Perhaps One Day. Ketamine, an anesthetic agent, has recently made headline news. Apparently there is evidence that it acts as an anti-depressant. Some studies have shown in severe treatment resistant patients that ketamine provides significant symptom relief after a single dose within two hours. It's effects can last up to one week. There are potentially dangerous side effects and further research is needed.
Ketamine ; MDD. Some studies show that IV ketamine given in highly specialized clinics can offer rapid relief in severe, treatment-resistant depression: http://tinyurl.Com/l76qma8 however, problems remain in that the beneficial results may not last more than a few days. Also, it's an off-label use -- and there are risks of hallucinations ; dissociation. It's not ready for large-scale use, but some clinics exist.
Unlikely. I don't know for sure. But not to my knowledge. It is a dissociative analgesic unrelated to any other pain medicines. Usually it is not given alone because it does not give a pleasant feeling to the recipient. It is also an intravenous drug and very short acting.
Still under study. This is an area of on-going research. Any use at this time would be "off label". Regarding whether or not psychiatrists will ever prescribe it for bipolar depression, may depend on what the research shows regarding risks and benefits. I think it is too early to say.