Neurontin for Chronic Pain
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Neurontin Significantly Reduces Chronic Neuropathic Pain

SCARBOROUGH, ON -- Dec. 23, 1998 -- Two studies recently published in The Journal of the American Medical Association, report that Parke-Davis’ Neurontin(R) (gabapentin capsules) significantly reduced chronic neuropathic pain.

One study examined the effects of Neurontin on patients with diabetic peripheral neuropathy (DPN), a chronic, often painful condition that affects approximately half of the estimated 1.5 million diabetes patients in Canada. A companion study examined the use of Neurontin in patients suffering from post-herpetic neuralgia (PHN), the chronic neuropathic pain condition that can follow shingles (herpes zoster).

Results of the national, multi-centre DPN study demonstrated that patients suffering from diabetic peripheral neuropathy experienced a significant reduction in pain after treatment with the drug and that 26 percent of those patients treated with Neurontin were pain-free at the end of the trial compared to 15 percent of patients treated with placebo. This difference was statistically significant.

Findings of the national, multi-centre PHN study showed that patients suffering from the condition experienced a statistically significant reduction in average daily pain after treatment with Neurontin. Importantly, almost twice as many patients treated with Neurontin (16 percent) were pain-free versus those treated with placebo (8.8 percent) at the end of the trial. Both studies also showed that patients receiving Neurontin experienced improvement in sleep and overall quality of life.

The PHN study was a multi-centre, randomized, double-blind study conducted over a treatment period of eight weeks and involved 229 PHN patients.

"The results of this trial are particularly encouraging, given the hundreds of thousands of people suffering from this debilitating and extremely painful condition," said R. Norman Harden, M.D., director of the Centre for Pain Studies, Rehabilitation Institute of Chicago. "Further, the age distribution of patients with PHN includes a disproportionate number of older patients, which is a difficult population to treat."

PHN is a syndrome of often intractable pain following herpes zoster, a condition commonly known as shingles. It is estimated that 10 to 20 percent of Canadians will be affected by herpes zoster in their lifetime. In the majority of patients, the condition is characterized by intense pain that has been described by sufferers as burning, deep aching, tearing and electric shock-like. While the pain tends to fade over a period of time, as many as 15 percent suffer from chronic neuropathic pain that persists beyond the resolution of the herpes zoster rash. Pain that persists for three months after resolution of this rash is commonly defined as PHN. PHN may persist for years in some patients.

The DPN study was a randomized, double-blind, placebo-controlled trial conducted over a treatment period of eight weeks involving a total of 165 patients. The patients enrolled had a one to five-year history of pain associated with diabetic neuropathy.

"DPN is a neuropathic condition that is, historically, extremely difficult to treat," said Keith R. Edwards, M.D., director, Neurological Research Centre, Bennington, VT. "This study is one of the largest of its kind in this condition. In patients with DPN, gabapentin substantially reduced neuropathic pain and was well tolerated.

“Further, more significant pain reduction was observed in some patients after only two weeks of treatment. All of these findings combined are clinically important."

DPN is characterized by nerve fibre loss that can result in symptoms ranging from diminished pain and temperature perception, paresthesia (pins and needles) and neuropathic (sharp or burning) pain, to loss of light touch and muscle weakness. Other symptoms include insomnia, anxiety, depression, weight loss and a general decline in quality of life.

"In this study, Neurontin reduced pain and sleep interference associated with the condition and also exhibited positive effects on mood and quality of life," Dr. Edwards said.

Diabetes is a clinical condition that impairs the ability of the body to produce or properly respond to insulin, a hormone essential for life. Type II diabetes, also known as adult onset or non-insulin-dependent diabetes (despite the fact that many require insulin injections) usually occurs in those over 45 and overweight. Type II diabetes affects the majority of the 1.5 million Canadian diabetics and it is estimated that another 750,000 people are undiagnosed. Type I diabetes, also known as juvenile onset or insulin-dependent diabetes usually starts in children or young adults who are slim and affects about 10 per cent of people with diabetes in Canada.

The pain associated with DPN in diabetic patients is, at times, constant, severe and deep, and is frequently associated with mood and sleep disturbances as well as a decline in function. Pain in diabetic patients with DPN affects the feet and ankles most often and, to a lesser extent, the lower extremities above the knees and upper extremities.

Neurontin is indicated as adjunctive therapy in the treatment of partial seizures with and without secondary generalization in adults (greater than 12 years old). Neurontin is contraindicated in patients who have demonstrated hypersensitivity to the drug or its ingredients.

The most common adverse events during clinical trials were somnolence (19.3 percent versus 8.7 percent with placebo); dizziness (17.1 percent versus 6.9 percent with placebo); ataxia (12.5 percent versus 5.6 percent with placebo); fatigue (11 percent versus five percent with placebo); nystagmus (8.3 percent versus four percent with placebo); and tremor (6.8 percent versus 3.2 percent with placebo).