Population pharmacokinetics of S-ketamine and norketamine in healthy volunteers after intravenous and oral dosing.

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Fanta S, Kinnunen M, Backman JT, Kalso E

Population pharmacokinetics of S-ketamine and norketamine in healthy volunteers after intravenous and oral dosing.

Eur J Clin Pharmacol. 2015 Apr;71(4):441-7. doi: 10.1007/s00228-015-1826-y. Epub 2015 Mar 1.

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25724645 [ View in PubMed
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Abstract

PURPOSE: Low-dose ketamine is a lucrative therapeutic approach in cancer pain, perioperative treatment of pain, and management of treatment-resistant depression. The analgesic potency of its main metabolite norketamine is thought to be one third that of ketamine. However, few studies exist on the pharmacokinetics of orally administered S-ketamine. METHODS: In our study, 11 healthy volunteers received S-ketamine 0.25 mg/kg orally and 0.125 mg/kg intravenously. S-ketamine and norketamine concentrations were measured up to 23.5 h post-dose. A population pharmacokinetic model was built to describe S-ketamine and norketamine pharmacokinetics. RESULTS: A three-compartment model for both S-ketamine and norketamine best described the data. To accommodate for the extensive formation of norketamine after oral S-ketamine, a separate presystemic absorption-phase component was included in addition to its systemic formation. The oral bioavailability of S-ketamine was low, 8% (11% interindividual variability), and its clearance was high, 95 L/h/70 kg (13% interindividual variability). Simulations suggested that after oral dosing, norketamine AUC at steady state is 16.5 times higher than that of S-ketamine. CONCLUSIONS: Given that the analgesic effect of S-ketamine is due to both S-ketamine and norketamine, relatively small oral doses of S-ketamine can be assumed to be a feasible alternative to repeated intravenous dosing, for example in the setting of chronic pain.

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