More and more patients are being diagnosed with some form of chronic pain. Traditional treatment of chronic pain is based on a trial-and-error approach with antidepressants, anticonvulsants and opioids as drugs of first choice. Irrespective of treatment, just 30-40% of patients experience adequate to good pain relief. The remaining population either displays no effect or responds poorly. Physicians started using the anesthetic ketamine, in low doses, to treat therapy-resistant chronic pain syndrome, especially those syndromes where there is nerve or nerve tissue damage. The recent increase in use of low-dose ketamine in chronic pain is due to the positive effects observed during these treatments.
Ketamine was approved for use by the United States Food and Drug Administration (FDA) in 1970. It is primarily used by veterinarians as a horse tranquilizer. It is a derivative of phencyclidine hydrochloride, which is better known as PCP or angel dust and is one-tenth as potent as PC. It’s original use in humans has been as a general anesthetic to prevent pain and discomfort during medical tests or procedures, or minor surgery. Today its use as an anesthetic agent is diminishing and it’s use in management of pain is growing. Ketamine can be given by various routes and vehicles. It can be injected into veins (intravenous), just beneath the skin (subcutaneous), or directly into muscle (intramuscular). It can also be given orally and topically. Vehicles for administration include creams, gels, liquids, and lozenges.
As newer cleaner drugs or biologics replace ketamine in the operating room, ketamine is finding a new place in clinical therapy as an option for pain management among patients with opioid tolerance, acute hyperalgesia, and chronic neuropathic pain. Ketamine infusions may help some patients with complex regional pain syndrome (a chronic pain condition most often affecting one of the limbs). Many patients have shown significant improvement in their symptoms. Ketamine is not as addictive as opioid, or narcotic, pain relievers. Studies have shown that a single intravenous dose of the medication prior to skin incision was found to decrease postoperative pain and reduce morphine consumption. In controlled trials trauma patients who were given ketamine in addition to morphine prior to arriving at the emergency department had nearly 50 percent better pain management than patients who were given only morphine. Many of the most encouraging clinical trials exploring the use of ketamine in the treatment of chronic pain have been related to neuropathic (nerve) pain. In clinical practice, ketamine is considered safe, and in general, side effects are well tolerated. Drowsiness and dizziness were the most common side effects.
Although ketamine is still used in special circumstances as an anesthetic its usefulness is limited by the fact that at high doses it produces hallucinations and bizarre feelings of dissociation. Patients taking ketamine for prolonged periods are at high-risk for abuse. It has become a recreational drug and abusers inject, inhale, or smoke ketamine. It is referred to as special K or super K on the street. Heavy, prolonged ketamine use can cause cognitive and psychological impairment. When used for chronic pain, ketamine has also been reported to cause dizziness, lightheadedness and nausea. Repeated use has been associated with cases of liver damage and may impair one’s memory.