Synonyms
- Zarontin®
Special Instructions
State other drugs taken by patient.
Expected Turnaround Time
1 - 3 days
Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.
Specimen Requirements
Specimen
Serum or plasma
Volume
1 mL
Minimum Volume
0.6 mL (Note: This volume does not allow for repeat testing.)
Container
Red-top tube, lavender-top (EDTA) tube, or green-top (heparin) tube. Do not use a gel-barrier tube. The use of gel-barrier tubes is not recommended due to slow absorption of the drug by the gel. Depending on the specimen volume and storage time, the decrease in drug level due to absorption may be clinically significant.
Collection
Transfer separated serum or plasma to a plastic transport tube. Oral: peak: two to four hours after dose; trough: immediately prior to next dose. Peak or trough levels may be used to monitor therapy because blood levels are fairly constant.
Storage Instructions
Room temperature
Stability Requirements
Temperature | Period |
|---|---|
Room temperature | 14 days |
Refrigerated | 14 days |
Frozen | 14 days |
Freeze/thaw cycles | Stable x3 |
Causes for Rejection
Gel-barrier tube; hemolysis; lipemia; gross bacterial contamination
Test Details
Use
Evaluate toxicity; monitor therapeutic levels
Methodology
Immunoassay (IA)
Reference Interval
Therapeutic: 40−100 μg/mL
Critical Value
Potentially toxic: >100 μg/mL
Additional Information
Ethosuximide is well absorbed orally, and the peak plasma concentration occurs in one to four hours. It is minimally bound to plasma protein and eliminated primarily via hepatic metabolism with 10% to 20% of the administered dose excreted unchanged in the urine. The half-life is variable but averages 52 to 56 hours in adults and 32 to 41 hours in children. Breast milk concentrations are slightly less than corresponding plasma concentrations, but problems related to breast-feeding in humans have not been documented. Control of absence seizures usually is achieved with plasma concentrations of 40−100 μg/mL, but concentrations up to 160 μg/mL may be required and are tolerated in some patients. As is the case with other antiepileptic drugs metabolized by the P450 enzyme system, co-administration of carbamazepine, phenytoin, phenobarbital, or primidone will result in decreased ethosuximide levels, whereas valproic acid can increase ethosuximide levels.1
Footnotes
1. Bourgeois BF. Pharmacokinetic properties of current antiepileptic drugs: What improvements are needed? Neurology. 2000; 55(Suppl 3):S11-S16. 11147563
References
American Medical Association, Division of Drugs and Toxicology. Drug Evaluations Subscription. Chicago, Ill: AMA; Fall 1992.
LOINC® Map
| Order Code | Order Code Name | Order Loinc | Result Code | Result Code Name | UofM | Result LOINC |
|---|---|---|---|---|---|---|
| 007443 | Ethosuximide (Zarontin), Serum | 3616-0 | 007443 | Ethosuximide (Zarontin), Serum | ug/mL | 3616-0 |
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