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ethosuximide (Zarontin)
Tradename: Zarontin.
Indications:
1) absence (petit mal) seizures
2) akinetic epilepsy
Dosage:
1) 250 mg PO QD if 3-6 years of age
2) 500 mg PO QD > 6 years
Tabs: 250 mg.
Elixir: 250 mg/5 mL.
Monitor:
- liver function tests periodically [6]
Adverse effects:
1) common (> 10%)
- Stevens-Johnson syndrome, lupus-like syndrome, anorexia, ataxia, dizziness, drowsiness, hiccups, headache, nausea/vomiting, weight loss
2) less common (1-10%)
- aggressiveness, depression, nightmares, weakness, fatigue
3) uncommon (< 1%)
- agranulocytosis, leukopenia, aplastic anemia, thrombocytopenia, pancytopenia, paranoid psychosis, urticaria, exfoliative dermatitis
4) other: ataxia
Drug interactions:
1) agents which may increase ethosuximide metabolism
a) carbamazepine
b) phenytoin
c) primidone
d) phenobarbital
2) valproic acid may increase or decrease ethosuximide levels
3) ethosuximide induces cyt P450 3A4
-> may diminish levels of drugs metabolized by cyt P450 3A4
4) isoniazid may inhibit hepatic metabolism of ethosuximide
Test interactions:
1) may cause positive direct Coomb's test
2) may increase ANA titer
3) may increase serum AST
Laboratory:
1) specimen:
a) serum, plasma (heparin, EDTA)
b) collect at trough concentration
c) stable for several hours at room temperature
d) stable for 1 year at -20 degrees C
2) methods: HPLC, GLC, EIA, FPIA
3) labs with Loincs
- ethosuximide in body fluid
- ethosuximide in serum/plasma
Interactions
drug interactions
drug adverse effects of anticonvulsants
monitor with anticonvulsants
General
anticonvulsant
succinimide
Properties
COMPARTMENT:
mitochondrial matrix
MISC-INFO: elimination route LIVER
KIDNEY
1/2life 24-72 HOURS
30-50 HOURS
therapeutic-range 40-100 UG/ML
toxic-range >150 UG/ML
protein-binding <5%
elimination by hemodialysis +
pregnancy-category C
safety in lactation ?
Database Correlations
PUBCHEM correlations
References
- The Pharmacological Basis of Therapeutics, 9th ed.
Gilman et al, eds. Permagon Press/McGraw Hill, 1996
- Harrison's Principles of Internal Medicine, 13th ed.
Companion Handbook. Isselbacher et al (eds),
McGraw-Hill Inc. NY, 1995, pg 701
- Kaiser Permanente Northern California Regional Drug
Formulary, 1998
- Clinical Guide to Laboratory Tests, 3rd ed. Teitz ed.,
W.B. Saunders, 1995
- Medical Knowledge Self Assessment Program (MKSAP) 15,
American College of Physicians, Philadelphia 2009
- Prescriber's Letter 17(7): 2010
Recommended Lab Monitoring for Common Medications
Liver Function Test Scheduling
Detail-Document#: 260704
(subscription needed) http://www.prescribersletter.com