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Ketamine is a drug used in human and veterinary medicine. Its hydrochloride salt is sold as Ketanest, Ketaset, and Ketalar. Pharmacologically, Ketamine is classified as an NMDA receptor antagonist. At high, fully anesthetic level doses, ketamine has also been found to bind to opioid μ receptors type 2 in cultured human neuroblastoma cells, however without agonist activity, and to sigma receptors in rats. Also, ketamine interacts with muscarinic receptors, descending monoaminergic pain pathways and voltage-gated calcium channels. Like other drugs of this class such as tiletamine and phencyclidine (PCP), it induces a state referred to as "dissociative anesthesia" and is used as a recreational drug.

Ketamine has a wide range of effects in humans, including analgesia, anesthesia, hallucinations, elevated blood pressure, and bronchodilation. Ketamine is primarily used for the induction and maintenance of general anesthesia, usually in combination with a sedative. Other uses include sedation in intensive care, analgesia (particularly in emergency medicine), and treatment of bronchospasm. It has been shown to be effective in treating depression in patients with bipolar disorder who have not responded to other anti-depressants. In persons with major depressive disorder it produces a rapid antidepressant effect, acting within two hours as opposed to the several weeks taken by typical antidepressants to work. It is also a popular anesthetic in veterinary medicine.

Ketamine is a chiral compound. Most pharmaceutical preparations of ketamine are racemic; however, some brands reportedly have (mostly undocumented) differences in enantiomeric proportions. The more active enantiomer, (S)-ketamine, is also available for medical use under the brand name Ketanest S.[10] (R)-ketamine, (S)-ketamine & racemic (R,S)-ketamine all have qualitatively separate distinct effect profiles, although S has the most active potency. Ketamine is a core medicine in the World Health Organization's "Essential Drugs List", a list of minimum medical needs for a basic health care system.

Medical use

Indications for use as an anaesthetic:

* Pediatric anesthesia (as the sole anesthetic for minor procedures or as an induction agent followed by muscle relaxant and endotracheal intubation)
* Asthmatics or patients with chronic obstructive airway disease
* As part of a cream, gel, or liquid for topical application for nerve pain—the most common mixture is 10% ketoprofen, 5% Lidocaine, and 10% ketamine. Other ingredients found useful by pain specialists and their patients as well as the compounding pharmacists who make the topical mixtures include amitriptyline, cyclobenzaprine, clonidine, tramadol, and mepivicaine and other longer-acting local anaesthetics.
* In emergency medicine in entrapped patients suffering severe trauma
* Emergency surgery in field conditions in war zones
* To supplement spinal / epidural anesthesia / analgesia utilizing low doses

In medical settings, ketamine is usually injected intravenously or intramuscularly. Since it suppresses breathing much less than most other available anaesthetics, ketamine is still used in human medicine as an anesthetic, however, due to the hallucinations which may be caused by ketamine, it is not typically used as a primary anesthetic, although it is the anaesthetic of choice when reliable ventilation equipment is not available. Ketamine tends to increase heart rate and blood pressure. Because ketamine tends to increase or maintain cardiac output, it is sometimes used in anesthesia for emergency surgery when the patient's fluid volume status is unknown (e.g., from traffic accidents). Ketamine can be used in podiatry and other minor surgery, and occasionally for the treatment of migraine. There is ongoing research in France, the Netherlands, Russia, Australia and the US into the drug's usefulness in pain therapy, depression suppression, and for the treatment of alcoholism and Heroin addiction.

In veterinary anesthesia, ketamine is often used for its anesthetic and analgesic effects on cats, dogs, rabbits, rats, and other small animals. Veterinarians often use ketamine with sedative drugs to produce balanced anesthesia and analgesia, and as a constant rate infusion to help prevent pain wind-up. Ketamine is used to manage pain among large animals, though it has less effect on bovines. It is the primary intravenous anesthetic agent used in equine surgery, often in conjunction with detomidine and thiopental, or sometimes guaifenesin.

