Editing ADME (section)

=== Excretion ===
{{Main article|Excretion }}

Compounds and their [[metabolite]]s need to be removed from the body via [[excretion]], usually through the [[kidney]]s (urine) or in the feces. Unless excretion is complete, accumulation of foreign substances can adversely affect normal metabolism.

There are three main sites where drug excretion occurs. The kidney is the most important site and it is where products are excreted through urine. Biliary excretion or fecal excretion is the process that initiates in the liver and passes through to the gut until the products are finally excreted along with waste products or feces. The last main method of excretion is through the lungs (e.g. anesthetic gases).

Excretion of drugs by the kidney involves 3 main mechanisms:
* [[Glomerular filtration]] of unbound drug.
* Active secretion of (free & protein-bound) drug by transporters (e.g. anions such as [[urate]], [[penicillin]], [[glucuronide]], [[sulfate]] conjugates) or cations such as [[choline]], [[histamine]].
* Filtrate 100-fold concentrated in tubules for a favorable concentration gradient so that it may be secreted by passive diffusion and passed out through the urine.