Ethosuximide (Zarontin, Pfizer)
Ethosuximide is a drug of choice for pure absence (petit mal) seizures. It is not effective against generalized tonic-clonic (grand mal) seizures. Ethosuximide has been around since the early 1950's. If absence seizures are intermixed with convulsions, then a broad-spectrum antiepileptic drug such as Depakote, Lamictal, Topamax, or Zonegran is required. Alternatively, two drugs can be used, such as Zarontin plus Dilantin or Tegretol.
Ethosuximide has a half-life of several days in the blood, which would allow single daily dosing. However, GI sensitivity often requires splitting the dose.
Summary Data for Ethosuximide
Pill sizes: 250 mg capsules (red, shiny).
Liquid for oral: 250 mg/5 ml suspension.
Injectable: none.
Typical adult dose: 500 mg per day in 2 divided doses, increase over a few weeks to 500-1500 mg/d in 2 or 3 divided doses. Half-life would permit daily dosing, but GI side effects might require splitting the dose.
Typical pediatric dose: Start with 10 mg/kg/d in 2 or 3 divided doses. Increase over weeks to 15-40 mg/kg/d.
Metabolism: Mainly liver, 3A4 system.
Half-life: 30-40 hr in kids, 50-60 in adults
Serum levels: 40-100 mcg/ml
Pregnancy: Category C - can cause birth defects in animals, unknown in humans.
Drugs that raise ESM levels: valproic acid
ESM decreases effects of other drugs: Lamotrigine, estrogen (may make birth control pills less effective)
Dangerous Side Effects
Rare serious behavior problems or psychosis, rare blood counts
Common Side Effects
GI upset, sleepiness.
Other Side Effects
Dizziness, headaches, rash.