ABSTRACT
Administration by the oral route is the most comm on and preferred m ethod by which drugs are presented for systemic effects. This process involves a drug given as a solid which undergoes dissolution followed by absorption through a biological m em brane into the systemic circulation (Davenport 1982; Davenport 1981). The main processes effecting the oral bioavailability of a drug are dissolution, permeability, enzymatic metabolism in the gastrointestinal m em brane and first-pass metabolism by the liver. For poorly soluble compounds, permeability of the biological m em brane is often not a major obstacle to absorption since the lipophilicity of a drug, which facilitates par titioning into the cell, generally increases as the solubility decreases (Grant and Higuchi 1990; Amidon and Williams 1982). Therefore, oral bioavailability of waterinsoluble drugs is often dependent upon the rate of dissolution of the drug in the gas trointestinal tract (Oh, Curl, and Amidon 1993). Furthermore, since the contents of the intestine and the com ponents of the intestinal m em brane vary along the GI tract and the dissolution occurs over a greater region of the GI tract, limited and variable or erratic oral absorption is generally associated with water-insoluble drugs.
