S-ketamine concentrations are greatly increased by grapefruit juice.

purposeWe examined the effect of grapefruit juice on the pharmacokinetics and pharmacodynamics of oral S-ketamine.

methodsA randomized crossover open-label study design with two phases at an interval of 4 weeks was conducted in 12 healthy volunteers. Grapefruit juice or water was ingested 200 ml t.i.d. for 5 days. An oral dose of 0.2 mg/kg of S-ketamine was ingested on day 5 with 150 ml grapefruit juice or water. Plasma concentrations of ketamine and norketamine were determined for 24 h, and pharmacodynamic variables were recorded for 12 h. Noncompartmental methods were used to calculate pharmacokinetic parameters.

resultsGrapefruit juice increased the geometric mean value of the area under the plasma ketamine concentration-time curve(AUC0-∞) by 3.0-fold (range 2.4- to 3.6-fold; P<0.001), the peak plasma concentration (Cmax) by 2.1-fold (range 1.8- to 2.6-fold; P<0.001), and the elimination half-life by 24% (P<0.05) as compared to the water phase. The ratio of main metabolite norketamine to ketamine (AUCm/AUCp) was decreased by 57% (P<0.001) during the grapefruit phase.Self-rated relaxation was decreased (P<0.05) and the performance in the digit symbol substitution test was increased (P<0.05) after grapefruit juice, but other behavioral or analgesic effects were not affected.

conclusionsGrapefruit juice significantly increased the plasma concentrations of oral ketamine in healthy volunteers.Dose reductions of ketamine should be considered when using oral ketamine concomitantly with grapefruit juice.