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The study, appearing in the April 3 issue of the Journal of the American Medical Association, tested Cymbalta on patients with chronic cases of chemotherapy-related peripheral neuropathy -- pain, tingling and numbness in the limbs that arises when certain chemo drugs damage the nerves.
Of 115 patients who took the antidepressant for five weeks, 59 percent got some degree of pain relief, compared with 38 percent of patients given a drug-free placebo.
Researchers said the findings support what some doctors have seen in everyday practice, since Cymbalta is already used to treat the chemo side effect.
That use has been based on the fact that Cymbalta helps with other types of pain, said Dr. Michael Stubblefield, who was not involved in the study but treats patients with chemo-induced peripheral neuropathy at Memorial Sloan-Kettering Cancer Center in New York City.
Until now, cancer specialists have had to "steal" from evidence that Cymbalta helps with those forms of nerve pain, Stubblefield said.
"This is the first study of its kind to show that this works against chemotherapy-related neuropathic pain," he said.
It is estimated that 20 percent to 40 percent of patients treated with certain cancer drugs -- including so-called taxanes and platinums -- will develop peripheral neuropathy. For most, the problem improves once their chemo is over, said Ellen Lavoie Smith, the lead researcher on the study. But for some, she added, the nerve pain becomes chronic -- lasting for months or years after their chemo ends.
"This study focused on those patients," said Smith, an assistant professor of nursing at the University of Michigan School of Nursing, in Ann Arbor.
"The findings show that there is a medication that may be effective for reducing their pain from neuropathy," Smith said. But, she added, it didn't help everyone; the majority of Cymbalta patients improved, while others saw no change -- and 10 percent got worse.
The study included 231 patients with nerve pain that had persisted for at least three months since their chemo regimen ended. Half were randomly assigned to take Cymbalta for five weeks, while the other half took placebo pills. The two groups then switched treatments. None of the patients knew when they were taking the real drug and when they were on the placebo.
Of the patients given Cymbalta first, the average pain score fell by a point on a scale of 0 to 10. That's considered to be a "clinically important" change, Smith said, meaning it's an improvement patients notice in their daily lives.
The Cymbalta patients were also twice as likely to have a 50 percent decrease in pain scores versus the placebo users, and overall they reported improvements in their daily functioning and quality of life.
It is not clear how the antidepressant helps with nerve-related pain, but it is thought to act on certain brain chemicals involved in transmitting pain signals.
The findings are encouraging, Stubblefield said. But, like Smith, he pointed out that not everyone responds to Cymbalta. "This doesn't mean I'll be putting all my patients on it," he said.
There are other treatments for chemo-related pain -- although they have not yet been shown to work in rigorous clinical trials. One option, Stubblefield said, is Lyrica (pregabalin), which is another drug approved to treat other forms of nerve-damage-related pain.
Stubblefield said Lyrica tends to have fewer side effects than Cymbalta, and at least some patients may be able to tolerate it better. Cymbalta's side effects include fatigue, insomnia and nausea, which were reported by 5 percent to 7 percent of patients in the current study.
On the other hand, Stubblefield said, if a patient with nerve pain is also feeling depressed, it makes sense to try Cymbalta first.
There's also cost. Cymbalta is not yet available as a generic, and runs close to $200 a month. It is scheduled to lose patent protection at the end of 2013, so cheaper versions may become available.
Smith said there are still many questions to sort out: How well can patients tolerate Cymbalta over a longer term? Does the drug help nerve pain in patients who are still on chemo?
"We anticipate that it would help," Smith said. "But to what degree? Would it be enough to make a difference in their lives?"
As better treatments are helping more cancer patients survive, chronic peripheral neuropathy is emerging as one of the most difficult side effects of the treatments, said Dr. Sandra Swain, president of the American Society of Clinical Oncology.
Even minor actions, like picking up your keys, become difficult, Swain said. "It really affects your everyday living," she said.
Swain said the bottom line for patients is that "this drug may actually work, and it's something you can discuss with your doctor."
Still, Swain added, more research is needed -- not only into Cymbalta, but into other treatments for chemo-related pain.
Eli Lilly, the company that makes Cymbalta, provided the drug for the study. The work was funded by government and non-profit grants, and none of the researchers reported financial ties to Eli Lilly.
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