Classifications: central nervous system agent; anticonvulsant succinimide
Prototype: Ethosuximide
Pregnancy Category: D


500 mg capsules


Succinimide derivative reportedly less potent and less effective than other drugs of this class. Reduces the frequency of epileptiform attacks.

Therapeutic Effects

Apparently depresses the motor cortex and elevates the threshold of CNS sensitivity to seizure activity, thus lessening the incidence of seizure activity.


Management of petit mal epilepsy (absence seizures) and with other anticonvulsants when other forms of epilepsy coexist with petit mal.


Intermittent porphyria; liver or kidney disease; pregnancy (category D), lactation.

Route & Dosage

Absence Seizures
Adult/Child: PO 0.5–1 g b.i.d. or t.i.d.



Adverse Effects (1%)

Body as a Whole: Drowsiness, dizziness, ataxia, muscle weakness, flushing, periorbital edema, GI: Anorexia, nausea, vomiting. Urogenital: Reversible nephropathy. Hematologic: Granulocytopenia. Skin: Alopecia, pruritus, skin rash.


Drug: Carbamazepine decreases phensuximide levels; isoniazid significantly increases phensuximide levels; levels of both phenobarbital and phensuximide may be altered with increased seizure frequency.


Absorption: Readily absorbed from GI tract. Peak: 1–4 h. Metabolism: Metabolized in liver. Elimination: Excreted slowly in urine; small amounts excreted in bile and feces. Half-Life: 5–12 h.

Nursing Implications

Assessment & Drug Effects

Patient & Family Education

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug