Neuropathic Pain Medications – review & metanalysis of 229 studies

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Pharmacotherapy for neuropathic pain in adults:

a systematic review and meta-analysis (pdf)

 

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This review was done by many of the best pain specialists from all over the world. You will not find answers in that large review if neuropathic pain has already failed tricyclic antidepressants (Elavil, amitriptyline, Norpramin desipramine, others), gabapentin (Neurontin), pregabalin (Lyrica), lidocaine, capsaicin, or opioids. That is the current paradigm. A new paradigm – glial modulators  – that I discuss on this site, may or may not give relief.

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A member of the International Association for Study of Pain, IASP, published a brief critique of that comprehensive review of 229 trials of medications for neuropathic pain published in Lancet Neurology February 2015. The critique is posted below, done by a member of the Neuropathic Pain Special Interest Group, NeuPSIG.

 

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To understand the metanalysis of these 229 trials, you need to understand the simple concept of number needed to treat, NNT.

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NNT is an estimate of “the number of patients that need to be treated in order to have an impact on one person.”

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The smaller the number, the more effective the drug. Example, NNT of 7.2 for gabapentin means you need to treat  7.2 people before a response. If 3, need to treat 3 before a response.

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Barsook (Harvard, ref. below) reviewed ketamine studies in 2009:  “they did show a level of efficacy (of ketamine) based on NNT that equals or betters most drug trials for this condition.”

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“NeuPSIG has just published an up to date systematic review on the effectiveness of pharmacotherapy in Lancet Neurology. They have negotiated with the journal to make it available beautifully open access. You can download it for free here.”

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Neil O’Connell, Brunel University London

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“This is a comprehensive review, containing 229 trials of the full range of pharmacological agents using robust methods, to synthesize, summarise and make value judgements about the quality of the available evidence. So what are the take home messages?”

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“Using a primary outcome of achieving at least 50% pain relief trial outcomes were described as “generally modest”. The number of patients needed to treat with the drug compared to a placebo for one more person to achieve this outcome ranged from a relatively rosy 3.6 (95% confidence interval 3 to 4.4) for tricyclic antidepressants such as amitryptiline, 4.3 (95%CI 3.4 to 5.80 for strong opioids to a less impressive 7.2 (95%CI 5.9 to 9.21) for gabapentin, and 7.7 (6.5 to 9.4) for pregabalin (often sold under the brand-name Lyrica). It’s interesting, at least to me, how much better the older more traditional agents seem to have fared compared on effectiveness to the more modern (and commonly more expensive) agents although the safety and tolerability of gabapentin seems superior.”

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“The spectre of publication bias also raises its head. The reviewers carefully took a number of routes to try to unpick this notoriously difficult issue and estimate that there has been overall a 10% overstatement of treatment effects. Published studies reported larger effect sizes than did unpublished studies. This is not a problem restricted to the field of pain trials. It is a burning issue across the world of clinical trials. It is very important because if we fail to base our clinical recommendations on the totality of relevant evidence (because some data are hidden from us) we are in danger of mis-estimating the benefits and the harms and as a result patients are put at risk. If you think that is pretty important then there are ways that you can help. Check out the All-Trials campaign.”

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“Overall what does this mean? Many drugs are effective but not as effective as we would wish them to be. No pharmacological agent really impresses and for any drug the most probable outcome is failure to produce 50% pain relief. There are various potential reasons for this. The first is that the drugs may only be moderately or marginally effective, another is that neuropathic pain includes quite a mixed bag and our ability to accurately diagnose and to target drugs to specific mechanisms in the clinic is currently fairly poor.”

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“The NeuPSIG review team formulate a number of recommendations for revision of their clinical guideline for managing NP pain, balancing the benefits, harms, costs and strength of the evidence.”

