STRATEGIES FOR ENHANCING ORAL BIOAVAILABILITY OF POORLY SOLUBLE DRUGS

Bioavailability is defined as the rate and extent of absorption of unchanged drug from its dosage form in to the systemic circulation. A drug with poor bioavailability is one with poor aqueous solubility, slow dissolution rate in biological fluids, poor stability of drug dissolved at physiological pH, poor permeation through biomembrane, extensive presystemic metabolism. Oral ingestion is most convenient and commonly employed route of drug delivery due to its ease of administration, high patient compliance, cost effectiveness, least sterility constraints, and flexibility in the design of dosage form. As a result, many of the generic drug companies are inclined more to produce bioequivalent oral drug products. The main technologies to achieve the enhanced oral bioavailability of drugs with poor aqueous solubility include the use of solid dispersions, micronization, nanonization, solid lipid nanoparticles and colloidal drug delivery systems etc. Colloidal drug delivery systems include microemulsions, self emulisifying drug delivery systems, liposomes, self micro emulsifying drug delivery systems (SMEDDS). One of the challenges in formulating micro emulsions, self emulsifying drug delivery systems is the limited bioavailability of formulation components with GRAS (generally regarded as safe) status. Bioavailability of the drug is the most important factor that controls the formulation of drug as well as the therapeutic efficacy of the drug, hence the most critical factor in the formulation development.