Frisium, Norclobazam, Onfi, Clobazam and Metabolite, Serum (CLOBZ), CLOBZSO
Monitoring clobazam therapy
Draw blood immediately before next scheduled dose.
Centrifuge and aliquot serum into plastic vial within 2 hours of collection.
Additional Information: Trough specimens are recommended as therapeutic ranges are based on specimens collected at trough (ie, immediately before the next dose).
Clobazam is a broad spectrum, antiepileptic drug used for various types of seizures, Lennox-Gastaut syndrome (a type of childhood onset epilepsy), and migraine prophylaxis. Clobazam 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, all of which contribute to its antiepileptic and antimigraine efficacy.
In general, clobazam 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 kidney function exhibit decreased clobazam clearance and a prolonged elimination half-life.
Serum concentrations of other anticonvulsant drugs are not significantly affected by the concurrent administration of clobazam, with the exception of patients on phenytoin whose serum concentrations can increase after the addition of clobazam. Other drug-drug interactions include the coadministration of phenobarbital, phenytoin, or carbamazepine, which can result in decreased clobazam concentrations. In addition, concurrent use of posaconazole and clobazam may result in the elevation of clobazam serum concentrations. Therefore, changes in cotherapy with these medications (phenytoin, carbamazepine, posaconazole, or phenobarbital) may require dose adjustment of clobazam, and therapeutic drug monitoring can be helpful. The most common adverse drug effects associated with clobazam include weight loss, loss of appetite, somnolence, dizziness, coordination problems, memory impairment, and paresthesia.
Therapeutic Range: 30-300 ng/mL
Therapeutic Range: 300-3,000 ng/mL
The results of this test should be interpreted in conjunction with the patient's physical signs, symptoms, and other laboratory test results.
Most individuals display optimal response to clobazam when serum levels of clobazam are between 30 and 300 ng/mL and N-desmethylclobazam are between 300 and 3000 ng/mL. Risk of toxicity is increased when clobazam levels are above 500 ng/mL or N-desmethlyclobazam levels are above 5000 ng/mL.
Some individuals may respond well outside of these ranges or may display toxicity within the therapeutic range; thus, interpretation should include clinical evaluation.