Ketamine has been used to treat neuropathic pain syndromes for over a decade.
Neuropathic pain syndromes include:
CRPS I and II (Complex Regional Pain Syndrome)
RSD (Reflex Sympathetic Dystrophy)
and any chronic pain that involves recruitment of the sympathetic nervous system, which normally does not transmit pain impulses but is in large part responsible for the constant burning pain patients suffer from.
You can use any search engine to find volumes of information on these and other neuropathic pain syndromes. Treatments often include prescription opiates, prescription psychiatric drugs, interventional procedures by a trained pain specialist performed in a sterile procedure room, and behavioral therapy. I encourage all patients to make use of these search engines to educate themselves about their pain as much as possible. It is not my intention to include lengthy explanations here.
In a VERY SIMPLIFIED form, when you have a source of constant pain, your brain effectively begins to assume this is normal. It then recruits the sympathetic nervous system to help transmit pain impulses. This all leads to a great upregulation (your brain makes more of them) of the NMDA receptors in your brain. These are directly involved in the chronic burning pain that accompanies all the other symptoms such as swelling, color change of skin, hyperalgesia, etc. Ketamine works as a great analgesic, but the way it treats this pain is by blocking the NMDA receptors. This blockade causes the brain to now assume these receptors are not needed in such high numbers and down regulation occurs (the brain stops making too many). This is why we believe that the higher the (still sub-anesthetic) dose that can be tolerated, the better the blockade and end result. We feel this is a case where, within reason, more truly is better.
If you suffer from a chronic neuropathic pain syndrome, it is important that you do all you can to identify and treat the root cause because if you are a candidate for ketamine infusion, and it does relieve the neuropathic pain, the continued presence of the root cause can result in a return of the neuropathic component. That said, keep in mind that in some occasions, it is only after the neuropathic pain is relieved that the root cause can then be discovered.
There are numerous protocols for treatment using ketamine, from lower dose given for ten consecutive days (weekends off) to higher doses given for fewer days or even a single day high dose infusion.
Once again I can only relate my personal experience after treating patients for many years (in fact I have been treating pain patients with ketamine longer than all but a very few physicians in the entire USA). I typically tend to use higher doses than most other physicians treating pain with ketamine. In particular if a patient chooses to receive a single infusion I will push the dose to as high a level as I can to try and provide the maximum benefit from the single dose while still maintaining the utmost in safety. If a patient chooses multiple days we will typically start a bit lower and quickly ramp up to the highest dose decided upon. In all treatments, the dose is still sub-anesthetic, partly because it is given over such a long period of time.
It is of extreme importance for all potential ketamine infusion pain patients that they understand and acknowledge that there is no guarantee that the treatment will relieve their pain, even if they are properly diagnosed and treated prior to infusion, and regardless of the number of infusions desired.
That being said, we have experienced cases of clear cut neuropathic pain that did not respond to the first day or two of treatment, but subsequently the pain was relieved by the final three in cases where the patient chose a series of five infusions. While we have had great success with single day high dose treatment, this too may fail to achieve the desired result. It is entirely possible that in at least some of those cases, it was not a case of failure of the treatment, but of too few infusions.
This is another case where trying to predict results is impossible, and deciding on the number of treatments needed is also impossible. I do, however, allow for patients to book a week of infusions, and if the desired result is reached early in the week and the patients prefers not to complete the week, that is their prerogative. The best way to decide is to discuss the treatment with your private pain management doctor, who clearly knows your pain history the best, and between the two of you and your other support givers, decide on a treatment plan.
Each infusion is given over a four hour period, and typical recovery time to discharge is approximately two hours. Many patients, especially those who have had infusions before and are accustomed to the sensations post treatment, leave within an hour, and of course some patients take significantly longer. This is also impossible to predict. After treatment, regardless of the number of infusions, patients are prescribed very low dose oral ketamine for two weeks. This is to continue the NMDA receptor blockade and hopefully increase and prolong the relief.