Predicting the oral absorption of poorly soluble drugs

The oral administration of a drug is the most frequent and convenient route of administration, and formulation researchers normally strive to formulate drugs so that they can be administered orally. Exceptions to this general rule occur when the site of action is accessible (e. g. creams and ointments for local treatment of skin conditions) or when the drug cannot be absorbed from the gastrointestinal tract (e. g. proteins like insulin). In most cases, orally administered drugs are intended to act systemically, so they have to be absorbed during their passage through the gastrointestinal tract. There are only a few drugs which are administered orally and are intended to act locally, e. g. some antacids like calcium carbonate or sucralfate, drugs used for pancreatic enzyme replacement therapy, and anti-inflammatory drugs which are used for the therapy of Crohn’s disease and ulcerative colitis [1].