Pfizer s novel pain reliever tanezumab may work too well. Researchers write in Wednesday s New England Journal of Medicine that the FDA requested Pfizer halt its phase III study of the drug to treat osteoarthritis after 16 patients knee problems worsened, leading to joint replacement surgery. The drug inhibits the production of nerve growth factor, which stimulates nerve development, triggers pain and is often present in inflamed tissues, such as arthritic joints. Researchers believe that the pain relief conferred by tanezumab was so substantial that patients increased their physical activity enough to accelerate joint damage, ultimately causing them to need joint replacement. The FDA has also asked the company to halt tests of the drug to treat chronic low back and diabetic nerve pain; studies are continuing testing on the drug s efficacy in patients suffering from cancer pain and chronic pancreatitits.
It s unfortunate that the FDA suggested Pfizer suspend the trial since its important to note that these patients would have eventually needed joint replacement, anyway, ACSH's Dr. Elizabeth Whelan points out. This is a novel, non-addictive pain reliever with fewer side-effects that could improve the well-being of cancer patients who do not respond well to the readily available pain relievers on the market.
This is potentially an excellent drug for pain relief but has no impact on stopping or reversing joint erosion, says ACSH's Dr. Gilbert Ross. Since the drug trial for osteoarthritis has been stopped, it s unlikely to get FDA approval for that indication. Therefore, I worry that if the drug is subsequently approved for cancer pain relief, doctors will be able to prescribe it as a pain reliever for osteoarthritis, but only off-label so patients will have to buy it without insurance coverage.