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EPIC CODE: LAB498 Topiramate, Serum

Additional Codes

Sunquest:   TOPIRM
Mayo:          TOPI
Previously:  ARUP 0070390

Reporting Name

Topiramate, S

Useful For

Monitoring serum concentrations of topiramate


Assessing compliance


Assessing potential toxicity

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Specimen Type

Serum Red

Specimen Required

Collection Container/Tube: Red top (serum gel/SST are not acceptable)

Submission Container/Tube: Plastic vial

Specimen Volume: 1 mL

Collection Instructions:

1. Draw blood immediately before next scheduled dose.

2. Centrifuge and aliquot serum into plastic vial; within 2 hours of collection.

Specimen Minimum Volume

0.5 mL

Specimen Stability Information

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

Reference Values

Anticonvulsant: 5.0-20.0 mcg/mL

Day(s) Performed

Monday through Friday

Test Classification

This test was developed, and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
TOPI Topiramate, S 17713-9


Result ID Test Result Name Result LOINC Value
81546 Topiramate, S 17713-9

Clinical Information

Topiramate is a broad spectrum, antiepileptic drug used for various types of seizures, Lennox-Gastaut syndrome (a type of childhood onset epilepsy), and migraine prophylaxis. Topiramate blocks voltage-dependent sodium channels, potentiates gamma-aminobutyric acid (GABA) activity at some of the GABA receptors, and inhibits potentiation of the glutamate receptor and carbonic anhydrase enzyme, which all contribute to its antiepileptic and antimigraine efficacy.


In general, topiramate shows favorable pharmacokinetics with good absorption (1-4 hours for the immediate-release formulation), low protein binding, and minimal hepatic metabolism. Elimination is predominantly via the kidney, and it is excreted unchanged in the urine with an elimination half-life of approximately 21 hours. As with other anticonvulsant drugs eliminated by the renal system, patients with impaired kidney function exhibit decreased topiramate clearance and a prolonged elimination half-life.


Serum concentrations of other anticonvulsant drugs are not significantly affected by the concurrent administration of topiramate, with the exception of patients on phenytoin whose serum concentrations can increase after the addition of topiramate. Other drug-drug interactions include the coadministration of phenobarbital, phenytoin, or carbamazepine, which can result in decreased topiramate concentrations. In addition, concurrent use of posaconazole and topiramate may result in the elevation of topiramate serum concentrations. Therefore, changes in cotherapy with these medications (phenytoin, carbamazepine, posaconazole, or phenobarbital) may require dose adjustment of topiramate, and therapeutic drug monitoring could assist with this. The most common adverse drug effects associated with topiramate include weight loss, loss of appetite, somnolence, dizziness, coordination problems, memory impairment, and paresthesia.


Most individuals display optimal response to topiramate with serum levels 5.0 to 20.0 mcg/mL when used to control seizures. Some individuals may respond well outside of this range or may display toxicity within the therapeutic range; thus, interpretation should include clinical evaluation.


Therapeutic ranges are based on specimens collected at trough (ie, immediately before the next dose).


Toxic levels have not been well established.


This test cannot be performed on whole blood.

Clinical Reference

1. Hiemke C, Baumann P, Bergemann N, et al: AGNP consensus guidelines for therapeutic drug monitoring in psychiatry: Update 2011. Pharmacopsychiatry. 2011 Sept;44(6):195-235

2. Patsalos PN, Berry DJ, Bourgeois BF, et al: Antiepileptic drugs-best practice guidelines for therapeutic drug monitoring: a position paper by the subcommission on therapeutic drug monitoring, ILAE Commission on Therapeutic Strategies. Epilepsia. 2008 Jul;49(7):1239-1276

3. Johannessen SI, Tomsom T: Pharmacokinetic variability of newer antiepileptic drugs: when is monitoring needed? Clin Pharmacokinet. 2006;45(11):1061-1075

4. Rifai N, Horvath AR, Wittwer CT, eds: Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 6th ed. Elsevier; 2018

Method Description

Samples are diluted and extracted online by liquid chromatography, with detection by tandem mass spectrometry.(Unpublished Mayo method)

Report Available

1 to 2 days

Specimen Retention Time

14 days

Reject Due To

Gross hemolysis OK
Gross lipemia OK
Gross icterus OK

NY State Approved


Secondary ID



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

-Neurology Specialty Testing Client Test Request (T732)

-Therapeutics Test Request (T831)

Carle Health System Greater Peoria Region Additional Information:


  • Tompamax Concentration
  • Tompamax Level
  • Topamax
  • Topiramate Concentration
  • Topiramate Level