Chronic Nerve Pain Responds to Epilepsy Drug

Gabapentin Provides a New Treatment Option
By Sally Squires - Washington Post Staff Writer
Tuesday, December 8, 1998; Page Z11

A drug for epilepsy is showing promise as an important new treatment for the chronic nerve pain suffered by many people with diabetes and by those experiencing the aftermath of shingles.

That result came in two separate studies published last week in the Journal of the American Medical Association (JAMA). Both studies were supported by Parke-Davis, a division of the Warner-Lambert Co. that manufactures the drug, gabapentin, under the trade name Neurontin.

Estimates are that 16 million people in the United States have diabetes. About half of people who have diabetes for 15 years or more develop chronic nerve pain--a condition called diabetic neuropathy--that can be very difficult to control.

The common infection shingles, caused by the virus herpes zoster, strikes 1 million people annually and also causes chronic pain in about 15 percent of patients. Known as post-herpetic neuropathy, this condition is also difficult to treat.

In shingles, the nerves are damaged by the herpes zoster virus. In diabetes, high levels of blood sugar are believed to gradually damage the nerves--one reason why doctors encourage people with diabetes to keep blood sugar levels tightly controlled.

Antidepressants are the standard treatment for both types of neuropathies. But those drugs, which can cause irregular heartbeat, sedation, confusion, precipitous declines in blood pressure and other complications, control pain in only about half of patients.

Several groups of researchers are seeking better ways to control these types of chronic nerve pain.

In one eight-week study reported in JAMA, researchers at the Pain Clinical Research Center at the University of California, San Francisco, randomly assigned 229 people with post-shingles pain to receive either gabapentin or a placebo, a harmless, nonmedicated preparation. Neither researchers nor the patients knew who received gabapentin until after the study ended.

Participants in the study were also evaluated using an 11-point pain scale. Patients who were already taking either narcotics or antidepressants continued taking those drugs during the study.

People who received gabapentin had a 33 percent reduction in average daily pain scores compared with an 8 percent decrease in the placebo group. Nearly half--43 percent--also reported that their pain was much or moderately improved compared with 12 percent of the people in the placebo group.

Mood, quality of life and sleep also improved for the gabapentin group versus those who took placebos. Sixteen percent of people who took gabapentin were pain-free at the end of the study, compared with 9 percent of those who took the placebo.

Based on the findings, the study's lead author, Michael Rowbotham, and his colleagues concluded that gabapentin "can be added to the list of first-line medications" for the treatment of chronic pain caused by shingles.

Gabapentin also proved effective in controlling chronic nerve pain in people with diabetes, according to a multi-center study. The team of scientists, led by researchers at the University of Wisconsin at Madison, randomly assigned 165 people to receive either gabapentin or a placebo. Neither the participants nor the researchers knew until the study ended which patients received the drug.

All participants in the study had experienced chronic nerve pain for at least one year and some had suffered as long as five years. They took either gabapentin or the placebo daily for eight weeks.

The study found a significant improvement in pain among participants in the gabapentin group compared with those who received the placebo. People who received the drug also reported sleeping better and said that their overall quality of life had improved.

Twenty-six percent of those treated with gabapentin were pain-free at the end of the study compared with 15 percent of those who received a placebo.

In an editorial accompanying the papers, Phillip A. Low and Rose M. Dotson of the Mayo Clinic noted that antidepressants should still be the first line of treatment for people with chronic nerve pain associated with diabetes because of their low cost and effectiveness in about 50 percent of patients. But they concluded that gabapentin should be the first line of treatment for people with diabetes who also have heart disease, irregular heartbeats or problems with low blood pressure, since they are at increased risk of complications if they take antidepressants.

Based on the new findings, Low and Dotson concluded that gabapentin is also a better choice for those suffering the lingering pain of shingles. Although gabapentin has never been tested head-to-head against the antidepressants, Low and Dotson said that gabapentin is the first choice for therapy because it has "fewer adverse effects."

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