a number of formulation approaches have been developed with a focus on enhancement of the solubility, dissolution rate, and oral bioavailability of drugs. To provide new formulation platforms for better and safe medication, it is considered essential to understand the physicochemical, biochemical, metabolic, and biological barriers which limit overall drug bioavailability in more detail. The review article considers several crucial factors affecting oral absorption of drug substances. This article also describes the recent progress in formulation approaches to achieve stable and improved biopharmaceutical properties of orally-taken drugs.