Tiagabine. A review of its pharmacodynamic and pharmacokinetic properties and therapeutic potential in the management of epilepsy.

Tiagabine is a gamma-aminobutyric acid (GABA) uptake inhibitor which is structurally related to nipecotic acid but has an improved ability to cross the blood-brain barrier. Clinical trials have shown that tiagabine is effective as add-on therapy in the management of patients with refractory partial epilepsy. In short term studies of this indication, tiagabine < or = 64 mg/day for 7 to 12 weeks reduced the complex partial and simple partial seizure frequency by > or = 50% in 8 to 31 and 28.2 to 37% of patients, respectively. Tiagabine appeared to produce a sustained reduction in seizure frequency in studies of up to 12 months' duration. Data from preliminary studies are currently insufficient to confirm the usefulness of tiagabine when used as monotherapy or in the treatment of children with epilepsy. Further studies are, therefore, necessary to more fully elucidate the efficacy of the drug in these settings. Adverse events associated with tiagabine are primarily CNS-related and include dizziness, asthenia, nonspecific nervousness and tremor. Skin rash or psychosis occurred with similar frequencies among tiagabine- and placebo-treated patients. With long term administration (> or = 1 year for many patients), the profile and incidence of adverse events was similar to that for short term therapy. Tiagabine does not appear to affect the hepatic metabolism of other drugs such as carbamazepine and phenytoin. Possible disadvantages of tiagabine include its short plasma elimination half-life, necessitating 2 to 4 times daily administration, and its inducible hepatic metabolism. Thus, tiagabine is a new antiepileptic agent with a novel mechanism of action, which has demonstrated efficacy in the adjunctive treatment of patients with refractory partial epilepsy. Further investigation of the efficacy of tiagabine is expected to provide a clearer definition of its place in the treatment of epilepsy and its relative merits in relation to other antiepileptic drugs.