Section 01 · Monograph
Methsuximide
Reviewed Nov 2026FDA label
CelontinT-type Ca2+ blocker
- Forms
- Cap: 150, 300mg
- Dose
- 600-1200mg/day divided
- MOA
- Blocks thalamic T-type Ca2+ channels
Indications
- Control of absence (petit mal) seizures refractory to other anticonvulsantsFDA-labeled
Mechanism of Action
- Succinimide anticonvulsant; presumed mechanism similar to ethosuximide — reduces T-type calcium currents in thalamocortical neurons, suppressing the spike-and-wave discharges characteristic of absence seizures
- Also raises seizure threshold and depresses motor cortex excitability
Full Dosing
Adult / usual
- Dosing must be individualized to the lowest effective dose
Pediatric
- Adults and children: initiate 300mg/day, increase by 300mg/day at weekly intervals as needed and tolerated, up to a maximum of 1.2g/day in divided doses
Contraindications
- Known hypersensitivity to methsuximide or other succinimides
Drug Interactions
- May increase plasma concentrations of concurrently administered phenytoin and phenobarbital — periodic monitoring of anticonvulsant levels recommended
- Additive CNS depression with other sedating agents
Adverse Effects
- Common: drowsiness, ataxia, dizziness, headache, blurred vision, nausea/vomiting, hiccups
- Hematologic: leukopenia, eosinophilia, and rare pancytopenia/agranulocytosis
- Psychiatric: irritability, confusion, rare psychotic behavior; suicidal ideation (class effect of AEDs)
- Dermatologic: rash, rare Stevens-Johnson syndrome
- Renal: proteinuria reported
Monitoring Parameters
- Periodic CBC given risk of blood dyscrasias
- Periodic liver and renal function testing
- Screen for mood changes/suicidal ideation
- Serum levels of concomitant phenytoin/phenobarbital if co-administered
Pregnancy & Lactation
- Limited human data; use only if benefit outweighs risk. Enrollment in the North American Antiepileptic Drug (NAAED) Pregnancy Registry encouraged (1-888-233-2334)
- Unknown whether excreted in breast milk; weigh risks/benefits of breastfeeding