|Clinical Use:||To check compliance and for assessing potential toxicity.|
|Background:||Testing for topiramate is used by clinicians to monitor serum concentrations of topiramate, particularly in patients with renal disease or those co- administered phenytoin or carbamazepine. Topiramate is a broad spectrum, anti-epileptic drug used to control various types of seizures, Lennox-Gastaut syndrome (a type of childhood onset epilepsy), and migraine prophylaxis. Topiramate blocks sodium channels, potentiates gamma-aminobutyric acid (GABA) activity, and inhibits potentiation of the glutamate receptor, allowing the drug to block seizure spread. Topiramate shows favourable pharmacokinetics, with good absorption, low protein binding, and minimal metabolism. Elimination is predominantly renal as unaltered topiramate, with an elimination half-life of 20 to 30 hours.
Serum concentrations of other anticonvulsant drugs are not significantly affected by the concurrent administration of topiramate, with exception in individual patients on phenytoin exhibiting increased phenytoin plasma concentrations after addition of topiramate. Co-administration of phenytoin or carbamazepine decreases topiramate serum concentrations. Changes in co-therapy with phenytoin or carbamazepine for patients stabilized on topiramate therapy may require dose adjustment due to these instructions; therapeutic drug monitoring can assist this. As with other renally eliminated anticonvulsant drugs, patients with impaired renal function exhibit decreased topiramate clearance.
|Reference Ranges:||6 – 74 µmol/L|
|Patient Preparation:||None required|
|Specimen Requirements:||Serum (SST) sample|
|Turnaround Time:||1 week|
|Referred Test:||Referred test|
|Location:||Therapeutic Drug Monitoring Unit|