Penetration enhancers have been applied to improve the absorption of poorly permeable, hydrophilic drugs or macromolecules. Permeation enhancers that have been used successfully for oral drug development include medium-chain fatty acids like caprylic acid or caprate, or its amino acid ester like Salcaprozate sodium (SNAC). The above-mentioned permeation/penetration enhancers have a surfactant-like activity where they perturb the intestinal epithelium, promoting transcellular or paracellular absorption.