Methsuximide (Celontin, Pfizer)
Methsuximide (Celontin) is an old antiepileptic drug, typically used as a third-string agent when other drugs have failed. It recently was withdrawn from the market because of low usage rates, but some individuals still have and take a supply.
It is chemically related to ethosuximide (Zarontin), but has a different profile of action. Celontin is a broad-spectrum drug, with actions against partial seizures and absence (petit mal) seizures.
Summary Data for Methsuximide
Pill sizes: 150, 300 mg (yellow) capsules.
Liquid for oral: none.
Injectable: none.
Typical adult dose:
Initial 150-300 mg/d, increased over a few weeks to a target dose of 300 - 1,200 mg/d in 1-2 divided doses.
Typical pediatric dose: Start with 150 mg/d, increased over a few weeks to a target of 150-1,200 mg/d in 1-2 divided doses.
Metabolism: liver metabolism via the CYP 2C9 system to the active metabolite, N-desmethylmethsuximide (NDM).
Half-life: The NDM metabolite has a half-life of 24-72 hours.
Serum levels: 10-40 mcg/ml of the NDM metabolite.
Pregnancy: Category C - can cause birth defects in animals, unknown in humans.
Drugs that raise MSM levels: Dilantin, phenobarbital, Felbatol.
Drugs that lower MSM levels: Tegretol (but increases the epoxide metabolite)
MSM increases effects of: Dilantin, phenobarbital, carbamazepine epoxide
MSM decreases effects of other drugs:
Dangerous Side Effects
Rare blood count problems.
Common Side Effects
GI upset, dizziness, sleepiness, headache.
Other Side Effects
Behavior changes, irritability, skin rash, hiccups.