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22928 Topiramate, Serum (TOPI)

Topiramate, Serum (TOPI)
Test Code: TOPIRSO
Synonyms/Keywords
Topamax (Topiramate), Topiramate (Topamax)
Useful For
Monitoring serum concentrations of topiramate
 
Assessing compliance
 
Assessing potential toxicity​
Specimen Requirements
Specimen Type Preferred Container/Tube Acceptable Container/Tube Specimen Volume Specimen Minimum Volume
(allows for 1 repeat)
Pediatric Minimum Volume
(no repeat)
Serum​ ​Red Top Tube (RTT) ​1 mL ​0.5 mL
Collection Processing Instructions
​Submit specimen in a plastic vial
Specimen Stability Information
Specimen Type Temperature Time
​Serum ​ ​ ​Frozen ​28 days
​Refrigerated (preferred) ​28 days
​Ambient ​28 days
Interference

​This test cannot be performed on whole blood.

Performing Laboratory Information
Performing Location Day(s) Test Performed Report Available
Methodology/Instrumentation
​Mayo Clinic Laboratories Monday through Saturday​ ​1-2 days
Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)
Reference Lab
Test 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 renal 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 renal 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.

Reference Range Information
Performing Location Reference Range
​Mayo Clinic Laboratories
Depends on clinical use:
 
Anticonvulsant: 5.0-20.0 mcg/mL
Psychiatric: 2.0-8.0 mcg/mL
Interpretation

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 drawn at trough (ie, immediately before the next dose).

Toxic levels have not been well established.

Outreach CPTs
CPT Modifier
(if needed)
Quantity Description Comments
​80201
Synonyms/Keywords
Topamax (Topiramate), Topiramate (Topamax)
Ordering Applications
Ordering Application Description
​COM
​Topiramate, Serum (TOPI​)
​Cerner ​Topiramate, Serum (TOPI)
If the ordering application you are looking for is not listed, contact your local laboratory for assistance.
Specimen Requirements
Specimen Type Preferred Container/Tube Acceptable Container/Tube Specimen Volume Specimen Minimum Volume
(allows for 1 repeat)
Pediatric Minimum Volume
(no repeat)
Serum​ ​Red Top Tube (RTT) ​1 mL ​0.5 mL
Collection Processing
​Submit specimen in a plastic vial
Specimen Stability Information
Specimen Type Temperature Time
​Serum ​ ​ ​Frozen ​28 days
​Refrigerated (preferred) ​28 days
​Ambient ​28 days
Interference

​This test cannot be performed on whole blood.

Useful For
Monitoring serum concentrations of topiramate
 
Assessing compliance
 
Assessing potential toxicity​
Reference Range Information
Performing Location Reference Range
​Mayo Clinic Laboratories
Depends on clinical use:
 
Anticonvulsant: 5.0-20.0 mcg/mL
Psychiatric: 2.0-8.0 mcg/mL
Interpretation

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 drawn at trough (ie, immediately before the next dose).

Toxic levels have not been well established.

For more information visit:
Performing Laboratory Information
Performing Location Day(s) Test Performed Report Available
Methodology/Instrumentation
​Mayo Clinic Laboratories Monday through Saturday​ ​1-2 days
Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)
Reference Lab
For billing questions, see Contacts
Outreach CPTs
CPT Modifier
(if needed)
Quantity Description Comments
​80201
For most current information refer to the Marshfield Laboratory online reference manual.