'Game-Changing' Arthritis Drug Blocks Pain Too Well in Some

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The effect persisted through four months of treatment, allowing some patients to do previously unheard-of things like dance again, Lane said. The medication also reduced stiffness and improved physical function more than the placebo, with only mild to moderate side effects, which generally dissipated in a few days. The most common were headache, upper respiratory infection and pricking or tingling sensations in the hands and feet.

But tanezumab's potential as an arthritis pain reliever has been tempered by emerging evidence that use can lead to joint failure, said John N. Wood of the Wolfson Institute for Biomedical Research at University College, London, in an accompanying editorial in the New England Journal. Since the UC Davis-led study ended on May 24, 16 patients in a Phase III study of the drug in knee and hip osteoarthritis suffered joint breakdown that required total joint replacements.

At the FDA's request, Pfizer in June suspended studies of the drug for osteoarthritis. In July, it also suspended tanezumab studies for lower back pain and diabetic nerve damage, but said it would continue investigating its potential for other conditions, including cancer pain.

In an interview Wednesday, Lane called the tanezumab "a game-changing medication. We've never had an agent this potent. You get something that takes the pain away, you're bound to accelerate the disease."

She described researchers as so dazzled by tanezumab's powerful analgesic effect that they didn't warn their patients to take it easy.

"We've never had anything like this. We didn't know to counsel our patients, to say, 'This is like Novocain that the dentist gives. You're not going to feel anything...

"' Everyone got so excited by the findings, they didn't realize that everyone who has pain -- they aren't necessarily going to sit in a chair all day."

Experimental Drug May Have Advantages Over Current Treatment

Of those patients, she said: "We didn't monitor activity ... or how hard they were pushing, loading their joints. We just let them go to town. And they did."

Lane said the drug has multiple advantages over current analgesics: "It's not a narcotic, so it doesn't mess with your brain and intestines. It doesn't hurt your stomach. It has no effect at all on the kidneys and liver." With so many factors in its favor, she said it's up to the medical research community "to figure out how to use it so patients can benefit. We want to maximize the benefit and lower the risk."

Lane said she was grateful that the destructive side effects appeared while the drug was still experimental, rather than "when the drug was out. Now we can counsel patients, rather than have the drug withdrawn like the COX-2 inhibitors," which were taken off the market when they caused heart problems. "I think this is responsible drug development. Thank goodness it happened now."

While studies of the drug remain suspended at the request of the FDA, she said, "there are there other companies that have this type of a medication in development right now." Those companies have told her the FDA advised them to "go ahead cautiously. I think we will see a nerve growth factor inhibitor on the market -- whether it will be Pfizer's, I can't say."

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