What Is Ethosuximide?

Ethosuximide is a succinimide anticonvulsant medication FDA-approved for the treatment of absence seizures (petit mal) in patients aged 3 and older. It is considered a first-line treatment for absence seizures and has been used for decades. Ethosuximide is available as both a generic and under the brand name Zarontin, manufactured by Pfizer. It is taken orally as a capsule or liquid solution, typically once or twice daily.

How does Ethosuximide work?

Ethosuximide works by blocking T-type voltage-gated calcium channels in thalamocortical neurons in the brain. These channels are responsible for generating the low-threshold calcium currents that produce the characteristic 3 Hz spike-and-wave discharges seen in absence seizures. By suppressing these abnormal electrical signals, Ethosuximide prevents the brief lapses in consciousness that define absence seizures.

What doses are available for Ethosuximide?

• 250 mg capsules — available in generic form
• 250 mg/5 mL oral solution (syrup) — available as brand Zarontin and generic

Adults typically take 500 mg to 1,500 mg daily, while children aged 3–6 usually start at 250 mg daily. Your doctor will adjust the dose based on seizure control and tolerability.

How hard is it to find Ethosuximide in stock?

Ethosuximide scores a 55 out of 100 on our findability scale, meaning it can be moderately difficult to locate in stock. Because it treats a relatively uncommon condition (absence seizures), many pharmacies don't keep it on their shelves. While there is no active FDA-listed shortage, spot shortages at individual pharmacies are common due to low demand and a limited number of manufacturers. If your local pharmacy doesn't have it, you may need to call around or use Medfinder to locate a pharmacy that has Ethosuximide available.

Who Can Prescribe Ethosuximide?

Ethosuximide is most commonly prescribed by:

• Neurologists — specialists in brain and nervous system disorders
• Pediatric Neurologists — since absence seizures most often occur in children
• Epileptologists — neurologists who specialize specifically in epilepsy
• Pediatricians — may initiate treatment in children with absence seizures
• Primary Care Physicians — less commonly, but may manage stable patients

Telehealth consultations are also available for Ethosuximide prescriptions in many states.

Is Ethosuximide a controlled substance?

No, Ethosuximide is not a controlled substance. It is not classified under any DEA schedule. This means there are no special prescribing restrictions, refill limits, or ID requirements beyond a standard prescription. Pharmacies can transfer prescriptions between locations and refills can be called in by your doctor.

Common Side Effects of Ethosuximide

• Nausea and vomiting
• Stomach upset and loss of appetite
• Diarrhea
• Drowsiness and lethargy
• Dizziness
• Headache
• Hiccups
• Difficulty concentrating

Most gastrointestinal side effects improve by taking Ethosuximide with food. Serious but rare side effects include Stevens-Johnson syndrome, blood disorders (agranulocytosis, aplastic anemia), and suicidal thoughts. Contact your doctor immediately if you develop a rash, unusual bleeding, or mood changes.

Alternative Medications to Ethosuximide

• Valproic Acid (Depakote/Depakene) — a first-line alternative for absence seizures with similar efficacy. Also treats generalized tonic-clonic seizures. Has more side effects including weight gain and is highly teratogenic.
• Lamotrigine (Lamictal) — a second-line option for absence seizures. Less effective than Ethosuximide but better tolerated overall. Often preferred in women of childbearing age.
• Clonazepam (Klonopin) — a benzodiazepine sometimes used adjunctively for absence seizures. Risk of tolerance and dependence limits long-term use.
• Clobazam (Onfi) — a benzodiazepine with some evidence for absence seizures. Typically used as add-on therapy.

Drug Interactions with Ethosuximide

• Phenytoin, Carbamazepine, Phenobarbital — these enzyme inducers can reduce Ethosuximide levels, potentially decreasing seizure control
• Isoniazid — may slow Ethosuximide metabolism and increase blood levels
• Valproic Acid — variable effects on Ethosuximide levels; monitor closely when used together
• Rifampicin — increases clearance of Ethosuximide
• CNS Depressants (opioids, benzodiazepines, alcohol) — additive sedation when combined with Ethosuximide
• Lamotrigine — Ethosuximide may reduce Lamotrigine levels by up to 37% in children

Always inform your doctor of all medications you take, including over-the-counter drugs and supplements.

Final Thoughts on Ethosuximide

Ethosuximide remains one of the most effective and well-established treatments for absence seizures, with decades of clinical use supporting its safety and efficacy. While it can be moderately difficult to find in stock at some pharmacies due to low demand and limited manufacturers, it is not currently in a formal shortage. Generic versions are available at significant savings with coupon cards — as low as $32 per month. If you're having trouble finding Ethosuximide at your local pharmacy, use Medfinder to search for nearby pharmacies that have it available. Never stop taking Ethosuximide abruptly, as this can trigger absence status epilepticus.