Topiramate, Serum or Plasma

CPT: 80201
Updated on 1/24/2018
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Test Details

Synonyms

  • Topamax®

Methodology

Liquid chromatography/tandem mass spectrometry (LC/MS-MS)

Reference Interval

Therapeutic: 2.0−25.0 μg/mL

Additional Information

Topiramate is an anticonvulsant drug used as an adjunctive therapy in the treatment of patients with partial and secondary generalized epilepsy. Topiramate is a sulfamate-substituted monosaccharide, derived from D-fructose. The animal models suggest that topiramate exerts its anticonvulsant effect primarily by blocking the spread of seizures, rather than by elevating the seizure threshold. Pharmacokinetic studies in humans have shown that topiramate is absorbed rapidly, excreted largely unchanged in the urine.1 Carbamazepine and phenytoin can significantly induce the metabolism of topiramate, whereas valproic acid has only a slight influence on topiramate concentrations.2 The elimination half-life of topiramate is 18 to 23 hours and is dose-dependent; however, children, as differentiated from adults, can require at least a twofold increase in dose to achieve a comparable plasma level.3 The drug is approximately 15% protein bound. Although carbamazepine and phenytoin induce the metabolism of topiramate and shorten its half-life, topiramate has no significant effect on the plasma concentrations of these drugs or valproic acid. Maintenance doses of topiramate, given twice daily, range from 300−600 mg/day. Side effects include dizziness, reduced cognitive function, weight loss, and headache. As observed with many therapeutic agents, the interpatient variability in clinical response at similar topiramate plasma concentration can be appreciable. Differences in plasma levels between responders, nonresponders, and seizure-free patients can be indiscernible.

Specimen Requirements

Specimen

Serum or plasma

Volume

1 mL

Minimum Volume

0.3 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.

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

Clinical Information

Footnotes

1. Reife RA. Topiramate: A novel antiepileptic agent. In: Shorvan SD, et al, eds. The Treatment of Epilepsy. Cambridge, Mass: Blackwell Science;1996:chap 38.
2. May TW, Rambeck B, Jürgens U. Serum concentrations of topiramate in patients with epilepsy: Influence of dose age, and comedication. Ther Drug Monit. 2002 Jun; 24(3):366-374. 12021627
3. Ferrari AR, Guerrini R, Gatti G, Alessandri MG, Bonanni P, Perucca E. Influence of dosage, age, and comedication on plasma topiramate concentrations in children and adults with severe epilepsy and preliminary observations on correlations with clinical response. Ther Drug Monit. 2003 Dec; 25(6):700-708. 14639056

References

Bourgeois BF. Pharmacokinetic properties of current antiepileptic drugs. What improvements are needed? Neurology. 2000; 55(11 Suppl 3):S11-16. 11147563
Innofluor Topiramate Assay System [package insert] Oxis International;1997.
Rosenfeld WE, Liao S, Kramer LD, et al. Comparison of the steady-state pharmacokinetics of topiramate and valproate in patients with epilepsy during monotherapy and concomitant therapy. Epilepsia. 1997 Mar; 38(3):324-333. 9070595

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
716285 Topiramate (Topamax), Serum 17713-9 716288 Topiramate, Serum ug/mL 17713-9

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