New Research on Ketamine
The drug ketamine can produce antidepressant effects within hours when administered intravenously.
Finding an Appropriate Control
Comparing ketamine to placebo has challenges because ketamine produces mild dissociative effects (such as a feeling of distance from reality) that are noticeable to patients. At the 2013 meeting of the Society of Biological Psychiatry, James W. Murrough and collaborators at the Mount Sinai School of Medicine reported their findings from the first controlled trial of intravenous ketamine in depression that uses an active control, the short-acting benzodiazepine midazolam, which has sedative effects and decreases anxiety, but is not known as an antidepressant. On virtually all measures intravenous ketamine was a more effective antidepressant following 2 infusions per week.
These data help dispel one of the criticisms of intravenous ketamine, that studies of the drug have not been sufficiently blinded (when patients and medical staff are kept from knowing which patients receive an active treatment and which are in the placebo control group) and that the lack of an appropriate active placebo contributed to the dramatic findings about ketamine’s antidepressant effects. It now appears that these criticisms have been appropriately answered and that intravenous ketamine is highly effective not only in comparison to placebo but also to an active comparator.
This research was presented as a poster at the meeting and published as abstract #442 in the meeting supplement to the journal Biological Psychiatry, Volume 73, Number 9S, and was also published in the Archives of General Psychiatry in 2013.
Slowing Down Ketamine Infusions to Reduce Side Effects
Ketamine is commonly given in 40-minute intravenous infusions. Timothy Lineberry from the Mayo Clinic reported in Abstract #313 from the meeting that slower infusions of ketamine over 100 minutes were also effective in producing antidepressant effects in patients with treatment-resistant depression. Lineberry’s research group used the slower infusion in order to increase safety and decrease side effects, such as the dissociative effects discussed above. In the 10 patients the group studied, they observed a response rate of 80% and a remission rate of 50% (similar to ketamine’s effects with 40-minute infusions).
Family or Personal History of Alcohol Dependence Predicts Positive Response to Ketamine in Depression
Mark J. Niciu and collaborators at the NIMH reported in Abstract #326 that a personal or family history of alcohol dependence predicted a positive response to IV ketamine in patients with unipolar depression.
Ketamine Acts on Monoamines in Addition to Glutamate
Ketamine’s primary action in the nervous system is to block glutamate NMDA receptors in the brain. In addition to its effects on glutamate, it may also affect the monoamines norepinephrine and dopamine. Kareem S. El Iskandarani et al. reported in Abstract #333 that in a study of rats, ketamine increased the firing rate of norepinephrine neurons in a part of the brain called the locus coeruleus and also increased the number of spontaneous firing dopamine cells in the ventral tegmental area of the brain.
Editor’s Note: These data showing that ketamine increased the activity of two monoamines could help explain ketamine’s ability to induce rapid onset of antidepressant effects, in addition to its ability to immediately increase brain-derived neurotrophic factor (BDNF, important for long-term memory and the creation of new synapses) and to restore healthy mushroom-shaped spines on the dendrites of neurons in the prefrontal cortex.
