Ethosuximide, Serum or Plasma

CPT: 80168
Print Share

Test Details

Synonyms

  • Zarontin®

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

Specimen Requirements

Specimen

Serum or plasma

Volume

1 mL

Minimum Volume

0.6 mL

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

Clinical Information

Special Instructions

State other drugs taken by patient.

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
Reflex Table for Ethosuximide (Zarontin), Serum
Order Code Order Name Result Code Result Name UofM Result LOINC
Reflex 1 007000 See below: 007000 See below: N/A

For Providers

Please login to order a test.

 

© 2017  Laboratory Corporation of America® Holdings and Lexi-Comp Inc. All Rights Reserved.

CPT Statement/Profile Statement

The LOINC® codes are copyright © 1994-2017, Regenstrief Institute, Inc. and the Logical Observation Identifiers Names and Codes (LOINC) Committee. Permission is granted in perpetuity, without payment of license fees or royalties, to use, copy, or distribute the LOINC® codes for any commercial or non-commercial purpose, subject to the terms under the license agreement found at https://loinc.org/license/. Additional information regarding LOINC® codes can be found at LOINC.org, including the LOINC Manual, which can be downloaded at LOINC.org/downloads/files/LOINCManual.pdf