Drugs are eliminated from the body either unchanged or as metabolites

Excretory organs, (except the lung ), eliminate polar compounds more efficiently

lipid-soluble drugs are not readily eliminated until they are metabolized to more polar compounds

Renal excretion of unchanged drug is a major route of elimination for 25%–30% of drugs administered to humans

Excretion of drugs in breast milk is important not because of the amounts eliminated (which are small) but because the excreted drugs may affect the nursing infant.

Excretion from the lung is important mainly for the elimination of anesthetic gases

Substances excreted via Biliary fecal excretion are principally unabsorbed orally ingested drugs or drug metabolites either excreted in the bile or secreted directly into the intestinal tract and not reabsorbed.

Excretion Organs of Drugs

The phenomenon Affects the intestinal excretion of drugs especially those conjugated with glucuronic acid in the liver.

Conjugated drugs and their metabolites that are secreted into bile are carried by the biliary ducts to the duodenum.

Glucuronides that are eliminated in bile can be hydrolyzed by glucuronidases in the intestine by bacterial flora and the free drug can be reabsorbed (Enterohepatic circulation).

Excretion of drugs into sweat, saliva, and tears is quantitatively unimportant.

Because milk is more acidic than plasma, basic compounds may be slightly concentrated in this fluid; conversely, the concentration of acidic compounds in the milk is lower than in plasma.

Nonelectrolytes (e.g., ethanol and urea) readily enter breast milk and reach the same concentration as in plasma, independent of the pH of the milk.

Breast milk can also contain heavy metals from environmental exposures.

The administration of drugs to breastfeeding women carries the general caution that the suckling infant will be exposed to some extent to the medication or its metabolites. (Maternogenecity).

Although excretion into hair and skin is quantitatively unimportant, sensitive methods of detection of drugs in these tissues have forensic significance

important route of excretion of most drugs

Excretion of drugs and metabolites in the urine involves three distinct processes

Active tubular secretion.

Clinical notes