This is one of the most recent studies on using ketamine in non-psychotic treatment-resistant depression. The authors were Shiroma et al. from Minneapolis, published Oct 29, 2013.
The study is unique in that the patients maintained their previous antidepressant regimen, with 0.5 mg/kg IV ketamine infusions added on to this regimen, three times per week, for 4 weeks.
11 of 14 patients had a treatment response, and 8 out of 14 had a remission of depressive symptoms.
As one looks at the graphs showing symptom changes over time, it is very apparent that virtually all negative symptoms of depression diminished gradually, with progressive improvements over 3-4 successive infusions. Measures of positive experience (calmness, happiness, and self-esteem) improved in tandem over the same time interval.
As with previous ketamine studies, patients had mild dissociative side effects during the infusion itself, which did not persist beyond a few hours, and which were not subjectively problematic. Hemodynamic changes were minor. One patient had nausea and vomiting.
It is pointed out in the discussion that an active placebo group would be a good idea in a study like this. Giving a saline placebo infusion would be much less informative, because it would be obvious to the patients that they were not receiving ketamine. So the authors discuss the possibility of giving a benzodiazepine active placebo (such as midazolam), etc.
In fact, Murrough et al. have recently conducted a 2-site randomized controlled study of ketamine infusions for treatment-resistant depression patients, using an active placebo group who received IV midazolam ( http://www.ncbi.nlm.nih.gov/pubmed/23982301 ) This study used only one single IV infusion. 47 patients were randomized to receive ketamine, 25 received midazolam. About 60% of the ketamine group had a good symptom response, compared to 30% in the midazolam group, with effects lasting about a week.
So there is continuing evidence of ketamine being a useful antidepressant strategy for treatment-resistant patients. I would like to see more studies using a more convenient dosing regime (e.g. oral or IM dosing) as most psychiatry offices would have a hard time safely administering a 40-minute IV infusion.
I think there is good research data to support short-term trials-- the next big research focus should now be looking at the effectiveness and safety of using intermittent ketamine doses for long periods of time (e.g. every 1-4 weeks, over a period of years, just as we would use maintenance ECT). Most clinicians who are nervous about ketamine as a mainstream treatment would be understandably concerned about long-term health risks. Of course, in my opinion, the long term health risks of continuing treatment-resistant depression symptoms are very severe! -- so even if there was established risk, I think it should be understood and be the patient's choice, just as is the case for so many other potentially dangerous medical treatments (such as immunosuppressants for autoimmune disease, anticonvulsants for epilepsy, antihypertensives for high blood pressure, etc.)
One of the clear long-term risks of ketamine is lower urinary tract damage, including cystitis, with symptoms of urinary urgency, frequency, and dysuria (pain). Here is the best reference I could find that relates the cumulative ketamine dose to a risk of having bladder symptoms:
The authors conclude that risk to the bladder was associated with having 3-5 doses per week of ketamine. Typical doses in this population are at least 12 grams per week, which is at least 300 times more than a weekly dosing regimen used in psychiatry. So the risk with the psychiatric dosing regimen appears to be low, but it is essential to watch very carefully for any evolving urinary tract symptoms.
Ketamine-induced memory dysfunction:
this is a good study warning of long-term cognitive dysfunction due to ketamine use: http://www.ncbi.nlm.nih.gov/pubmed/15500598
Once again, the group they looked at were involved in high-dose frequent recreational drug use, in conjunction with frequent use of alcohol, marijuana, and cocaine. The doses of ketamine involved would probably have also been extremely high and frequent, although oddly the study does not actually even estimate the typical amounts used. The ketamine group showed impairments in various memory functions, with partial improvement over several years of reduced use.
Other authors have shown clear neuropathological changes following 6 months of doses of 1 mg/kg per day. e.g. H. Yu, Q. Li, et al. Chronic ketamine abuse causes dysfunctions of different brain areas relevant to neurodevelopmental psychiatric disorders : Evidence from fMRI in a primate model. This was a poster display (June 7, 2010). This dosing is 14 times higher than the weekly maintenance regimen I would consider reasonable in psychiatry (0.5 mg/kg once per week).
The conclusion here, once again, would be that cognitive impairment is a possibility, but it is probably an issue with very high frequent doses far beyond what would be used in a psychiatric dosing schedule. If ketamine is to be used in a medical setting, it is necessary to regularly assess cognitive functioning.
I am hesitant to consider dosing ketamine more than once per week, given these concerns, unless it was only for an initial 1-2 week course.
Of note, depression itself causes severe cognitive dysfunction in many cases. And other treatments for depression, including sedating antidepressants, antipsychotics, and ECT, have given rise to various cognitive side-effect complaints from patients. I think these are risks to be aware of, to monitor, but then for patient & physician to together make a careful clinical decision regarding risk vs. benefit.