Intestinal absorption and drug levels

Gastrointestinal (GI) drug absorption is influenced by many factors ranging from drug properties to intestinal morphology or drug–drug interactions. Drug bioavailability is potentially influenced by GI diseases or surgery, but the clinical significance of this impact is drug specific and often unpredictable. If the optimal efficacy of a pharmacological treatment in a patient with concomitant GI disease or resection is important, the following factors should be considered: is there evidence for sufficient drug efficacy in patients with comparable GI pathology? What is the absorption site of the drug and which parts of the GI tract are affected by the disease/resection? In general, non-modified-release, non-enteric coated or liquid formulations are advantageous in case of a disturbed GI tract. Clinical efficacy and, if possible, drug blood concentration levels should be monitored. Dose titration should be performed carefully to counterbalance maximal efficacy and the risk for potential side effects. If ineffectiveness of the drug is suspected, application pathways besides oral administration or alternative drugs should be evaluated.