It looks like the anti-nerve growth factors might be able to re-emerge from the Food and Drug Administration clinical-hold graveyard. An FDA advisory panel recommended yesterday that the drugs are worth pursuing further despite the fact that osteoarthritis patients saw a higher rate of joint problems -- the very side effect that landed them on the FDA's naughty list.

The big question: What the heck took so long? The FDA put the first clinical hold on Pfizer's (NYSE: PFE) tanezumab in June 2010 and halted the other anti-nerve growth factors being developed by Regeneron Pharmaceuticals (Nasdaq: REGN), Sanofi (NYSE: SNY), AstraZeneca (NYSE: AZN), and Johnson & Johnson (NYSE: JNJ) by the end of that year. I'm all for keeping patients safe, but an earlier consult of the advisory panel sure would have been helpful for the companies and their investors -- it's not like the patent clock stops when drugs are put on clinical hold.

The FDA doesn't have to follow the advice of the panel of outside experts, but with such an overwhelming majority saying the anti-NGF drugs are worth pursuing, I'd have a hard time seeing the FDA continuing their hard-line stance. The FDA will likely put some restrictions on the trials when they resume, such as not taking the anti-NGF drugs with another class of pain relievers and pulling patients off the drugs early if it appears they aren't working.

Coming off a clinical hold is a necessary first step to getting the drugs approved, but Pfizer and friends aren't out of the woods yet. Efficacy data on tanezumab, the furthest along of the anti-NGF drugs, looks pretty good. There was even a theory that the pain was relieved so much in the osteoarthritis patients that they were overusing their joints, which was causing the apparent side effect. But the risk-benefit analysis -- always a subjective decision by the agency -- can only be determined when all the data is in.

Given their history, if tanezumab or the other drugs get approved, they'll likely only be used as a second- or third-line therapy when other pain medications aren't working. There's money to be made as a last-resort treatment, but not at the blockbuster levels expected a few years ago.

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