Ketamine may be used in small doses (0.1–0.5 mg/kg·h) as a local anesthetic, particularly for the treatment of pain associated with movement and neuropathic pain.[17] It may also be used as an intravenous co-analgesic together with opiates to manage otherwise intractable pain, particularly if this pain is neuropathic (pain due to vascular insufficiency or shingles are good examples). It has the added benefit of counter-acting spinal sensitization or wind-up phenomena experienced with chronic pain. At these doses, the psychotropic side effects are less apparent and well managed with benzodiazepines. Ketamine is a co-analgesic, and so is most effective when used alongside a low-dose opioid; while it does have analgesic effects by itself, the higher doses required can cause disorienting side effects. The combination of ketamine with an opioid is, however, particularly useful for pain caused by cancer.

The effect of ketamine on the respiratory and circulatory systems is different from that of other anesthetics. When used at anesthetic doses, it will usually stimulate rather than depress the circulatory system. It is sometimes possible to perform ketamine anesthesia without protective measures to the airways. Ketamine is also a potent analgesic and can be used in sub-anesthetic doses to relieve acute pain; however, its psychotropic properties must be taken into account. Patients have reported vivid hallucinations, "going into other worlds" or "seeing God" while anesthetized, and these unwanted psychological side-effects have reduced the use of ketamine in human medicine. They can, however, usually be avoided by concomitant application of a sedative such as a benzodiazepine.

Low-dose ketamine is recognized for its potential effectiveness in the treatment of complex regional pain syndrome (CRPS), according to a retrospective review published in the October 2004 issue of Pain Medicine. Although low-dose ketamine therapy is established as a generally safe procedure, reported side effects in some patients have included hallucinations, dizziness, lightheadedness and nausea. Therefore nurses administering ketamine to patients with CRPS should only do so in a setting where a trained physician is available if needed to assess potential adverse effects on patients.

In some neurological ICUs, ketamine has been used in cases of prolonged status epilepticus. There has been some evidence that the NMDA-blocking effect of the drug protects neurons from glutamatergic damage during prolonged seizures.

Experimental antidepressant use

When treating patients suffering from complex regional pain syndrome (CRPS) with a low-dose (subanesthetic) ketamine infusion, it was observed that some patients made a significant recovery from associated depression. This recovery was not formally documented, as the primary concern was pain management. It was not possible to quantify to what degree depression recovery was secondary to the patient's recovery from CRPS.

One trial administered a short-term ketamine regimen to patients with severe depression, with the dose carefully monitored to prevent hallucinogenic side effects. The patients' normal medications were continued as it was feared that stopping them might result in severe depressive episodes. Before and following each treatment with ketamine, at patient clinic visits, the Beck Depression Inventory (BDI) and the Hamilton Rating Scale for Depression (HAMD-17) were obtained. Two of the patients demonstrated significant, long-term improvement. Another small study found that ketamine significantly improved treatment-resistant major depression within hours of injection. The improvement lasted up to one week after the single dose. These patients were previously treatment resistant, having tried an average of six other treatments that failed. NIMH director Dr. Thomas Insel remarked:

"To my knowledge, this is the first report of any medication or other treatment that results in such a pronounced, rapid, prolonged response with a single dose. These were very treatment-resistant patients."

The researchers apparently attribute the effect to ketamine being an NMDA receptor antagonist. Those findings of Zarate et al. corroborate earlier findings by Berman et al.. However Zarate et al. do raise some concerns about their results due to a possible lack of blinding, because of the inebriating effects of low dose ketamine infusion, and it is recommended that future studies include an active placebo.

These findings are corroborated by Liebrenz et al., who successfully, according to an attending doctor, treated a patient with a treatment-resistant major depression and a co-occurring alcohol and benzodiazepine dependence by giving an intravenous infusion of 0.5 mg/kg ketamine over a period of 50 minutes and Goforth et al. who helped a patient with severe, recurrent major depressive disorder that demonstrated marked improvement within 8 hours of receiving a preoperative dose of ketamine and one treatment of electroconvulsive therapy with bitemporal electrode placement.

