Dose-dependent pharmacokinetics and brain penetration of rufinamide following intravenous and oral administration to rats

Rufinamide is a third-generation antiepileptic drug, approved recently as an orphan drug for the treatment of Lennox–Gastaut syndrome. Although extensive research was conducted, its pharmacokinetics in rats was not described. This work addresses that area by describing in a rapid pharmacokinetic study the main pharmacokinetic properties of rufinamide at three different doses of 1 mg/kg body weight (bw), 5 mg/kg bw, and 20 mg/kg bw. Furthermore, total brain concentrations of the drug were determined in order to characterize its brain-to-plasma partition coefficient. Adult Wistar male rats, weighing 200–450 g, were administered rufinamide by intravenous and oral routes. Rufinamide concentrations from plasma samples and brain tissue homogenate were determined using a liquid chromatography–mass spectrometric method and pharmacokinetic parameters were calculated. The mean half-life was between 7 and 13 h, depending on route of administration – intravenously administered drug was eliminated faster than orally administered drug. Mean (S.E.M.) total plasma clearance was 84.01 ± 3.80 ml/h/kg for intravenous administration, while the apparent plasma clearance for oral administration was 95.52 ± 39.45 ml/h/kg. The mean (S.E.M.) maximum plasma concentration reached after oral administration of 1 mg/kg bw and 5 mg/kg bw was 0.89 ± 0.09 μg/ml and 3.188 ± 0.71 μg/ml, respectively. The median (range) time to reach maximum plasma concentration (tmax) was 4 (2–8) h. Mean (S.E.M.) brain-to-plasma concentration ratio of rufinamide was 0.514 ± 0.036, consistent with the brain-to-plasma ratio calculated from the area under curves (AUC0−t) of 0.441 ± 0.047. No influence of dose, route of administration, or post-dosing time was observed on brain-to-plasma ratio.

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