New research suggests that just one dose of the anesthetic ketamine appears to reduce depression in patients who show little improvement with standard medications.
Researchers say the beneficial effects start less than 2 hours after the drug is given and last for about 7 days.
According to a study by researchers at the National Institutes of Health in Bethesda, Maryland, most existing treatments for depression can take weeks or months to relieve people's symptoms and any treatment which provides an antidepressant effect during this lag time would be of major benefit.
Dr. Carlos A. Zarate, Jr, and his team looked at ketamine as a possible treatment because it blocks an enzyme system that seems to play a key role in depression.
For the research the team studied a group which included 17 patients with severe depression who had not responded to at least two trials of antidepressants.
The participants were required to have a score of at least 18 on a standard depression test called the Hamilton Depression Rating Scale (HDRS).
In the trial, the patients were given an intravenous infusion of ketamine or an inactive "placebo," then switched to an infusion of the other agent one week later.
In order to assess the onset and duration of effect, Zarate and his team used the HDRS an hour before the infusion, and at 40, 80, 110, and 230 minutes afterwards, then on days 1, 2, 3, and 7 days.
They found the patients treated with ketamine scored significantly lower on the HDRS at 110 minutes, lasting through 7 days, compared with those receiving placebo treatment and the time that the antidepressant response began and lasted was "nearly identical" for each subject.
The prolonged antidepressant effect that occurred with ketamine they say is remarkable considering its short half-life, which is approximately 2 hours.
Apparently none of the patients had any response to the placebo.
The team suggest that ketamine is faster acting because it is targeting a different brain-protein, called the NMDA receptor, which is thought to play a critical role in learning and memory.
But they do say however that ketamine in its current form, would not be appropriate for medication and would need to be altered so it lost its existing hallucinatory side-effects.
The study is published in the Archives of General Psychiatry, August 2006.