Glia a Promising Target for Neuropathic Pain – Ketamine Acting on Glia More Than on Neuronal NMDA Receptors?

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 Three important new articles from March, August and November 2011, show ketamine acts on glia.

Emphasis within articles is mine.

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Microglia: a promising target for treating neuropathic and postoperative pain, and morphine tolerance.

Abstract

Management of chronic pain, such as nerve-injury-induced neuropathic pain associated with diabetic neuropathy, viral infection, and cancer, is a real clinical challenge. Major surgeries, such as breast and thoracic surgery, leg amputation, and coronary artery bypass surgery, also lead to chronic pain in 10-50% of individuals after acute postoperative pain, partly due to surgery-induced nerve injury. Current treatments mainly focus on blocking neurotransmission in the pain pathway and have only resulted in limited success. Ironically, chronic opioid exposure might lead to paradoxical pain. Development of effective therapeutic strategies requires a better understanding of cellular mechanisms underlying the pathogenesis of neuropathic pain. Progress in pain research points to an important role of microglial cells in the development of chronic pain. Spinal cord microglia are strongly activated after nerve injury, surgical incision, and chronic opioid exposure. Increasing evidence suggests that, under all these conditions, the activated microglia not only exhibit increased expression of microglial markers CD 11 b and Iba 1, but also display elevated phosphorylation of p38 mitogen-activated protein kinase. Inhibition of spinal cord p38 has been shown to attenuate neuropathic and postoperative pain, as well as morphine-induced antinociceptive tolerance. Activation of p38 in spinal microglia results in increased synthesis and release of the neurotrophin brain-derived neurotrophic factor and the proinflammatory cytokines interleukin-1β, interleukin-6, and tumor necrosis factor-α. These microglia-released mediators can powerfully modulate spinal cord synaptic transmission, leading to increased excitability of dorsal horn neurons, that is, central sensitization, partly via suppressing inhibitory synaptic transmission. Here, we review studies that support the pronociceptive role of microglia in conditions of neuropathic and postoperative pain and opioid tolerance. We conclude that targeting microglial signaling might lead to more effective treatments for devastating chronic pain after diabetic neuropathy, viral infection, cancer, and major surgeries, partly via improving the analgesic efficacy of opioids.

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Ketamine depresses toll-like receptor 3 signaling in spinal microglia in a rat model of neuropathic pain.

Abstract

Reports suggest that microglia play a key role in spinal nerve ligation (SNL)-induced neuropathic pain, and toll-like receptor 3 (TLR3) has a substantial role in the activation of spinal microglia and the development of tactile allodynia after nerve injury. In addition, ketamine application could suppress microglial activation in vitro, and ketamine could inhibit proinflammatory gene expression possibly by suppressing TLR-mediated signal transduction. Therefore, the present study was designed to disclose whether intrathecal ketamine could suppress SNL-induced spinal microglial activation and exert some antiallodynic effects on neuropathic pain by suppressing TLR3 activation. Behavioral results showed that intrathecal ketamine attenuated SNL-induced mechanical allodynia, as well as spinal microglial activation, in a dose-dependent manner. Furthermore, Western blot analysis displayed that ketamine application downregulated SNL-induced phosphorylated-p38 (p-p38) expression, which was specifically expressed in spinal microglia but not in astrocytes or neurons. Besides, ketamine could reverse TLR3 agonist (polyinosine-polycytidylic acid)-induced mechanical allodynia and spinal microglia activation. It was concluded that intrathecal ketamine depresses TLR3-induced spinal microglial p-p38 mitogen-activated protein kinase pathway activation after SNL, probably contributing to the antiallodynic effect of ketamine on SNL-induced neuropathic pain.

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Microglial Ca(2+)-activated K(+) channels are possible molecular targets for the analgesic effects of S-ketamine on neuropathic pain.

