Tiagabine
Tiagabine (Gabitril) is is a selective blocker of gamma-aminobutyric acid (GABA) uptake into presynaptic neurons. It is usually prescribed in combination with another antiepileptic drug for adults and children 12 years and older with partial seizures.
Tiagabine reaches peak serum concentration approximately 45 minutes following an oral dose in the fasting state. It is almost completely protein bound in plasma. Tiagabine has an elimination half-life of 7 to 9 hours. Concomitant use of phenytoin, phenobarbital, or carbamazepine may shorten the half life to 4 to 7 hours. Steady-state is achieved within 2 days. Tiagabine is metabolized by cytochrome P450 CYP3A.
Routine drug monitoring is usually not necessary . Therapeutic drug monitoring is indicated when tiagabine is combined with another antiepileptic drug that induces hepatic enzymes and when a patient does not respond to treatment.
Trough therapeutic range is 20-200 ng/mL when measured by liquid chromatography-tandem mass spectrometry. Serum concentrations >800 ng/mL indicates excessive dosing associated with adverse effects such as asthenia, ataxia, difficulty concentrating, and depression.
