ethosuximide (Zarontin)

Introduction

Tradename: Zarontin.

Indications

• absence (petit mal) seizures
• akinetic epilepsy

Dosage

• 250 mg PO QD if 3-6 years of age
• 500 mg PO QD > 6 years

Tabs: 250 mg.

Elixir: 250 mg/5 mL.

Monitor

• liver function tests periodically

• monitor with anticonvulsants

Adverse effects

• common (> 10%)
  • Stevens-Johnson syndrome, lupus-like syndrome, anorexia, ataxia, dizziness, drowsiness, hiccups, headache, nausea/vomiting, weight loss
• less common (1-10%)
  • aggressiveness, depression, nightmares, weakness, fatigue
• uncommon (< 1%)
  • agranulocytosis, leukopenia, aplastic anemia, thrombocytopenia, pancytopenia, paranoid psychosis, urticaria, exfoliative dermatitis
• other: ataxia

• drug adverse effects of anticonvulsants

Drug interactions

• agents which may increase ethosuximide metabolism
  • carbamazepine
  • phenytoin
  • primidone
  • phenobarbital
• valproic acid may increase or decrease ethosuximide levels
• ethosuximide induces cyt P450 3A4
  • may diminish levels of drugs metabolized by cyt P450 3A4
• isoniazid may inhibit hepatic metabolism of ethosuximide

• drug interaction(s) anticonvulsants with anti-bacterial agents
• drug interaction(s) anticonvulsants with statins

Test interactions

• may cause positive direct Coomb's test
• may increase ANA titer
• may increase serum AST

Laboratory

• specimen:
  • serum, plasma (heparin, EDTA)
  • collect at trough concentration
  • stable for several hours at room temperature
  • stable for 1 year at -20 degrees C
• methods: HPLC, GLC, EIA, FPIA
• labs with Loincs
  • ethosuximide in body fluid
    • ethosuximide in serum/plasma

More general terms

• succinimide
• anticonvulsant

Database

• PubChem: http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=3291
• PubChem: http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=551129