Abstract

Ketamine is an important analgesia clinically used for both acute and chronic pain. The acute analgesic effects of ketamine are generally believed to be mediated by the inhibition of NMDA receptors in nociceptive neurons. However, the inhibition of neuronal NMDA receptors cannot fully account for its potent analgesic effects on chronic pain because there is a significant discrepancy between their potencies. The possible effect of ketamine on spinal microglia was first examined because hyperactivation of spinal microglia after nerve injury contributes to neuropathic pain. Optically pure S-ketamine preferentially suppressed the nerve injury-induced development of tactile allodynia and hyperactivation of spinal microglia. S-Ketamine also preferentially inhibited hyperactivation of cultured microglia after treatment with lipopolysaccharide, ATP, or lysophosphatidic acid. We next focused our attention on the Ca(2+)-activated K(+) (K(Ca)) currents in microglia, which are known to induce their hyperactivation and migration. S-Ketamine suppressed both nerve injury-induced large-conductance K(Ca) (BK) currents and 1,3-dihydro-1-[2-hydroxy-5-(trifluoromethyl)phenyl]-5-(trifluoromethyl)-2H-benzimidazol-2-one (NS1619)-induced BK currents in spinal microglia. Furthermore, the intrathecal administration of charybdotoxin, a K(Ca) channel blocker, significantly inhibited the nerve injury-induced tactile allodynia, the expression of P2X(4) receptors, and the synthesis of brain-derived neurotrophic factor in spinal microglia. In contrast, NS1619-induced tactile allodynia was completely inhibited by S-ketamine. These observations strongly suggest that S-ketamine preferentially suppresses the nerve injury-induced hyperactivation and migration of spinal microglia through the blockade of BK channels. Therefore, the preferential inhibition of microglial BK channels in addition to neuronal NMDA receptors may account for the preferential and potent analgesic effects of S-ketamine on neuropathic pain.

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The material on this site is for informational purposes only,

The material on this site is for informational purposes only,

and is not a substitute for medical advice, diagnosis or treatment provided by a qualified health care provider.


For My Home Page, click here: 

Welcome to my Weblog on Pain Management!

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Ketamine

Ketamine for persons with severe pain

cancerIn special circumstances, I may suggest a trial of low dose oral ketamine. It is formulated by a compounding pharmacist as an oral suspension. It is safe to use without significant adverse effects, though you may experience transient symptoms lasting 20 to 40 minutes after the first few doses. For most people, it may relieve pain when all other methods have failed, possibly including total pain relief with no side effects in patients who have then been able to discontinue all opioids.

Keep all your medicine, opioids and ketamine, in a lock box to prevent abuse by others. This is a Schedule III drug like Vicodin.

Achieving control of chronic pain requires a partnership

based upon trust and effort

Requirements: I will work closely with you on ketamine and ask you to keep a log of pain before each dose and 30 minutes after. In addition, for the first week I ask that you log blood pressure and heart rate before each dose and 30 minutes after. This requires that you see me in the office one week later. If you have any questions or problems, I ask that you call me the same day, whether it be weekend or holiday. If you are unable to keep these logs before and after the dose, and the appointment one week later, the trial will be discontinued. You have no authority to continue without my consent.

Blood Pressure: Usually no change occurs in blood pressure. Some have reported that ketamine lowers their blood pressure and they are lightheaded when they stand up. If your blood pressure drops or if you are lightheaded, be very cautious as that may lead to fainting and brief loss of consciousness. Anytime a person faints, that could result in potentially serious injury such as hip fracture, other fractures, bleeding or brain injury if you strike your head. Your blood pressure should be above 100 when standing.  Ketamine has been reported to increase blood pressure and pulse, but I have not found that to occur with these doses.

Side Effects: Ketamine has a very narrow therapeutic window for pain control. This means that once you find the dose that relieves pain, a very slight increase in dose may produce intolerable side effects. Unfortunately some patients reach a dose that produces side effects before they experience any pain relief.

Most patients have no side effects with the low doses used by this protocol, though some may have mild symptoms lasting up to 40 minutes. If you do, then try decreasing the dose a small amount.

It is possible but rare that you may experience severe, frightening hallucinations or may feel you are outside the body observing it do things, called a dissociative reaction.

These side effects are dose related and have been short lasting, usually no longer than 40 minutes.  The antidote is Ativan.

Steps to follow: Read all steps carefully before you begin

  • Take ketamine 30 minutes prior to your other pain medication
  • For the first dose, remain seated or lie down for 20 minutes after you take the dose to avoid risk of falling. Do not take the dose and walk around.
  • A few persons have had severe imbalance lasting 10 or 20 minutes. This has resolved after the first few doses in those persons. It may not happen to you, so test with caution. If it has not occurred at the first dose, it is unlikely to occur at all.
  • Follow the dosing guidelines in the log I give you and which I repeat in this next step:
    Begin with 0.25 mL and increase by increments of 0.25 mL every 6 hours or longer than 6 hours, until you have some pain relief. Do not increase that dose or dosing interval.

Example: begin 0.25 mL, then 0.5, next 0.75, 1.0, 1.25, 1.5, 1.75, 2.0

If you have had no effect on pain by 2.0 mL, schedule an appointment for further instructions.
If your pain decreases only 1 or 2 points, that is your dose.  It will NOT get better by increasing the dose.  Stop increasing.

