The U.S Food and Drug administration defines bioavailability as "The rate and extent to which the active drug ingredient or therapeutic moiety is absorbed from a drug product and become available at the site of drug action." Many studies illustrate that difference in manufacturing procedures, as well as the composition of the dosage form; can affect the bioavailability of a drug product. The importance of bioavailability is related to the drug action. A pharmacological response occur when drug

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... ith receptor after administration. A pharmacological activity can only be observed above the minimum effective concentration, hence that concentration of the drug, which above MEC is required for drug. The solubility of poorly bioavailability drug can be enhanced by the pharmaceutical approach which involves modification of formulation, manufacturing process or the physico-chemical properties of the drug without changing the chemical structure or by the pharmacokinetic approach in which pharmacokinetic of the drug is altered or the biologic approach where the route of drug administration can be changed. The methods used for the enhancement of bioavailability are as follows: Particle size reduction, use of surfactants, use of salt forms, use of metastable polymorphs etc.