FDA asks experts if pain drugs get second chance WASHINGTON (Reuters) - U.S. drug regulators are asking experts for advice on whether companies should restart clinical trials for painkillers that help people with osteoarthritis and other conditions, but can destroy joints. The U.S. Food and Drug Administration said these drugs, from the class of anti-nerve growth factors, represent a potentially significant and novel strategy for the treatment of pain," in a memo posted online on Thursday. However, the FDA put a hold on almost all clinical trials of the drugs in 2010 after nearly 500 people taking the drugs in studies had to have their joints replaced. Companies were allowed to keep testing the drugs in terminal cancer patients who had severe pain in their bones, since the benefits there may outweigh risks. Pfizer Inc, Regeneron Pharmaceuticals Inc and Johnson & Johnson are now pitching to resume wider trials, in what could be a multi-billion-dollar pain market. Outside advisers to the FDA will vote on Monday on whether there is a way for trials to move forward, perhaps by limiting the drugs to lower doses, or to only certain conditions where people have fewer treatment options. The drugs have been studied for common conditions like low back pain and osteoarthritis, or damage to the joints caused by wear and tear. The condition affects about 27 million adults in the United States and is a common cause of chronic disability. The drugs have also been tested in narrower groups, like people with bladder pain syndrome. The drugs block a protein called nerve growth factor (NGF) that is associated with nerve pain. However, NGF may also help with wound repair and the growth of new blood vessels, the FDA said. The joint problems with the drug may be because it blocks these beneficial effects of the growth protein, one FDA reviewer said. Pfizer was furthest along in development of its biotech anti-NGF drug, tanezumab, when the FDA asked it to halt trials in June 2010 because of the joint problems. Pfizer had already reported positive data for the medicine. We've had strong results from the clinical program. That's why we're so interested in progressing these compounds forward," Pfizer said in an interview on the advisory meeting. They have the promise of offering chronic pain patients something they haven't had in the past." Before the trials were halted, analysts had projected peak global sales for tanezumab above $1 billion a year. The anti-NGF drugs have the potential to become the first biotechnology drugs specifically for pain. Several injectable biotechnology medicines are used to treat rheumatoid arthritis, a potentially crippling immune system disorder. More traditional oral pain killers, such as aspirin, ibuprofen and Pfizer's own Celebrex, are typically used to treat osteoarthritis, but may have side effects such as promoting bleeding.