• a strong recommendation for use and proposal as a first-line treatment in neuropathic pain for tricyclic antidepressants, serotonin-noradrenaline reuptake inhibitors, pregabalin, and gabapentin;

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• • a weak recommendation for use and proposal as a second line treatment for lidocaine patches, capsaicin high-concentration patches, and tramadol; and a weak recommendation for use and proposal as third line for strong opioids and botulinum toxin A. Topical agents and botulinum toxin A are recommended for peripheral neuropathic pain only.

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“This email [from IASP’s NeuPSIG] is also published as a blogpost at www.bodyinmind.org”

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References

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Finnerup NB, Attal N, Haroutounian S et al. Pharmacotherapy for neuropathic pain in adults: a systematic review and meta-analysis. Lancet Neurol. 2015;14:2:162-73.

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Glial modulators – another paradigm

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From my January 2012 brief review of publications on ketamine, only one of a handful of glial modulators, this author says reviews “show a level of efficacy based on NNT that equals or betters most drug trials for this condition.”

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Ketamine and chronic pain – Going the distance, David Barsook, Director, P.A.I.N. Group, Massachusetts General, McLean and Children’s Hospitals, Harvard Medical School, Boston, MA;

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This paper covers essential points not mentioned by many, thus quoted at length below:

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Our current therapeutic armamentarium is quite limited in terms of analgesic efficacy in controlled trials. Some would argue that the small efficacy (both at a population level and the magnitude of change in VAS score) this is related to the fact that we need to consider mechanistic approaches to chronic pain subgroups. However, patients and clinicians find themselves in a position of “what to do now”.

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Ketamine, brain function and therapeutic effect – neuroprotective or neurotoxic

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With the onset of chronic pain (including CRPS) a number of changes in brain function occur in the human brain including but not limited to: (1) central sensitization ; (2) functional plasticity in chronic pain and in CRPS; (3) gray matter volume loss in CRPS ; (4) chemical alterations ; and (5) altered modulatory controls. Such changes are thought to be in part a result of excitatory amino acid release in chronic pain. Excitatory amino acids are present throughout the brain and are normally involved in neural transmission but may contribute to altered function with excessive release producing increased influx of calcium and potentially neural death. Here lies the conundrum the use of an agent that potentially deleteriously affect neurons that may already be compromised but may also have neuroprotective properties by mechanisms that include reducing phosphorylation of glutamate receptors resulting in decreased glutamatergic synaptic transmission and reduced potential excitotoxicity . Alternatively, ketamine may affect glia regulation of glutamate and inhibit glutamate release within glia. However, by whatever mechanism ketamine acts on CRPS pain, there does seem to be a dose/duration effect in that longer doses at levels tolerated by patients seem to prove more effective in terms of the duration of effects.

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So what could be happening in the brain and what is required to alter brain systems and reverse the symptomatic state? Ketamine may diminish glutamate transmission and “resets” brain circuits, but it seems that a minimal dose and/or duration of treatment is required. Alternatively, ketamine may produce neurotoxicity and damage or produce a chemical lesion of affected neurons. These two issues are important to be understood in future trials. Reports from patients who have had anesthetic doses have included prolonged pain relief for many months. While the authors did not address issues such as the effect of dosing duration or repetitive dosing at say 6weeks, they did show a level of efficacy based on NNT that equals or betters most drug trials for this condition.”

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Conclusions

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As a community we have a major opportunity to define the efficacy and use of a drug that may offer more to CRPS (and perhaps other) patients than is currently available. This is clearly an opportunity that needs urgent attention and a number of questions remain to be answered. For example, is ketamine more effective in early stage disease? How does ketamine provide long-term effects? Further controlled trials evaluating dose, duration, anesthetic vs. non-anesthetic dosing are needed. Few of us really understand what it is like to suffer from a chronic pain condition such as CRPS. Ketamine therapy may be a way forward that can be brought into our clinical practice through further controlled studies that will allow for appropriate standards for use in patients.

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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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Please understand that it is not legal for me to give medical advice without a consultation.

If you wish an appointment, please telephone my office.

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