  • If you have intolerable side effects, you may use 1 or 2 Ativan tablets immediately as an antidote, and every 30 minutes, up to 5 of them.
  • CAUTION: Be alert to the opioid-sparing effects of ketamine!

This means that if ketamine relieves your pain, you do not need to take the opioid as that would be an opioid overdose and may cause serious side effects.

Reduce or temporarily stop your opioid medication if pain is gone after using ketamine.

This is why you take ketamine 30 minutes before the opioid. Some people have been able to completely stop all opioid medication due to pain relief from ketamine alone.

  • CAUTION: Do not drive for 6 hours after a dose.

This is for the protection of you and others. You may not be aware of very subtle side effects.

  • You may take a dose every 6 hours, or longer than 6 hours. Less is more.

If ketamine loses its effect, stop use for 2 or 3 days, then resume. It can be a fickle drug.  That is why increasing the dose causes loss of effect.

Some take ketamine only before sleep. If you do that, use it 30 minutes before sleep in order to log its effect and take blood pressure/pulse before and after. Continue this initially until further changes are approved.

Ketamine was approved for use as an anesthetic by the FDA in 1970

It’s use for pain is “off label” as it was approved only in high doses for anesthesia. It has been used safely in babies. Unlike opioids, it does not depress breathing or bowel function, and usually does not depress cardiovascular function. Since the late 1980′s, numerous scientific articles have been published on its use as a third line choice for some pain conditions; there are few double blind control studies, one is listed below. If you search ketamine on various internet search engines you find it is abused by addicts just as other drugs are. You find medical articles when you search the literature using Google Scholar or PubMed in the National Library of Medicine. If you find a medical article with adverse effects, let me know. I have spoken to leading brain and psychiatric researchers who have verified there are no lasting side effects from its use.

Many publications on ketamine use multi-day infusions at much higher dosages than the oral dosages in my protocol. Drexel University has treated over 3,000 patients with infusions of 40 mg/hour for 5 days with no lasting adverse effects. Even higher doses than that are used for surgical anesthesia. Ketamine is a powerful tool for treating pain.

Medical Publications


You can click and download each reference in blue below

High dose ketamine improves neurological outcome after stroke in rats, Reeker et al, Canadian J Anesth 47:572-578, 2000

Ketamine, Pasero C, McCaffery M, Amer J Nursing, 105:60-64, 2005
An excellent review, more clinical, easier to read than some more technical papers

Ketamine in Chronic Pain Management: An Evidence Based Review, Hocking & Cousins, Anesth Analg, 97(6):1730-1739, 2003This nine page article is the best comprehensive review of ketamine’s use in almost every known pain condition including post stroke pain.  Easier to read; a catalogue of pain syndromes and references.

Ketamine Stops Aura in Familial Hemiplegic Migraine, Neurology, 55:139-141, 2000 Two mechanisms may account for this. First, ketamine can increase cerebral blood flow, which may counteract the marked hypoperfusion induced by cortical spreading depression, as observed in migraine with aura. Second, in experimental animals, ketamine accelerates the  restitution of neuronal function after hypoxia.

Ketamine oral use in 8 chronic pain patients, Canadian J. of Anesthesia, 2004


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The Reflex Sympathetic Dystrophy Association library has many articles on RSD, CRPS and ketamine. Remember most of the articles are written for scientists and physicians.

From their library I particularly recommend the first article, below.  The last two are very technical but important new research.


Expectations of Pain: I Think, Therefore I Am, Jones-London M, National Institute of Neurological Disorders and Stroke

For pain mechanisms, read
Beyond Neurons: Evidence that Immune and Glial Cells Contribute to Pathological Pain States, Watkins L and Maier SF, Physiology Review. 2003;82:981-1011.

For pain mechanisms, read
Complex Regional Pain Syndrome (CRPS): Evidence of focal small-fiber axonal degeneration in complex regional pain syndrome-I (reflex sympathetic dystrophy),  Oaklander AL et al., Pain. 2006;120:235-243.

There is no link to the following double blind controlled research publication:

Mercadante S, Arcuri E, Tirelli W, Casuccio A. Analgesic effect of intravenous Ketamine in cancer patients on morphine therapy: a randomized, controlled, double-blind, crossover, double-dose study. J Pain Symptom Manage 2000;20:246-252. Mercadante et al compared intravenous infusions of Ketamine (0.25 and 0.5 mg/kg) with placebo in a double-blind, crossover study of 10 cancer patients with neuropathic pain.

Please note that the free Adobe Acrobat Reader is needed to read some references.

You can download the free reader now.

~~~~~The material on this site is for informational purposes only, and is not a substitute for medical advice, diagnosis or treatment provided by a qualified health care provider. ~~~~~

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