biotransformation

Think of biotransformation as the body's chemistry workshop. Many drugs are oily, fat-loving molecules that the kidneys cannot easily flush out in urine. The body solves this by chemically remodeling the drug — usually in the liver — into versions that are more water-soluble and easier to pour down the drain.

Technically, biotransformation is the enzyme-catalyzed chemical alteration of a drug into one or more metabolites. It is traditionally divided into phase I reactions, which add or expose a reactive chemical handle (often by oxidation), and phase II reactions, which attach a bulky polar group to that handle so the molecule can be excreted.

An important caveat: biotransformation does not always mean inactivation. Some drugs are metabolized into products that are equally or more active, and a few are even more toxic than the parent compound. So the term describes a chemical change, not necessarily a 'detoxification.'