The oral route is the most preferred route for drug administration because of patient compliance. Following oral administration, a drug has to cross several biological barriers before reaching the systemic circulation by transcellular or paracellular transports. Oral drug absorption and bioavailability are influenced by the physicochemical, formulation and physiological variables. Oral absorption of drugs is controlled by dissolution from the dosage form, and permeability across the gastrointestinal membrane. Rate limiting step in absorption is the permeability for compounds with low permeability, and dissolution for compounds with low solubility. According to Food and Drug Administration (FDA) Biopharmaceutics Classification System (BCS)-based biowaiver guidance and European Medicines Agency (EMA) Guideline on the Investigation of Bioequivalence, permeability class of a drug substance can be determined using different methods. The aim of this study was to evaluate the methods in detail recommended by FDA and EMA for determination of permeability of drugs. We surveyed the literature as to the pros and cons of the methods recommended by the health authorities for assessment of permeability. In general, a single method is sufficient for determination of permeability. When a single method fails to demonstrate a permeability classification, two different methods may be used.
Key words: Permeability, Food and Drug Administration (FDA), Biopharmaceutics Classification System (BCS), oral absorption, European Medicines Agency (EMA)
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