Summary: Purpose:In two open-label long-term safety studies, we determined tiagabine (TGB) pharmacokinetics in patients with epilepsy.
Methods:In all, 2,147 plasma samples from 5 1 1 patients who participated in the studies were available. The total daily dose ranged from 2 mg administered once daily to 80 mg administered in four doses. A one-compartment model with first-order absorption and elimination was used to fit the TGB plasma concentration-time data, with a population pharmacokinetic approach.Results TGB was rapidly absorbed after oral administration in healthy subjects, with maximum plasma concentrations generally occurring S1 h after dosing (1). After singleand multiple-dose administration of 2-24 mg TGB, dosenormalized peak plasma concentrations and area under the plasma concentration-time curve values appeared to be independent of dose with an overall mean clearance (CLR) of -9 Lh. The apparent half-life (t%) was quite variable, averaging -5-8 h (1).In patients with epilepsy who had been treated with other antiepileptic drugs (AEDs) known to induce hepatic metabolism enzymes [carbamazepine (CBZ) phenytoin (PHT) phenobarbital (PB), primidone], TGB clearance values were significantly increased (29.2 L h ) relative to those of patients receiving no additional drugs or drugs that do not induce the hepatic liver enzymes (8.2 LA), such as valproate (VPA) (2,3).To assess further the safety and tolerability of TGB, two long-term studies were initiated (4). The patient population selected for the first study included patients who had received study medication in a prior trial of TGB as add-on or monotherapy for partial seizures. The patient population selected for the second study included patients with a diagnosis of any kind of epilepsy. In the present analysis, we characterized and studied the effect of different covariates on TGB pharmacokinetics in patients with epilepsy.
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