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Test Code ETX Ethosuximide, Serum


Specimen Required


Supplies: Sarstedt Aliquot Tube, 5 mL (T914)

Collection Container/Tube:

Preferred: Serum gel

Acceptable: Red top

Submission Container/Tube: Plastic vial

Specimen Volume: 0.5 mL

Collection Instructions:

1. Serum gel tubes should be centrifuged within 2 hours of collection.

2. Red-top tubes should be centrifuged and the serum aliquoted into a plastic vial within 2 hours of collection.


Secondary ID

8769

Useful For

Monitoring ethosuximide therapy

 

Determining compliance

 

Assessing ethosuximide toxicity

Method Name

Enzyme-Multiplied Immunoassay Technique (EMIT)

Reporting Name

Ethosuximide, S

Specimen Type

Serum

Specimen Minimum Volume

0.25 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Serum Refrigerated (preferred) 14 days
  Frozen  28 days
  Ambient  14 days

Reject Due To

Gross hemolysis Reject

Clinical Information

Ethosuximide (Zarontin) is used in the treatment of absence (petit mal) epilepsy in adults and children 3 years and older. Ethosuximide is almost completely absorbed from the gastrointestinal tract, reaching a peak plasma concentration in 1 to 4 hours following oral administration.

 

Approximately 10% to 20% of the drug is excreted unchanged in the urine; the remainder is metabolized by hepatic microsomal enzymes. The volume of distribution of ethosuximide is approximately 0.7 L/kg, and its half-life is 17 to 56 hours (adult) and 30 hours (pediatric). Minimal ethosuximide circulating in the blood is bound to protein (approximately 22%).

 

Ethosuximide produces a barbiturate-like toxicity, characterized by central nervous system and respiratory depression, nausea, and vomiting, when the blood level is greater than 120 mcg/mL.

Reference Values

Therapeutic: 40-100 mcg/mL

Critical value: >150 mcg/mL

Interpretation

Dosage is guided by blood levels; the therapeutic range for ethosuximide is 40 to 100 mcg/mL.

 

Toxic concentration: above 120 mcg/mL.

CPT Code Information

80168

LOINC Code Information

Test ID Test Order Name Order LOINC Value
ETX Ethosuximide, S 3616-0

 

Result ID Test Result Name Result LOINC Value
8769 Ethosuximide, S 3616-0

Forms

If not ordering electronically, complete, print, and send 1 of the following forms with the specimen:

-Therapeutics Test Request (T831)

-Neurology Specialty Testing Client Test Request (T732)