DailyMed-verified antiseizure indications

Indication / use

Label / evidence summary: Celontin and generic methsuximide capsules: absence (petit mal) seizures refractory to other drugs.
Role: Maintenance
Class: Succinimide antiseizure medication

Indications checked 26 September 2026. Product, route, age, and treatment-role limits apply. A DailyMed listing alone does not establish FDA approval.

Celontin capsules U.S. label
Absence · No numeric age limits specified in this label · Maintenance
Absence seizures refractory to other drugs.
- Celontin capsules — brand-name package insert (PDF) ↗
- Original source ↗
Methsuximide capsules (generic) U.S. label
Absence · No numeric age limits specified in this label · Maintenance
Absence seizures refractory to other drugs.
- Representative source · Methsuximide capsules (ANI) — DailyMed label (PDF) ↗
- Representative source · DailyMed label page ↗

Formulations & strengths

U.S. product labels; strengths per capsule.

Capsule (Celontin)

Strengths: 300 mg
Product note: Oral capsule.

Celontin capsules — brand-name package insert (PDF) ↗

Brand & formulation labels

Each link names the product and formulation it covers. Archived labels do not establish current availability.

Dosing & administration

Adult / product-specific schedule: Label schedule: 300 mg/day for week 1; if needed, increase by 300 mg/day at weekly intervals over the next 3 weeks to 1,200 mg/day. Individualize to response and tolerability.
Pediatric: The label refers pediatric use to the same individualized schedule; it provides no separate weight-based regimen or numeric minimum age.
Titration / repeat dosing: Use the label schedule above; dose changes and withdrawal require clinician supervision.

Practical administration

Product instructions: Protect capsules from excessive heat. Do not use capsules with melted contents.

Celontin capsules — brand-name package insert (PDF) ↗

Dose adjustment & concentrations

Renal impairment: Extreme caution in renal disease; no numeric adjustment algorithm in the label.
Hepatic impairment: Extreme caution in liver disease; no numeric adjustment algorithm in the label.
Serum reference information: Measure N-desmethylmethsuximide. A small adult study reported 10–30 mcg/mL; this is not a universal target or a parent-drug range.

PubMed · Adult pharmacology study (1983; off-label focal seizures) ↗

Safety

Boxed warning: No boxed warning in the cited labels.
Contraindications: History of hypersensitivity to succinimides.
Serious precautions & monitoring: Blood dyscrasias (potentially fatal), systemic lupus erythematosus, serious skin reactions including Stevens–Johnson syndrome, and suicidal thoughts or behavior. Monitor blood counts, liver tests and urinalysis.

Celontin capsules — brand-name package insert (PDF) ↗

Common / selected adverse effects

Drowsiness
Dizziness / ataxia
Gastrointestinal symptoms
Headache
Blurred vision

Qualitative label summary; frequencies are not comparable across medicines.

Open product prescribing information ↗

Drug interactions: toxicity & clinical action

Partner / combination	Clinical effect	Clinical action
Phenytoin / phenobarbital	Concentrations may rise, including phenobarbital formed from primidone.	Monitor concentrations and toxicity when methsuximide changes.
Lamotrigine	Reduced concentrations reported in a pharmacokinetic study.	Monitor seizure control and concentrations during addition or withdrawal.
Valproate	Reduced concentrations reported in a clinical study.	Monitor levels and response; reassess dosing when methsuximide starts or stops.
Alcohol / sedating medicines	Additive impairment.	Review combined sedative effects.

Selected interactions; consult the exact product label and full regimen.

Pregnancy & contraception

Fetal / neonatal risk: Drug-specific fetal risk remains uncertain. The label recommends individualized assessment and pregnancy-registry enrollment.

Celontin capsules — brand-name package insert (PDF) ↗

Clinical evidence

Research summaries describe studied populations and outcomes; they do not add indications or constitute treatment recommendations.

Observational evidence

Trial summary

Study design / duration: Prospective uncontrolled pediatric add-on study; not a modern randomized registration trial.
Primary endpoint: At least 50% seizure-frequency reduction in the uncontrolled pediatric study.
Results: A prospective uncontrolled add-on study in 112 children with refractory epilepsies reported at least 50% seizure reduction in 40 after a mean 9.1 weeks. This heterogeneous study does not establish additional labeled indications or comparative superiority.
Confidence intervals: No confidence interval is supplied in the abstract.
Discontinuations: Not summarized as a comparable trial discontinuation rate.
Exposure duration: Mean initial observation 9.1 weeks; 39 continuing patients were reassessed after a mean 3.7 years.

PubMed · Uncontrolled pediatric add-on study (2001) ↗

Trial publications

PubMed · Uncontrolled pediatric add-on study (2001) ↗

Comparative evidence

Findings: No controlled head-to-head estimate is provided by the cited studies.

Mechanism of action

Suppresses absence-associated 3-Hz spike-and-wave activity.
The active metabolite N-desmethylmethsuximide blocks low-threshold T-type calcium channels, demonstrated in experimental thalamic neurons. This supports a proposed mechanism for antiabsence activity; its complete clinical mechanism is not established.
The active metabolite accumulates and contributes to clinical activity.

Pharmacology

Adult values unless specified. Vd/F denotes apparent oral distribution volume.

Pharmacokinetics

Bioavailability: Absolute bioavailability not quantified in the cited sources.
Elimination half-life: Parent methsuximide: mean 1.4 hours in a small 1979 study. Do not confuse this with its longer-lived active metabolite.
Volume of distribution: Not quantified in the cited sources.
Active metabolite(s): N-desmethylmethsuximide (active).
Active-metabolite half-life: N-desmethylmethsuximide: mean 38 hours in the 1979 study; elimination half-life 72.2 hours in the 1983 study.
Protein binding: Not quantified in the cited sources.
Metabolism / elimination: N-demethylation to active N-desmethylmethsuximide.

Estimates come from small, different patient populations and regimens; the active-metabolite values are not parent-drug half-lives.

Molecular structure

Principal compound; salt and product forms may differ.
NIH PubChem structure and record ↗

Product history

Initial U.S. approval: February 8, 1957 (NDA 010596)
Market / formulation history: Celontin and generic 300 mg capsules are listed in DailyMed; listing does not confirm current stock.
Brands: Celontin · generic capsules
Manufacturer / marketer: Parke-Davis / Pfizer (Celontin); ANI (representative generic)
Generic availability: Yes — a generic capsule label is listed in DailyMed.
Related drugs: Ethosuximide and phensuximide are other succinimides.

Sources & review status

The ANI label is a representative generic source. The Celontin brand-name package insert is linked separately; consult the exact product prescribed.

Brand reference: Celontin capsules ↗

Indications and DailyMed PDFs checked: 2026-09-26. Other profile sources reviewed: 2026-09-26 · label revision noted at that review: Celontin: March 2023; DailyMed updated April 7, 2026. This is a draft reference; final review is pending.

Methsuximide