Carbamazepine and oxcarbazepine decrease phenytoin metabolism through inhibition of CYP2C19.

Epilepsy Res

Department of Pharmaceutics, University of Washington, Seattle, WA 98195-7610, USA.

Published: December 2002

Multiple studies suggest that phenytoin concentrations increase with CBZ co-medication. This study evaluated the hypothesis that CBZ and/or its major metabolite (CBZE) inhibit CYP2C19-mediated phenytoin metabolism using human liver microsomes and cDNA-expressed CYP2C19. Oxcarbazepine (OXC), and its 10-monohydroxy metabolite (MHD) were also evaluated. CBZ and MHD inhibited CYP2C19-mediated phenytoin metabolism at therapeutic concentrations. Thus, administration of CBZ and OXC with CYP2C19 substrates with narrow therapeutic ranges should be done cautiously.

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http://dx.doi.org/10.1016/s0920-1211(02)00188-2DOI Listing

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