The effect of route of administration on the enantioselective pharmacokinetics of ketamine and norketamine in rats.

BACKGROUND: Ketamine has been shown to produce a rapid and potent antidepressant response in patients with treatment-resistant depression. Currently ketamine is most commonly administered as a 40-minute intravenous infusion, though it is unknown whether this is the optimal route of administration.

AIMS: To determine the plasma concentration time course of the R- and S-enantiomers of ketamine and norketamine following administration of ketamine by four different routes of administration.

METHODS: Plasma from conscious non-anaesthetised rats was collected following administration of ketamine by either subcutaneous (SC), intramuscular (IM), intravenous infusion (IVI) or intravenous bolus (IVB) routes of administration. Concentrations of the enantiomers of ketamine and norketamine were determined by LC/MS.

RESULTS: Administration by the SC, IM and IVI routes produced an overall similar drug exposure. In contrast, administration by the IVB route produced approximately 15-fold higher peak plasma concentrations for the enantiomers of ketamine and an approximately four-fold lower AUC for the enantiomers of norketamine.

CONCLUSIONS: Route of administration can significantly influence ketamine and norketamine exposures. These differences may influence safety and tolerability, and potentially drug efficacy in humans. This knowledge adds to current research into the optimisation of the use of ketamine for the treatment of depression.