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Neuropathic pain is relatively common and often poorly treated. Neuropathic pain is characterised by abnormal hypersensitivity to stimuli (hyperalgesia) and nociceptive responses to non-noxious stimuli (allodynia). Neuropathic pain can be a consequense of metabolic disorders, viral infections, and autoimmune diseases affecting the central nervous system (CNS)[1]. Neuropathic pain in the general population is estimated to have a prevalence ranging between 3% and 17%.
Currently existing therapies for neuropathic pain are far from effective. All current treatments are symptomatic rather than disease-modifying or curative. Only 40%–50% of patients reach the magic number of 30% pain relief in the clinical setting and 50%–60% of patients get no pain relief.[2] Often a combination of drugs are taken.
The management of neuropathic pain is challenging and, as with all pain, should be approached with a biopsychosocial framework. There are several options for drug treatment as part of an overall approach to improve patients’ quality of life and function.
Additionally a range of therapeutic modalities is emerging, targeting a variety of mechanisms, that may in the future have better client outcomes. eg. Nanotechnologies have enabled novel solutions for the treatment of various diseases. Nanodrug delivery systems present some advantages than conventional drug delivery systems such as high cellular uptake and reduced side effects[3]
Current Medication Recommendations
The below video gives a 12 minute overview of the state of play regarding Neuropathic pain medications
[4]Guidelines from different countries offer consistent recommendations for treating neuropathic pain. Effective first and second-line therapies include tricyclic antidepressants, duloxetine, venlafaxine, gabapentin, pregabalin and topical lidocaine[5].
The Special Interest Group on Neuropathic Pain 2019 recommended this approach for medication treating neuropathic pain[1].
Neurotoxin Botulinum toxin 25–300 U BTX-A 0.9% saline AE Pain at injection site
As a Physiotherapist it is important to be aware of which medications can impact on our patients safety, medication is obviously not within a physiotherapist job role specifically however knowing what the potential impact of some medications can be very valuable. See Medication and Falls, Medication and Older People to understand the risks associated with these medications, falls risk being a very important issue to be aware of.
Medications
Anti Epileptic Drugs (AEDs): AEDs are used extensively worldwide to treat a wide range of disorders other than epilepsy, such as neuropathic pain, migraine, and bipolar disorder. [6]The pathophysiological processes involved in neuropathy lead to is neuronal hyperexcitability. The main action of the AEDs is to decrease hyper excitability.
Antidepressants: Several antidepressants have been efficacious in the management of chronic neuropathic pain, including the tricyclic antidepressants. Tricyclic antidepressants may relieve neuropathic pain by their unique ability to inhibit presynaptic reuptake of the biogenic amines serotonin and noradrenaline, but other mechanisms such as N-methyl-D-aspartate receptor and ion channel blockade probably also play a role in their pain-relieving effect.[7]The selective serotonin reuptake inhibitors have either been less robust (paroxetine, citalopram) or lacked any efficacy at all (fluoxetine)[8]
Opiods: Often discouraged because of concerns about overdoses, abuse, dependence, and the effects of long-term use. High doses of opioids typically are needed to provide significant pain relief for neuropathic conditions[9]
Topical Treatments: Usually available as a patch, gel, or cream, topical treatments can be helpful for localized neuropathic pain. The medication is absorbed into the skin, either numbing the area or relieving pain. An option for individuals who cannot tolerate oral medication. Little of the medication reaches the bloodstream, so cognitive side effects are avoided. Multiple applications are typically needed for significant pain relief.[9]
Emerging Medications and Modes of delivery
Most of the available treatments for neuropathic pain have moderate efficacy and present side effects that limit their use. As such the need exists to identify new effective therapeutic strategies in neuropathic pain management. Some of the new approaches are listed below[1]
Several clinical trials have shown the potential effectiveness of cannabis-derived compounds in the treatment of pain associated with diabetes, chemotherapy, and multiple sclerosis.
Sativex already approved by the FDA for the treatment of spasticity in multiple sclerosis patients is considered as an alternative for patients suffering from neuropathic pain.
Nanotechnology-based drug delivery systems are promising tools to resolve the low solubility and the bioavailability of some compounds. The use of nano carriers could be an area of growth and clinical benefit.
Repurposing drugs currently approved for other indications that have already shown efficacy in animal models of neuropathic pain.
Conclusion
Neuropathic pain in the general population is estimated to have a prevalence ranging between 3% and 17%. Neuropathic pain management focuses on treating symptoms, and only in some pathological condition, the etiological causes can be treated relieving pain[6]. A range of therapeutic modalities is emerging, targeting a variety of mechanisms. In the near future we may be able to treat neuropathic pain in a more precise manner.
