ABSTRACT
The scope of preformulation studies has changed significantly over the past couple of decades with the availability of techniques to study the release and permeation characteristics of lead compounds. Drug absorption depends on the release of the drug substance from the drug product, the solubility, and the permeability across the gastrointestinal (GI) tract. The diffusion layer model of dissolution assumes that the dissolution of drug at the solid–liquid interface into a concentrated layer surrounding the solid particle is more rapid than the diffusion of dissolved drug from that layer into the bulk solution. The methods can be used to determine the permeability of a drug substance from the GI tract. Which includes in vivo intestinal perfusion studies in humans; in vivo or in situ intestinal perfusion studies using suitable animal models; in vitro permeation studies using excised human or animal intestinal tissues; or in vitro permeation studies across a monolayer of cultured epithelial cells.