However, a new study in mice by Zarate et al. shows that blocking the NMDA receptor is an intermediate step. According to this study, blocking NMDA increases the activity of another receptor, AMPA, and this boost in AMPA activity is crucial for ketamine’s rapid antidepressant actions. NMDA and AMPA are receptors for the neurotransmitter glutamate. The glutamate system has been implicated in depression recently. This is a departure from previous thinking, which had focused on serotonin and norepinephrine. The glutamate system may represent a new avenue for treatment and research.

Krystal et al. retrospectively compared the seizure duration, ictal EEG, and cognitive side effects of ketamine and methohexital anesthesia with ECT in 36 patients. Ketamine was well tolerated and prolonged seizure duration overall, but particularly in those who had a seizure duration shorter than 25 seconds with methohexital at the maximum available stimulus intensity. Ketamine also increased midictal EEG slow-wave amplitude. Thus, a switch to ketamine may be useful when it is difficult to elicit a robust seizure. Faster post-treatment reorientation with ketamine may suggest a lower level of associated cognitive side effects.

Kudoh et al. investigated whether ketamine is suitable for depressed patients who had undergone orthopedic surgery. Depressed mood, suicidal tendencies, somatic anxiety, and hypochondriasis significantly decreased in the active group as compared with the control. The group receiving ketamine also had significantly lower postoperative pain.

Acute administration of ketamine at the higher dose, but not imipramine, increased BDNF protein levels in the rat hippocampus. The increase of hippocampal BDNF protein levels induced by ketamine might be necessary to produce a rapid onset of antidepressant action in rats.

Treatment of addiction

The Russian doctor Evgeny Krupitsky (Clinical Director of Research for the Saint Petersburg Regional Center for Research in Addiction and Psychopharmacology) has claimed to have encouraging results by using ketamine as part of a treatment for alcohol addiction which combines psychedelic and aversive techniques. This method involved psychotherapy, controlled ketamine use and group therapy, and resulted in 60 of the 86 alcoholic males selected for the study remaining fully abstinent through one year of treatment. For heroin addiction, the same researcher reached the conclusion that one ketamine-assisted psychotherapy session was significantly more effective than active placebo in promoting abstinence from heroin during one year without any adverse reactions. In a recently published study 59 detoxified inpatients with heroin dependence received a ketamine-assisted psychotherapy (KPT) session prior to their discharge from an addiction treatment hospital, and were then randomized into two treatment groups.

Participants in the first group received two addiction counseling sessions followed by two KPT sessions, (with a single im injection of 2 mg/kg ketamine) with sessions scheduled on a monthly interval (multiple KPT group). Participants in the second group received two addiction counseling sessions on a monthly interval, but no additional ketamine therapy sessions (single KPT group). At one-year follow-up, survival analysis demonstrated a significantly higher rate of abstinence in the multiple KPT group. Thirteen out of 26 subjects (50%) in the multiple KPT group remained abstinent, compared to 6 out of 27 subjects (22.2%) in the single KPT group (p < 0.05). No differences between groups were found in depression, anxiety, craving for heroin, or their understanding of the meaning of their lives. It was concluded that three sessions of ketamine-assisted psychotherapy are more effective than a single session for the treatment of heroin addiction.

Krupitsky and Kolp summarized their work to date in 2007.

Jovaisa et al. from Lithuania demonstrated attenuation of opiate withdrawal symptoms with ketamine. A total of 58 opiate-dependent patients were enrolled in a randomized, placebo-controlled, double-blind study. Patients underwent rapid opiate antagonist induction under general anesthesia. Prior to opiate antagonist induction patients were given either placebo (normal saline) or subanesthetic ketamine infusion of 0.5 mg/kg·h. Ketamine group presented better control of withdrawal symptoms, which lasted beyond ketamine infusion itself. Significant differences between ketamine and Control groups were noted in anesthetic and early postanesthetic phases. There were no differences in effects on outcome after 4 months.

