Vitamin B12 level may be related to the efficacy of single ketamine infusion in bipolar depression.

The single infusion of ketamine, an N-methyl-d-aspartic acid (NMDA) glutamate receptor antagonist, exerts a therapeutic effect in both unipolar and bipolar depression. Homocysteine (HCY) acts agonistically on the NMDA receptor, hyperhomocysteinemia is related to depression, and folic acid and vitamin B12 are associated with HCY system. We estimated the serum levels of these substances in 20 bipolar depressed patients before ketamine infusion. 10 patients responded favorably to this procedure, as their score on the Hamilton depression rating scale, compared to baseline, was reduced by more than 50%, after 7 days. The vitamin B12 level was significantly higher in "responders" compared to the remaining patients. No differences between the 2 groups were found with regard to HCY, folic acid levels and such clinical factors as age, duration of illness and duration of current episode. These preliminary data suggest that the vitamin B12 level may be connected with the efficacy of ketamine infusion in bipolar depression.