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Pain Management

Ketamine and Chronic Pain

Current research on ketamine and pain is focused on the use of this medication for managing treatment-resistant chronic neuropathic pain. Ketamine has shown promise as a treatment for chronic pain that can reduce the use of opioids and provide long-term benefits for patients.

How Does Ketamine Treat Chronic Pain?

Ketamine produces strong analgesia for neuropathic pain patients. It has been shown to inhibit activity at the N-methyl-D-aspartate (NMDA) receptor. The NMDA receptor is responsible for transmission of nociceptive signals. Nociceptors are sensory receptors that detect signals from damaged tissue or the threat of damage. In patients suffering from chronic pain, nociceptors are stimulated in a prolonged way which leads to an increased movement of pain signals to the brain. It is thought that ketamine halts the excessive amplification of pain signals by inhibiting these pain receptors. It is possible ketamine can treat chronic pain by interacting with other receptor systems as well but these interactions are not as well understood yet.

Current research is focused on the use of ketamine for treating chronic neuropathic pain. Pain conditions that have been studied include acute and chronic migraine, fibromyalgia, complex regional pain syndrome, temporomandibular pain (TMJ), phantom limb pain, spinal cord injury, and chronic neuropathic pain of various other causes.

In most studies, ketamine is administered via infusion. It is known that ketamine is effective for reducing neuropathic pain but the key is to find the exact dosage and length of treatment to produce the longest-lasting results. In some cases longer infusion times (e.g. 100 hours) have been used which resulted in prolonged benefits of up to 3 months after treatment. Short infusion times of 30 minutes have resulted in benefits that last less than an hour in duration after treatment.

Ketamine is often combined with benzodiazepines when used to treat chronic pain. Doctors prescribe benzodiazepines to help reduce the psychotropic effects of ketamine.

Ketamine vs. Opioids

For patients who are taking opioid medications to manage their pain, ketamine may be an alternative that helps reduce opioid usage. This reduction in dosage can reduce the incidence of nausea and vomiting. Ketamine is also more effective than opioids at treating neuropathic pain. For patients with certain types of pain, ketamine can work synergistically with opioids to treat multiple components of chronic pain. For other types of pain like that associated with fibromyalgia, opioids may not be effective at all or may even make the condition worse. However ketamine alone has been shown to be an effective treatment for fibromyalgia.

The addictive potential of ketamine is far less than an opioid medication. Although ketamine does have psychotropic effects and is used recreationally, it does not work in the same way as an opioid medication when it comes to addiction potential. The main reasons to try ketamine instead of an opioid involve reducing opioid induced side effects, treating aspects of chronic pain that are not treated as well with opioids, reducing the chances of developing tolerance, and lowering the risk of addiction.

Multimodal Treatment Approach

The best treatment for chronic pain is multimodal. Chronic pain is a multidimensional problem that involves complex processes throughout the body. This means that just one medication alone like ketamine is usually not as effective as medication used in combination or combined with other therapies. Pain has multiple physical, psychological, and behavioral aspects. Therefore treatment often involves physical therapy, lifestyle changes, counseling/psychotherapy, and complementary medicine practices like acupuncture.  This is all in addition to medications like ketamine, opioids, tricyclic antidepressants, etc.

When pain has multiple components, multiple medications are sometimes used to treat each component. For example if a patient experiences pain that has both a neuropathic and inflammatory component, different medications may be used to treat both aspects. Ketamine is FDA approved as a nasal spray for managing depression. This indicates that it may be able to treat multiple aspects of chronic pain including its psychological effects.

Future Research

Future research on ketamine may include studies on whether ketamine can prevent the incidence of chronic pain as well as treat it. This may be useful for certain surgical procedures where chronic pain develops after recovery. Another treatment being studied for chronic pain, which has shown benefits for patients with fibromyalgia, is low dose naltrexone. How does low dose naltrexone interact with ketamine in chronic pain states? Further research is required to better understand these treatments. Especially as opioid use continues to be a widespread problem throughout the U.S., research into less addictive treatments is essential.

Articles

Ketamine for chronic pain: risks and benefits – British Journal of Clinical Pharmacology

Ketamine and Ketamine Metabolite Pharmacology: Insights into Therapeutic Mechanisms – Pharmacological Reviews

Systematic Review of the Use of Intravenous Ketamine for Fibromyalgia – The Ochsner Journal

Multimodal Treatment of Chronic Pain – Medical Clinics of North America

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