The most important property of a dosage form is its ability to deliver the active ingredients to the site of action in an amount sufficient to elicit the desired pharmacological response. This property of the dosage form has been variously referred to its physiological availability, biological availability or bioavailability. "Bioavailability is defined more precisely as the rate and extent of absorption of a drug from its dosage form in to the systemic circulation". Many of the new drugs (APIs) exhibits low and variable dissolution and bioavailability due to their poor aqueous solubility at physiological pHs and consequent low dissolution rate. These drugs are classified as class II drugs under BCS classification. Biopharmaceutical Classification System (BCS) guidance was provided by USFDA to improve the efficiency of drug product development process in the BCS, drugs are grouped into four major classes basing on the solubility and permeability as follows: I. Class I (High solubility and High permeability) II. Class II (Low solubility and High permeability) III. Class III (high solubility and low permeability) IV. Class IV (Low solubility and Low permeability).