An active metabolite is an active form of a drug after it has been processed by the body.
Metabolites of drugs
An active metabolite results when a drug is metabolized by the body into a modified form which continues to produce effects in the body. Usually these effects are similar to those of the
parent drug but weaker, although they can still be significant (see e.g.
11-hydroxy-THC,
morphine-6-glucuronide). Certain drugs such as
codeine
Codeine is an opiate and prodrug of morphine mainly used to treat pain, coughing, and diarrhea. It is also commonly used as a recreational drug. It is found naturally in the sap of the opium poppy, ''Papaver somniferum''. It is typically use ...
and
tramadol have metabolites (
morphine
Morphine is a strong opiate that is found naturally in opium, a dark brown resin in poppies ('' Papaver somniferum''). It is mainly used as a pain medication, and is also commonly used recreationally, or to make other illicit opioids. Ther ...
and
''O''-desmethyltramadol respectively) that are stronger than the parent drug
and in these cases the metabolite may be responsible for much of the therapeutic action of the parent drug. Sometimes, however, metabolites may produce toxic effects and patients must be monitored carefully to ensure they do not build up in the body. This is an issue with some well-known drugs, such as
pethidine
Pethidine, also known as meperidine and sold under the brand name Demerol among others, is a synthetic opioid pain medication of the phenylpiperidine class. Synthesized in 1938 as a potential anticholinergic agent by the German chemist Otto Ei ...
(meperidine) and
dextropropoxyphene
Dextropropoxyphene is an analgesic in the opioid category, patented in 1955 and manufactured by Eli Lilly and Company. It is an optical isomer of levopropoxyphene. It is intended to treat mild pain and also has antitussive (cough suppressant) ...
.
Prodrugs
Sometimes drugs are formulated in an inactive form that is designed to break down inside the body to form the active drug. These are called
prodrugs. The reasons for this type of formulation may be because the drug is more stable during manufacture and storage as the prodrug form, or because the prodrug is better absorbed by the body or has superior
pharmacokinetics
Pharmacokinetics (from Ancient Greek ''pharmakon'' "drug" and ''kinetikos'' "moving, putting in motion"; see chemical kinetics), sometimes abbreviated as PK, is a branch of pharmacology dedicated to determining the fate of substances administered ...
(e.g.,
lisdexamphetamine).
References
Further reading
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{{Combined substance use and adulteration
Pharmacokinetics
Metabolism