Adding topiramate to valproic acid.
- Valproic acid is principally metabolized by CYP2C9, CYP2C19, CYP2A6 and UDP-glucuronosyltransferases. Valproic acid is an inhibitor of the enzymes CYP2C9, epoxide-hydroxylase and UDP-glucuronosyltransferases.
- Topiramate induces CYP3A4 and is an inhibitor of CYP2C19.
- Start topiramate according to general dosing advice. Pharmacologic response to the drugs should be monitored more closely following addition or withdrawal of one or the other drug. 
- Topiramate has been shown to produce a small but significant increase in valproate clearance, reducing plasma levels.
- Topiramate plasma levels are increased by about 15% by valproate, which could be important if valproic acid is withdrawn.
- Farmacotherapeutisch Kompas; Toxicologie (dutch)
- Farmacotherapeutisch Kompas - valproinezuur (dutch)
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- KNMP; Informatorium Medicamentorum 2015; Monografie "valproaat" (Dutch)
- Interactions between valproic acid and topiramate on drugs.com
- Bazire S, Psychotropic Drug Directory 2007, HealthComm UK Limited, Aberdeen, 2007.
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