Complex regional pain syndrome

Ketamine is being used as an experimental and controversial treatment for Complex Regional Pain Syndrome (CRPS) also known as Reflex Sympathetic Dystrophy (RSD). CRPS/RSD is a severe chronic pain condition characterized by sensory, autonomic, motor and dystrophic signs and symptoms. The pain in CRPS is continuous, it worsens over time, and it is usually disproportionate to the severity and duration of the inciting event. The hypothesis is that ketamine manipulates NMDA receptors which might reboot aberrant brain activity. There are two treatment modalities, the first consist of a low dose ketamine infusion of between 25–90 mg per day, over five days either in hospital or as an outpatient. This is called the awake technique. Open label, prospective, pain journal evaluation of a 10-day infusion of intravenous ketamine (awake technique) in the CRPS patient concluded that "A four-hour ketamine infusion escalated from 40–80 mg over a 10-day period can result in a significant reduction of pain with increased mobility and a tendency to decreased autonomic dysregulation".

Case notes of 33 patients whose CRPS pain was treated by the inpatient administration of a continuous subanesthetic intravenous infusion of ketamine were reviewed at Mackay Base Hospital, Queensland, Australia. A total of 33 patients with diagnoses of CRPS who had undergone ketamine treatment at least once were identified. Due to relapse, 12 of 33 patients received a second course of therapy, and two of 33 patients received a third. There was complete pain relief in 25 (76%), partial relief in six (18%), and no relief in two (6%) patients.

The degree of relief obtained following repeat therapy (N=12) appeared even better, as all 12 patients who received second courses of treatment experienced complete relief of their CRPS pain. The duration of relief was also impressive, as was the difference between the duration of relief obtained after the first and after the second courses of therapy. In this respect, following the first course of therapy, 54% of 33 individuals remained pain free for 3 months or more and 31% remained pain free for 6 months or more. After the second infusion, 58% of 12 patients experienced relief for a year or more, while almost 33% remained pain free for over 3 years. The most frequent side effect observed in patients receiving this treatment was a feeling of inebriation. Hallucinations occurred in six patients. Less frequent side effects also included complaints of light-headedness, dizziness, and nausea. In four patients, an alteration in hepatic enzyme profile was noted; the infusion was terminated and the abnormality resolved thereafter. No long-term side-effects were noted.

The second treatment modality consists of putting the patient into a medically-induced coma and given an extremely high dosage of ketamine; typically between 600–900 mg. This version, currently not allowed in the United States, is most commonly done in Germany but some treatments are now also taking place in Monterrey, Mexico. According to Dr Schwartzman, 14 cases out of 41 patients in the coma induced ketamine experiments were completely cured. "We haven't cured the original injury", he says, "but we have cured the RSD or kept it in remission. The RSD pain is gone." He added that "No one ever cured it before... In 40 years, I have never seen anything like it. These are people who were disabled and in horrible pain. Most were completely incapacitated. They go back to work, back to school, and are doing everything they used to do. Most are on no medications at all. I have taken morphine pumps out of people. You turn off the pain and reset the whole system."

In Tuebingen, Germany Dr Kiefer treated a patient presented with a rapidly progressing contiguous spread of CRPS from a severe ligamentous wrist injury. Standard pharmacological and interventional therapy successively failed to halt the spread of CRPS from the wrist to the entire right arm. Her pain was unmanageable with all standard therapy. As a last treatment option, the patient was transferred to the intensive care unit and treated on a compassionate care Basis with anesthetic doses of ketamine in gradually increasing (3–5 mg/kg·h) doses in conjunction with midazolam over a period of 5 days. On the second day, edema, and discoloration began to resolve and increased spontaneous movement was noted. On day 6, symptoms completely resolved and infusions were tapered. The patient emerged from anesthesia completely free of pain and associated CRPS signs and symptoms. The patient has maintained this complete remission from CRPS for 8 years now. The psychiatric side effects of ketamine were successfully managed with the concomitant use of midazolam and resolved within 1 month of treatment.

Postoperative pain

The dissociative anesthetic effects of ketamine have also been applied within the realm of postoperative pain management. Low doses of ketamine have been found to significantly reduce morphine consumption as well as reports of nausea following abdominal surgery[/lang] [2]

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