The advisers to the U.S. Food and Drug Administration voted 21-0 that the agency should lift its hold on clinical trials of the drugs, from the class of anti-nerve growth factors.

The FDA is not required to follow panel recommendations, though it often does, and will make a final decision later.

The FDA halted almost all clinical trials of the drugs in 2010 after nearly 500 people taking the drugs in studies had to have joints replaced.

Pfizer, Regeneron, and Johnson & Johnson are now pitching to resume wider trials, in what could be a multi-billion-dollar pain market.

The FDA advisers said the drugs provide a meaningful benefit to help people treat pain, many of whom may not have other options. They said companies should try to figure out which patients would benefit most, and perhaps try to exclude those who may be predisposed to joint problems.

"I think we can't close the door ... for this class of drugs because it is unique, and it has been shown to be effective," said Susan Broyles, the patient representative on the panel.

Companies have studied the drugs 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 work by blocking a protein called nerve growth factor that is associated with nerve pain. They have the potential to become the first biotechnology drugs specifically for 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 last week ahead of the panel discussion.

Pfizer was furthest along in development of its biotech anti-nerve growth factor 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.

"Physicians and patients are in need of options for difficult-to-treat pain conditions and the panel's vote today is an important step towards helping us more fully understand the benefit-risk profile of this important new class of medicines," said Steve Romano, a senior vice president at Pfizer.

Before the trials were halted, analysts had projected peak global sales for tanezumab above $1 billion a year.

(Reporting by Anna Yukhananov in Washington; editing by Carol Bishopric)

• A Permanent Economic Emergency