Comparison of racemic ketamine and S-ketamine in treatment-resistant major depression: report of two cases.

Recent studies with intravenous infusion of the NMDA receptor antagonist ketamine showed robust and rapid antidepressant effects within hours after treatment. Ketamine is a racemic mixture consisting of two enantiomers, R- and S-ketamine. In contrast to ketamine, S-ketamine is reported to be less prone to psychomimetic side effects, such as derealisation and hallucinations. In this report we describe the effect of ketamine and S-ketamine infusion therapy, respectively, in two patients with treatment-resistant major depression. Severity of depression was rated using the Hamilton Depression Rating Scale (HAMD) and the Beck Depression Inventory (BDI). While one patient did not respond to either treatment, in the other patient intravenous administration of ketamine as well as S-ketamine showed an antidepressant effect as assessed by a decrease in HAMD-21 and BDI at days 1 and 3 after infusion which faded until day 6. Both patients experienced psychomimetic side effects during ketamine infusion which were absent during treatment with S-ketamine. We conclude that S-ketamine might exert similar antidepressant effects as ketamine in drug-resistant depression but may be better tolerated by the patients.