Editing Carbamazepine (section)

=== Pharmacokinetics ===
[[File:Carbamazepine metabolism.svg|class=skin-invert-image|thumb|upright=0.7|'''Metabolism.''' Top: carbamazepine • middle: carbamazepine-10,11-[[epoxide]], the [[active metabolite]] • bottom: carbamazepine-10,11-[[diol]], an inactive metabolite, which is then [[Glucuronidation|glucuronidized]]]]

Carbamazepine is relatively slowly but practically completely absorbed after administration by mouth. Highest concentrations in the [[blood plasma]] are reached after 4 to 24 hours depending on the dosage form. [[Slow release]] tablets result in about 15% lower absorption and 25% lower peak plasma concentrations than ordinary tablets, as well as in less fluctuation of the concentration, but not in significantly lower [[Cmin|minimum concentration]]s.<ref name="PubChem">{{cite web |title=Carbamazepine |url= https://pubchem.ncbi.nlm.nih.gov/compound/2554 |access-date=6 May 2021|work = PubChem | publisher = National Library of Medicine, National Institutes of Health, U.S. Department of Health and Human Services }}</ref><ref name="AC">{{cite book|title=Austria-Codex| veditors = Haberfeld H |at=Tegretol retard 400 mg-Filmtabletten|publisher=Österreichischer Apothekerverlag|location=Vienna|year=2021|language=German}}</ref>

In the circulation, carbamazepine itself comprises 20 to 30% of total residues. The remainder is in the form of [[metabolite]]s; 70 to 80% of residues is bound to [[plasma protein]]s. Concentrations in breast milk are 25 to 60% of those in the blood plasma.<ref name="AC" />

Carbamazepine itself is not pharmacologically active. It is activated, mainly by CYP3A4, to carbamazepine-10,11-[[epoxide]], which is solely responsible for the drug's anticonvulsant effects. The epoxide is then inactivated by microsomal epoxide hydrolase (mEH) to carbamazepine-''trans''-10,11-[[diol]] and further to its [[glucuronide]]s. Other metabolites include various [[hydroxyl]] derivatives and carbamazepine-''[[nitrogen|N]]''-glucuronide.<ref name="AC" />

The [[plasma half-life]] is about 35 to 40 hours when carbamazepine is given as single dose, but it is a strong [[enzyme inducer|inducer]] of liver enzymes, and the plasma half-life shortens to about 12 to 17 hours when it is given repeatedly. The half-life can be further shortened to 9–10 hours by other enzyme inducers such as [[phenytoin]] or [[phenobarbital]]. About 70% are excreted via the urine, almost exclusively in form of its metabolites, and 30% via the faeces.<ref name="PubChem" /><ref name="AC" />