Pharmacokinetics of the monohydroxy derivative of oxcarbazepine and its enantiomers after a single intravenous dose given as racemate compared with a single oral dose of oxcarbazepine.

Oxcarbazepine (OXC) is an antiepileptic drug. In humans, OXC is metabolized via reduction and conjugation. Monohydroxy derivative of OXC (MHD) is the major pharmacologically active component after OXC ingestion. This study was performed to characterize the disposition of the two enantiomers of MHD after oral and intravenous administration and to estimate the bioavailability of MHD after a single oral dose administration of OXC compared to a single intravenous administration of MHD. The study was performed in two parts. In a first pilot study, three intravenous doses were given in an ascending manner (150, 200, and 250 mg of MHD; one subject per dose level) to assess the safety, tolerability, and basic pharmacokinetics. Part two was an open, single-center, randomized, two-way crossover, single-dose trial in 12 healthy adult subjects (n = 6 males and n = 6 females) given OXC orally (one film-coated 300-mg tablet of OXC) and MHD intravenously (250 mg infused over 30 min). Concentrations of OXC and its metabolites were measured by means of high-performance liquid chromatography methods. OXC given as a tablet is completely absorbed in man under fasting conditions. When MHD is given intravenously, (S)-MHD predominates as free compound in plasma. When OXC is administered orally, the ratio of the area-under-the-curve values of (S)-MHD over (R)-MHD equals 3.8, indicating an enantioselective reduction of the prochiral carbonyl group of OXC.