Dosing and uses of Zarontin (ethosuximide)
Adult dosage forms and strengths
capsule
- 250mg
syrup
- 250mg/5mL
Absence Seizures
500 PO qDay, increase by 250 mg q4-7d; generally not to exceed 1.5 g/day
Renal Impairment
Monitor closely
Hepatic Impairment
Monitor closely
Other Information
May take with food or milk
Therapeutic range: 40-100 mg/L (may require 4-7 days to reach steady state)
Pediatric dosage forms and strengths
capsule
- 250mg
syrup
- 250mg/5mL
Absence Seizures
<3 years: Safety and efficacy not established
3-6 years: 250 mg PO qDay initially; if needed, may increase by 250 mg q4-7d; usual maintenance dose 20 mg/kg/day
>6 years: As adults, 500 mg PO qDay initially; may increase by 250 mg q4-7d; generally not to exceed 1.5 g/day in divided doses
Other Information
Therapeutic range: 40-100 mg/L (may require 4-7 days to reach steady state)
May take with food or milk
Geriatric dosage forms and strengths
500 PO qDay, increase by 250 mg q4-7d; generally not to exceed 1.5 g/day
Zarontin (ethosuximide) adverse (side) effects
Freqency Not Defined
Common
- Dizziness
- Headache
- Somnolence
- Anorexia
- Diarrhea
- GI upset
- Nausea
- Vomiting
Less Common
- Ataxia, confusion, drowsiness, sleep disturbance
- Gum hypertrophy, hiccoughs, swelling of tongue
- Blood dyscrasias including aplastic anemia
- Allergic reaction
- Urticaria
- Pruritic erythematous rashes
- Blurred vision, myopia
Rare
- Psychosis
- Seizure
- Suicidal thoughts and behavior
- Stevens-Johnson syndrome
- Systemic lupus erythematosus
- Hirsutism
Warnings
Contraindications
Hypersensitivity
Cautions
Do not discontinue rapidly; proceed slowly when increasing or decreasing dosage, as well as when adding or eliminating other medications; abrupt withdrawal of anticonvulsant medication may precipitate absence (petit mal) status
When used alone in mixed types of epilepsy, therapy may increase frequency of grand mal seizures in some patients
Blood dyscrasias may occur; perform periodic blood counts; should signs and/or symptoms of infection (e.g., sore throat, fever) develop, consider blood counts
Systemic lupus erythematosus reported
May cause CNS depression
Antiepileptic drugs increase risk of suicidal thoughts or behavior in patients taking these drugs for any indication; monitor for the emergence or worsening of depression, suicidal thoughts or behavior, and/or any unusual changes in mood or behavior
May potentiate effect of other sedatives
Serious dermatologic reactions reported including Stevens Johnson syndrome (SJS); onset usually within 28 days, but can occur later; discontinue therapy at first sign of rash, unless rash is clearly not drug-related; if signs or symptoms suggest SJS, use of this drug should not be resumed; consider alternative therapy
Drug reaction with Eosinophilia and Systemic Symptoms (DRESS), also known as multi organ hypersensitivity, reported; some fatal or life-threatening; early manifestations of hypersensitivity (e.g. fever, lymphadenopathy) may be present even though rash is not evident; if such signs or symptoms appear, the patient should be evaluated immediately and therapy discontinued if an alternative etiology for the signs or symptoms cannot be established
Abnormal renal and hepatic function studies reported; administer with extreme caution to patients with known liver or renal disease; periodic urinalysis and liver function studies recommended for all patients receiving the drug
Pregnancy and lactation
Pregnancy category: C
Lactation: enters breast milk; use with caution (AAP Committee states "compatible with nursing")
Pregnancy Registry: Pregnant women exposed to ethosuximide are encouraged to enroll themselves by calling 1-888-233-2334.
Pregnancy categories
A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.
B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.
C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.
D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.
X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.
NA: Information not available.
Pharmacology of Zarontin (ethosuximide)
Mechanism of action
Succinimide; depresses nerve transmission in motor cortex, increases convulsive stimuli threshold in CNs
Pharmacokinetics
Peak Plasma Time: 4 hr
Protein bound: Low
Metabolism: liver (hydroxylation, glucuronidation)
Excretion: Mainly renal, some bile
Half-life
- Children: 30 hr
- Adults: 60 hr
