Laird Harrison

May 24, 2012

May 24, 2012 (Honolulu, Hawaii) — Patients prescribed once-a-day gabapentin for postherpetic neuralgia will usually get relief in the first 4 days — or not at all, a new study shows.

Even when it does work, the once-daily formulation of gabapentin (G-GR, Gralise, Depomed) provides only modest relief from postherpetic neuralgia, the pain that sometimes lingers after patients have recovered from herpes zoster or shingles, studies show.

In a separate phase 3 trial, patients taking the drug got about a half a point greater improvement on the Brief Pain Inventory (BPS) scale than patients taking a placebo, researchers report.

Both studies were reported here at the American Pain Society (APS) 31st Annual Scientific Meeting.

Difficult to Treat

Postherpetic neuralgia is difficult to treat, so physicians may keep prescribing a drug in the hope it will eventually kick in, said Mark Jensen, PhD, a professor of rehabilitative medicine at the University of Washington, Seattle. "But you don't want to give a drug for months and months."

So he and his research team set out to measure how quickly the benefits of a once-daily version of gabapentin could be observed in a study funded by Depomed.

They analyzed data from two 11-week randomized trials in which 357 patients took gabapentin and 364 took a placebo once a day.

Prescribers titrated the dose over 2 weeks, starting with 300 mg and working up to 1800 mg. Patients recorded their pain intensity on the Numeric Pain Rating Scale (NPRS), with 0 = no pain and 10 = worst possible pain.

The researchers defined the onset of response as the first of 2 consecutive days with a statistically significant (P < .05) greater reduction in pain.

They found that patients reached this end point on the second day after they started taking the drug or placebo. At that point, the gabapentin group reported a 6.7% reduction in pain scores while the placebo group reported a 1.7% drop (P = .0043).

The difference between the 2 groups widened slightly over the course of about a month, then began to narrow again.

At the 10th week, the gabapentin group said their pain had improved by 37% while the placebo group said their pain had improved by 29% (P = .0025).

In absolute scores this meant an improvement of 2.4 points for the gabapentin group and 1.9 points for the placebo group (P = .002). The improvement in the gabapentin group of 2 points on a 10-point scale is greater than the amount deemed by experts and patients to be clinically meaningful.

Dr. Jensen cautioned that he could not give medical advice because he is not a physician. But he concluded from the study that the benefits from the drug can appear quickly, although he also warned that some patients can be "late responders," and for them the benefits may take 5 or more weeks to emerge.

Brief Pain Inventory

In a separate study reported at the same meeting, researchers reported similar results in pain relief on a different scale, the Brief Pain Inventory.

On this scale, patients rate the intensity of 4 kinds of pain — worst, least, average, and current — on a scale of 0 to 10. They similarly rate the extent to which pain has interfered with their daily activities, including mood, walking ability, normal work, relationships, sleep, enjoyment of life, and general activity.

The researchers, with first author Michael Sweeney, MD, from Lifetree Clinical Research in Salt Lake City, Utah, randomly assigned 351 patients to the gabapentin group, and 361 to the placebo group. Patients rated their pain at baseline and 10 weeks.

After 10 weeks the patients taking the placebo reported that their worst pain improved by about 2 points, and those taking the gabapentin improved by about 2.5 points (P < .01 - .05). Changes in average and current pain were similar, and changes in least pain were slightly less.

The interference scales showed a trend toward improvement vs placebo, with improvements ranging from almost 1 to 2.5 for the drug and almost 1 to less than 2 for the placebo. The average difference in improvements on these scales was just below statistical significance (P < .059).

Gabapentin is a good drug for those who respond to it, Lin Tchia Yeng, MD, PhD, a professor of physical and rehabilitative medicine at the University of São Paulo, Brazil, told Medscape Medical News.

"It has been around for a long time," said Dr. Yeng, who was not involved in either study. "What's new is the once-a-day preparation. Normally it's 3 times a day. The new preparation can increase adherence, so it will help. And it has less side effects."

In Dr. Jensen's study, 54% of the patients who took gabapentin experienced adverse events, compared with 42% of the patients who took the placebo. Serious adverse events affected 1.9% of the gabapentin patients and 2.7% of the placebo patients.

Dr. Jensen disclosed that he works as a consultant to Depomed. Dr. Yeng has disclosed no relevant financial relationships.

American Pain Society (APS) 31st Annual Scientific Meeting. Abstract #380 and #376. Presented May 17, 2012.

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