clinical pharmacology
Drug Excretion
Introduction
The kidneys are the principal organs for excreting water-soluble substances. The biliary system contributes to excretion to the degree that drug is not reabsorbed from the gastrointestinal (GI) tract. Generally, the contribution of intestine, saliva, sweat, breast milk, and lungs to excretion is small, except for exhalation of volatile anesthetics. Excretion via breast milk may affect the breastfeeding infant (see table Some Drugs Contraindicated for Breastfeeding Mothers ). Hepatic metabolism often increases drug polarity and water solubility. The resulting metabolites are then more readily excreted. (See also Overview of Pharmacokinetics .) 