MONDAY, March 12 (HealthDay News) -- A U.S. Food and Drug Administration advisory panel recommended on Monday that the makers of a new class of painkillers be given a second chance to develop the powerful drugs, despite concerns about joint failures.

The expert panel voted 21-0 to allow three pharmaceutical companies to resume testing of their respective medications, albeit with safety precautions to help shield patients, the Associated Press reported.

"There's clearly a worrisome safety signal, but in spite of that I think there's an unmet need in certain patient populations," Mayo Medical School expert Dr. Sherine Gabriel, an advisor on the panel, told the AP.

Studies of these painkillers were stopped in 2010 after some osteoarthritis patients wound up needing knee replacement surgery while on the medications. At the time, Dr. Nancy Lane, lead researcher on one of those trials, said patients who ended up needing a new knee most likely harmed their damaged joint even further because the painkillers made them feel so good.

"They probably accelerated the degeneration of the joint," said Lane, director of the Aging Center, Medicine and Rheumatology, at the University of California, Davis. "Sometimes, pain is good in protecting you."

However, there was some evidence that when these drugs were given with another common painkiller, a reaction occurred that might have caused the problem.

In addition to tanezumab, which is made by Pfizer Inc., trials of two similar drugs were also stopped. These drugs were REGN475, made by Regeneron Pharmaceuticals, and fulranumab, made by Johnson & Johnson.

Now, the three companies hope to develop these drugs, known as anti-nerve growth factors (anti-NGFs), saying they are needed by many patients suffering from osteoarthritis. They propose to run trials using the drugs at lower doses and without other pain medications such as Advil. In addition, they have said they will be more selective in which patients they recruit for their research.

Dr. Elaine Tozman, an associate professor in the division of rheumatology and immunology at the University of Miami Miller School of Medicine, said she doesn't think the new painkillers would add much to the treatment of osteoarthritis.

"This is really a drug which is for a symptom of osteoarthritis, it's really for pain," she said. "As rheumatologists, most of us are looking for a drug that works on the underlying disease."

Tozman noted that patients with severe osteoarthritis of the knee usually go on to have a joint replacement.

The drug companies say there are millions of people who could benefit from these drugs.

"Based on the assessments of risk and benefit, we conclude that further clinical investigation of tanezumab in osteoarthritis and other forms of chronic pain is warranted with the protection of additional risk management and surveillance measures," Pfizer said in FDA briefing documents. "Chronic pain affects millions of adults in the United States. For many patients, treatment of chronic pain is inadequate in part due to the limitations in the availability of effective treatments and inadequate patient and clinician knowledge about the best ways to manage chronic pain."

For its part, Regeneron stated "... there may be a role for anti-NGF therapy in pain conditions where there is a high unmet need, i.e., those for which there are no adequate alternatives."

Although the FDA is not required to follow the recommendations of its advisory panels, it usually does.

Lane said tanezumab, which is given by injection, should probably not be used frequently. The effect of the drug can last at least eight weeks, she added, but no studies have been done yet on its long-term effects.

The drug works in a unique way by blocking nerve growth factor (NGF), which is essential for normal development of the nervous system but is also released when there is inflammation. NGF stimulates nerve cells and triggers pain, Lane explained.

"By inhibiting NGF, we really get a dramatic reduction in pain in patients who have pretty severe osteoarthritis," she said. "It doesn't do anything to the disease, it doesn't hurt your stomach, it doesn't change how you think or make you groggy. This is a real game-changer."

In addition to osteoarthritis, tanezumab was also being tested in patients with cancer pain, interstitial cystitis, chronic low back pain and diabetic nerve pain.

Some 27 million adults in the United States have osteoarthritis, with the knee being the most affected joint, according to the U.S. Centers for Disease Control and Prevention.

The number of people with osteoarthritis of the knee is expected to rise as baby boomers age and as obesity among Americans increases, Lane said.

More information

For more on osteoarthritis, visit the U.S. National Library of Medicine.