Provider Briefing: Ethosuximide Availability in 2026

Ethosuximide remains the first-line agent for absence seizures, backed by Level A evidence and decades of clinical experience. Yet an increasing number of patients are reporting difficulty filling their prescriptions. This briefing covers the current availability landscape, prescribing implications, and practical tools to help your patients maintain uninterrupted therapy.

Current Shortage Status

As of early 2026, Ethosuximide is not formally listed on the FDA or ASHP drug shortage databases. However, the practical reality is more nuanced. Ethosuximide occupies a unique position in the pharmaceutical market: it is a highly effective, guideline-recommended medication with a very small patient population. This creates a paradox where the drug is technically available but functionally difficult for many patients to obtain.

The absence of a formal shortage listing should not be interpreted as full availability. Reports from patients and pharmacists indicate persistent spot shortages at the retail pharmacy level, particularly at chain pharmacies that stock based on dispensing volume.

Timeline: How We Got Here

Ethosuximide has been available since the 1960s and has maintained a stable role in epilepsy management throughout its history. Key factors shaping the current landscape include:

• 1960s–2000s: Ethosuximide established as the standard of care for childhood absence epilepsy. Multiple manufacturers produced the drug.
• 2010: The landmark NIH-funded trial confirmed Ethosuximide's superiority over Lamotrigine and equivalent efficacy to Valproic Acid for absence seizures, reinforcing its first-line status.
• 2010s–2020s: Consolidation in the generic pharmaceutical industry reduced the number of Ethosuximide manufacturers. Pfizer remained the primary brand-name producer (Zarontin).
• 2024–2026: Ongoing supply chain variability. While no prolonged nationwide shortage has occurred, intermittent regional and pharmacy-level stockouts have become more common due to limited manufacturing capacity and low commercial incentive.

Prescribing Implications

The availability challenges with Ethosuximide have several clinical implications for prescribers:

Formulation Flexibility

Ethosuximide is available as 250 mg capsules and a 250 mg/5 mL oral solution. When writing prescriptions, consider allowing pharmacist substitution between formulations. Specifying "may substitute oral solution for capsules" can help pharmacies fill prescriptions from available stock.

Therapeutic Drug Monitoring

The therapeutic range for Ethosuximide is 40–100 μg/mL. When patients switch pharmacies, formulations, or manufacturers, consider checking trough levels to ensure continued therapeutic dosing. The oral solution has faster absorption than capsules, which may affect peak levels.

Discontinuation Risk

Abrupt discontinuation of Ethosuximide can precipitate absence status epilepticus. Patients who cannot fill their prescriptions are at risk of involuntary medication gaps. Proactive communication about refill planning is essential.

Alternative Agents

When Ethosuximide is truly unavailable, the evidence-based alternatives are:

• Valproic Acid: Equivalent efficacy for absence seizures (58% seizure freedom rate vs. 53% for Ethosuximide). Also controls generalized tonic-clonic seizures. However, greater adverse effect burden (weight gain, hepatotoxicity, teratogenicity) and contraindicated in women of childbearing potential unless other options have failed.
• Lamotrigine: Inferior efficacy (21% seizure freedom rate) but better tolerability. Preferred in women of childbearing age. Requires slow titration (6–8 weeks to therapeutic dose).
• Clobazam: Moderate evidence for use in epilepsy with eyelid myoclonia and as adjunctive therapy. Risk of tolerance with long-term use.

For detailed alternative comparisons, see Alternatives to Ethosuximide.

The Availability Picture: Why Patients Can't Find It

Understanding why patients struggle to find Ethosuximide helps inform clinical conversations:

• Low dispensing volume: Most retail pharmacies stock based on demand. A pharmacy that fills 0–1 Ethosuximide prescriptions per month will not maintain inventory.
• Limited manufacturers: Few companies produce generic Ethosuximide capsules. Pfizer produces the brand-name Zarontin oral solution.
• Wholesaler allocation: When supply is constrained, wholesalers prioritize high-volume accounts, which can leave smaller pharmacies underserved.
• Patient geography: Rural and underserved areas are disproportionately affected, as they have fewer pharmacy options.

Cost and Access Considerations

Cost can be a secondary barrier even when supply is available:

• Cash price: $200–$580 per month without insurance
• With discount cards: Generic Ethosuximide as low as $32 (GoodRx) or $36 (SingleCare)
• Insurance: Most plans cover generic Ethosuximide without prior authorization. Brand Zarontin may require PA.
• Patient assistance: Pfizer RxPathways (1-844-989-4366) offers co-pay assistance and a patient assistance program for eligible patients

For a detailed cost guide to share with patients, see How to Save Money on Ethosuximide.

Tools and Resources for Your Practice

Several tools can help you and your patients navigate Ethosuximide availability:

Medfinder for Providers

Medfinder offers real-time pharmacy availability data that can be integrated into your workflow. Instead of asking patients to call multiple pharmacies, direct them to Medfinder to check Ethosuximide stock near their location.

Proactive Prescription Management

• Write prescriptions with formulation flexibility when clinically appropriate
• Encourage patients to refill 7–14 days before running out
• Identify 2–3 pharmacies in your area that reliably stock Ethosuximide and share this information with patients
• Consider recommending independent pharmacies, which are often more willing to special-order niche medications

EHR Documentation

Document any supply-related medication changes in the patient's chart. If a patient must temporarily switch to Valproic Acid or Lamotrigine due to Ethosuximide unavailability, note the clinical rationale and plan for returning to Ethosuximide when supply is restored.

Looking Ahead

The structural factors driving Ethosuximide availability challenges—small patient population, limited manufacturers, and low commercial incentive—are unlikely to change significantly in the near term. Providers should anticipate ongoing intermittent supply issues and plan accordingly.

Key actions for 2026:

• Proactively discuss supply challenges with Ethosuximide patients
• Have a documented backup plan (alternative medication, alternative pharmacy) in each patient's chart
• Direct patients to Medfinder as a first step when they can't find their medication
• Report persistent supply issues to the FDA Drug Shortage Staff (drugshortages@fda.hhs.gov) to help flag emerging problems

Final Thoughts

Ethosuximide remains an irreplaceable medication for many patients with absence epilepsy. While it is not in formal shortage, the functional availability challenges are real and likely to persist. By building awareness of the issue, having backup plans ready, and leveraging tools like Medfinder, providers can help ensure their patients maintain continuous access to this essential therapy.

For the patient-facing version of this update, see Ethosuximide Shortage Update: What Patients Need to Know. For a complete provider workflow guide, read How to Help Your Patients Find Ethosuximide in Stock.