The Influence of Gender and Food on the Pharmacokinetics of Sodium Oxybate Oral Solution in Healthy Subjects

Sodium oxybate (Xyrem®; gamma-hydroxybutyrate) oral solution was recently approved in the United States for the treatment of cataplexy in patients with narcolepsy. Two single-center, randomized, open-label studies in healthy volunteers receiving single oral 4.5-g doses of sodium oxybate evaluated effects of (1) gender on oxybate pharmacokinetics and (2) food on its oral bioavailability. In the latter study, one dose was administered after an overnight fast, another after a high-fat meal; 1 week separated treatments. Sodium oxybate pharmacokinetics was not significantly different between sexes. However, food significantly altered the bioavailability of oxybate by decreasing mean peak plasma concentration, increasing median time-to-peak concentration, and decreasing the area under the plasma concentration-time curve. Food did not affect elimination and urinary excretion of unchanged drug. No dose adjustment of sodium oxybate based on sex is indicated. Although significant food effects were observed, these are minimized in patients by the nocturnal dosing of sodium oxybate hours after the evening meal at a consistent time interval following food ingestion.