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Gabitril®
Diagnosis & Treatment > Seizure Medications > Gabitril® > Clinical pharmacology of Gabitril
 

Clinical pharmacology of Gabitril

Absorption
Gabitril is quickly and almost completely absorbed. Oral bioavailability is approximately 90% and absorption is linear over the therapeutic dosage range. Maximum serum concentrations are attained within 45 to 90 minutes in the fasting state and after a mean of 2.6 hours when taken with food. The extent of absorption is not affected by food.

Distribution and metabolism
Gabitril is extensively oxidized in the liver by isoform 3A of cytochrome P450. Only 2% of the administered dose is excreted as parent drug. The elimination of Gabitril is linear over the therapeutic dosage range.

The half-life is 5 to 8 hours in patients with uninduced liver function and 2 to 3 hours in patients taking hepatic enzyme–inducing AEDs. More frequent dosing does not appear to be necessary to compensate for the shortened half-life, however. The common maintenance dosage of 32 mg/day as add-on therapy is equally effective whether given as 16 mg twice daily or 8 mg four times daily.

Renal impairment does not change the pharmacokinetics of Gabitril. The half-life is increased to 12 to 16 hours in patients with hepatic impairment, however, requiring dosage reductions and less frequent dosing intervals.

Because Gabitril is metabolized in the liver, people with liver disease should be treated with caution. They may have to be started at a lower dose and have their dosage increased more slowly.

Steady state
Steady state is reached after 2 days of taking a stable dose of Gabitril. The dosage should not be increased until steady state has been reached (or some time later), so that the effects of the previous dosage can be assessed.