Drug could be depression buster.

Preliminary evidence indicates that a single dose of a drug called ketamine rapidly quells symptoms of major depression for up to 1 week in patients who don't benefit from standard antidepressant medications. Ketamine lowers brain concentrations of glutamate, a chemical messenger that has been implicated in depression.

A team led by psychiatrist Carlos A. Zarate Jr. of the National Institute of Mental Health in Bethesda, Md., studied 17 adults, ages 19 to 60, whose feelings of helplessness, hopelessness, and other symptoms of major depression had not responded to at least two standard antidepressants.

Participants received in random order two intravenous infusions, a week apart, of ketamine or a saline solution.

The day after an infusion, ketamine produced marked mood improvements in 12 volunteers, compared with reactions to the saline placebo, the researchers report in the August Archives of General Psychiatry. Of the 12, 5 no longer qualified as depressed. Participants typically began to feel better within 2 hours of a ketamine infusion. Ketamine's beneficial effects lasted for at least a week in 6 individuals.

Further research needs to confirm that the response to ketamine exceeds responses produced by drugs, such as intravenous amphetamine, which briefly alter mental state but aren't depression treatments, the researchers say.