Diabetic painful neuropathy: current and future treatment options

Diabetic painful neuropathy (DPN) is one of the most common causes of neuropathic pain. The management of DPN consists of excluding other causes of painful peripheral neuropathy, maximising diabetic control and using medications to alleviate pain. The precise relationship between glycaemic control and the development and severity of DPN remains controversial. In this context, drugs such as aldose reductase inhibitors, ACE inhibitors, lipid-lowering agents and alpha-lipoic acid (thioctic acid) may have a useful role to play. There is also evidence that a successful pancreatic transplant may improve symptoms over time, but the mainstay of management continues to be symptomatic control of pain with drugs. Evidence from placebo-controlled studies has shown that opioids, antiepileptic and antidepressant drugs together with capsaicin are effective for alleviating DPN. Tramadol and oxycodone have been shown to be effective in studies of limited duration but their adverse effects, such as constipation and physical dependency, may limit their usefulness as a first-line treatment for DPN. Of the antidepressant drugs, the tricyclic antidepressants have been shown to be effective for alleviating DPN. These medications are widely used but their anticholinergic and sedative properties may not be well tolerated by patients. There is also good evidence that the serotonin-noradrenaline reuptake inhibitor antidepressant drugs venlafaxine and duloxetine are effective for treating DPN. However, venlafaxine may cause cardiac dysrhythmias, and patients using this medication require careful cardiac monitoring. Duloxetine appears to be less cardiotoxic and is licensed in the US and EU for alleviating DPN. The gabapentinoid group of drugs, gabapentin and pregabalin, appear to be the most evidence-based of the antiepileptic drugs for treating DPN. Large placebo-controlled studies have been performed with both of these agents. For many patients, it is still unclear what advantages pregabalin has over gabapentin for DPN. Until better evidence emerges, the potential availability of less expensive generic formulations of gabapentin, together with greater experience with its use, favour gabapentin as the main antiepileptic drug for alleviating DPN. Topiramate, lamotrigine, sodium valproate and oxcarbazepine have been shown to be effective in smaller studies but do not have the same evidence base as the gabapentinoid group of drugs. Of the newer antiepileptic drugs, lacosamide appears to be the most promising for alleviating DPN. Capsaicin has the best evidence base of all the topical agents, but local anaesthetic patches may also have a useful therapeutic role. It is not possible to nominate a single drug as the first-line treatment for DPN and there is evidence that a low-dose combination of two or more drugs rather than a single agent may provide better symptomatic relief with fewer adverse effects. Further studies are necessary to clarify the best combination(s) of treatment for DPN.