CHICAGO -- New studies show that an epilepsy drug can bring relief to diabetics who suffer pain from nerve damage and to people with shingles who develop nerve pain that sometimes lasts for years.
The two types of nerve pain afflict at least hundreds of thousands and possibly millions of Americans.In the new studies, the drug gabapentin (marketed as Neurontin) worked as well as the usual drugs prescribed for such nerve pain -- tricyclic antidepressants -- have worked in past studies, researchers said.
They did not directly compare the drugs in the findings published in today's edition of The Journal of the American Medical Association.
Both studies were funded by Neurontin maker Parke-Davis, a division of Warner-Lambert Co., Morris Plains, N.J.
Gabapentin costs much more but many patients can't take antidepressants for medical reasons or they find the side effects intolerable, said experts not involved in the research.
After gabapentin was approved to control epileptic seizures in 1994, doctors quickly discovered that it also relieved nerve pain, said one expert, Dr. Phillip A. Low, a neurology professor at the Mayo Clinic in Rochester, Minn.
Shingles is an infection by the chicken-pox virus of nerves supplying certain areas of the skin, usually in people over 50. It causes severe pain that has been described as tearing, burning, piercing and "electric shocklike." Shingles usually produces a rash and goes away, but for 10 to 20 percent of sufferers, the aftermath is pain that can last for years, researchers say.
For such pain, tricyclic antidepressants provide relief in only about half of cases, so gabapentin may be a better first choice, Low and a colleague, Dr. Rose M. Dotson, wrote in an editorial accompanying the studies.
For diabetic nerve pain, tricyclics are still probably a better first choice, since they are less expensive and doctors have more experience with them, the editorial said, adding that further research is needed.
Nerve pain is one of the most common and difficult types of pain to treat, Low and Dotson wrote.
Gabapentin is one of several seizure-controlling medicines that doctors have discovered can relieve it, even though none is approved to be marketed for that purpose.
Seizure-controlling drugs and the tricyclics all modify brain chemicals that regulate pain signals from nerves, Low and Dotson said.
But the tricyclics can cause heart rhythm problems, low blood pressure, grogginess, dry mouth, constipation, confusion and urinary retention -- side effects that are dangerous in some patients and intolerable in others, Low and Dotson said.
Gabapentin caused far fewer side effects in the new studies, though some patients stopped taking it because of drowsiness or dizziness, researchers said.
In one study, led by Dr. Miroslav Backonja of the University of Wisconsin, Madison, 70 patients with diabetic nerve pain who were randomly assigned to receive gabapentin for eight weeks had significantly less pain and better sleep than 65 patients who were given a placebo. Patients were studied at 20 different sites and did not know whether they received the drug or the dummy pill.
In the other study, led by Dr. Michael Rowbotham of the University of California, San Francisco, similar differences were found among 89 patients given gabapentin and 95 given placebos for four weeks at 16 study sites to treat pain syndromes following shingles.