By Pat Anson, PNN Editor

A first of its kind study that compared four medications widely used to treat neuropathy found that all four were usually ineffective in treating pain and many patients stopped taking them due to side effects.    

Over 20 million people in the U.S. suffer from neuropathic pain, a tingling, burning or stinging sensation in the hands and feet caused by nerve damage. Neuropathy is often caused by diabetes, chemotherapy or trauma, but in about 25% of cases the cause is unknown and classified as cryptogenic sensory polyneuropathy (CSPN).

There is little guidance for physicians and patients on what drugs to take for CSPN, so researchers at the University of Missouri School of Medicine conducted a “real world” study in which 402 patients with CSPN took one of the four neuropathy medications.

The four drugs studied were nortriptyline (Aventyl), a tricyclic antidepressant; duloxetine (Cymbalta), a serotonin-norepinephrine reuptake inhibitor (SNRI) antidepressant; pregabalin (Lyrica), an anti-seizure drug; and mexiletine (Mexitil), an anti-arrhythmic medication used to treat irregular heartbeats.

Nortriptyline, duloxetine and pregabalin are approved by the FDA for treating neuropathy, while mexiletine is used off-label. None of the drugs were originally developed to treat neuropathic pain.

"As the first study of its kind, we compared these four drugs in a real-life setting to provide physicians with a body of evidence to support the effective management of peripheral neuropathy and to support the need for newer and more effective drugs for neuropathic pain," said lead researcher Richard Barohn, MD, executive vice chancellor for health affairs at the University of Missouri.

After 12 weeks of use, any drug that reduced pain for a patient by at least a 50% was considered effective, a recognized industry standard to define therapy success.. Researchers also kept track of patients who stopped taking a drug and dropped out of the study due to adverse effects.

The study findings, published in JAMA Neurology, can best be described as underwhelming. Patients were far more likely to stop taking a drug than they were to stay on a medication that was helping them.    

Of the four drugs, only nortriptyline was an effective pain reliever for at least 25% of patients. It also had the second-lowest drop-out rate (38%), giving it the highest level of overall utility. Duloxetine had the second-highest efficacy rate (23%) and the lowest drop-out rate (37%).

Pregbalin had the lowest efficacy rate (15%) and the second highest drop-out rate (42%), while mexiletine had the highest drop-out rate (58%) and an efficacy rate of 20 percent.

"There was no clearly superior performing drug in the study," Barohn said. "However, of the four medications, nortriptyline and duloxetine performed better when efficacy and dropouts were both considered. Therefore, we recommend that either nortriptyline or duloxetine be considered before the other medications we tested."

While nortriptyline had the highest efficacy rate, it also had the highest rate of adverse events, with over half of patients (56%) reporting side effects such as dry mouth, drowsiness, fatigue and bloating.  

Previous studies have found that duloxetine and pregabalin had higher efficacy rates for neuropathic pain, but Barohn and his colleagues say their research more accurately reflects what patients experience in real life and what physicians encounter in their practice.

“Our findings could affect how these 4 drugs are used by all physicians who treat patients with neuropathy. Findings support duloxetine and nortriptyline as better-performing drug choices in this population with neuropathic pain, suggesting that they should be prescribed before pregabalin or mexiletine are considered. However, this study also supports a finding that all 4 drugs helped improve pain in at least some patients, so each could be tried if others failed,” they concluded.     

There are several other drugs used to treat neuropathy, including gabapentin, venlafaxine and sodium channel inhibitors. Barohn says additional comparative studies should be performed on those drugs. His goal is to build effectiveness data on nearly a dozen drugs for CSPN.