NEW YORK (Reuters) - Depomed Inc. (DEPO.O: Quote, Profile, Research) shares rose 10 percent after it reported its experimental pain drug proved safe and effective in treating nerve pain caused by shingles in a mid-stage clinical trial, and said it would begin pivotal late-stage trials in the first half of this year.

The drug, Gabapentin GR, is an extended-release version of Pfizer Inc.’s (PFE.N: Quote, Profile, Research) pain and epilepsy medicine Neurontin, which is now available in less expensive, generic forms.

In the four-week, 158-patient study, Gabapentin GR taken twice daily proved to be significantly better than a placebo in reducing pain associated with shingles, or herpes zoster, viral infection, the company said.

A once-daily dose of the drug failed to achieve statistical significance over a placebo in treating the condition known as postherpetic neuralgia.

Both Gabapentin groups in the study received 1,800 milligrams of the drug per day. The company declined to disclose how the dose was split in the twice-a-day group.

There were no serious adverse events associated with Gabapentin GR, the company said. The most common side effect was dizziness, which is commonly associated with Gabapentin.

Postherpetic neuralgia is a persistent pain condition caused by nerve damage during a shingles episode. The pain associated with the condition can be severe and last for months.

“These data strongly support twice-daily Gabapentin GR and are very encouraging for once-daily use for the treatment of postherpetic neuralgia,” Depomed Chief Executive John Fara said in a statement.

Shares of Depomed were up 60 cents at $6.53 on Nasdaq.

The promotion of off-label uses of pharmaceuticals has gotten other drug companies in trouble. In 2004, Warner-Lambert pleaded guilty to federal charges that it promoted epilepsy drug Neurontin for off-label uses beginning in the 1990s. Pfizer Inc., which acquired Warner-Lambert in 2000, agreed to pay $430 million to resolve criminal charges and civil liabilities in the case.

Neurontin is an anti-convulsant drug prescribed to patients with epilepsy.

Wikipedia says: Gabapentin (Neurontin) is an anticonvulsant medication indicated in the treatment of epilepsy and neuropathic pain. It is also used in the treatment of bipolar disorder and may be effective in reducing pain and spasticity in multiple sclerosis.

NEURONTIN is an FDA-approved oral medication for management of postherpetic neuralgia (PHN). PHN is the pain that lasts one to three months after shingles has healed. In studies of PHN, NEURONTIN greatly reduced patients’ pain.

NEURONTIN is also FDA approved for the treatment of partial seizures in adults and children.

NEURONTIN may begin to work as early as 1 week after you start treatment. For some people, it may take longer to work. For others, the pain may not get better.