Zarontin is less likely than many other antiepileptic drugs to interact with other medications. Nevertheless, it's advisable to question patients or family members about the use of prescription and OTC medications, herbal products, vitamins, alcohol, and other substances when prescribing Zarontin. Usually all necessary medications can be used, but the dosages may need to be adjusted to achieve therapeutic levels.

Effects of Zarontin (ethosuximide) on other drugs
Zarontin has little effect on other medications. It may elevate blood levels of phenytoin (Dilantin, Phenytek) somewhat, but the clinical significance is unclear.

Effects of other drugs on Zarontin (ethosuximide)
Valproate (Depakote, Depakene, valproic acid) may slightly increase blood levels of ethosuximide, but it is unclear whether the effect is clinically significant. The combination of these two medications is often beneficial.

Administering ethosuximide along with isoniazid, ritonavir, or erythromycin may elevate serum levels of ethosuximide to a greater extent because of their inhibitory effects on enzymes responsible for its metabolism in the liver.

The level of ethosuximide is reduced if it is taken concurrently with enzyme-inducing medications, including:

• carbamazepine (Tegretol, Carbatrol)
• phenytoin (Dilantin, Phenytek)
• primidone (Mysoline)
• phenobarbital
• rifampin

AED Interaction Sheets:
Seizure drugs are often affected by drug-drug interactions. Print these informative sheets for practical help.

• Interaction sheet for ethosuximide (Zarontin)

Reviewed February 2004 by Barry Gidal, PharmD, epilepsy.com Editorial Board.