Interactions
Valproic acid may interact with carbamazepine, as valproates inhibit microsomal epoxide hydrolase (mEH), the enzyme responsible for the breakdown of carbamazepine-10,11 epoxide (the main active metabolite of carbamazepine) into inactive metabolites. By inhibiting mEH, valproic acid causes a buildup of the active metabolite, prolonging the effects of carbamazepine and delaying its excretion.
Valproic acid also decreases the clearance of amitriptyline and nortriptyline.
Aspirin may decrease the clearance of valproic acid, leading to higher-than-intended serum levels of the anticonvulsant. Also, combining valproic acid with the benzodiazepine clonazepam can lead to profound sedation and increases the risk of absence seizures in patients susceptible to them.
Valproic acid and sodium valproate reduce the apparent clearance of lamotrigine (lamictal). In most patients, the lamotrigine dosage for coadministration with valproate must be reduced to half the monotherapy dosage.
Valproic acid is contraindicated in pregnancy, as it decreases the intestinal reabsorption of folate (folic acid), which leads to neural tube defects. Because of a decrease in folate, megaloblastic anemia may also result. Phenytoin also decreases folate absorption, which may lead to the same adverse effects as valproic acid.
Read more about this topic: Valproic Acid
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