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Common Pain Reliever May Not Treat Knee Pain

Acetaminophen No Better Than Sugar Pills in Treating Knee Pain Caused by Osteoarthritis
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WebMD Health News

Aug. 11, 2004 -- Pain relievers containing acetaminophen are widely recommended for the treatment of knee pain caused by osteoarthritis, but new research suggests that acetaminophen may be no more effective than sugar pills.

The findings call into question recommendations by a number of large arthritis groups endorsing acetaminophen as a primary treatment for osteoarthritis. Acetaminophen is the active ingredient in Tylenol and many other over-the-counter and prescription drugs.

A spokesman for one of those groups, the American College of Rheumatology, says there have been few clinical trials comparing acetaminophen to placebo for the relief of arthritis-related pain.

"This is the second study that I know of to show no benefit beyond placebo, but the literature has been mixed, at best," Steven Abramson, MD, tells WebMD. "It is clear, however, that this treatment does not work in the majority of patients, and we can't assume that it is safe for use long-term at the high doses used in this trial."

Placebo Effect

In the new study, slightly more than half of the 405 osteoarthritis patients treated for six weeks with 4 grams a day of acetaminophen -- the equivalent of eight Extra Strength Tylenol -- reported significant reductions in pain. But an almost identical percentage of patients unknowingly taking the dummy pills reported the same thing, an effect know as the placebo effect. The findings are published in the latest issue of the Annals of Rheumatic Diseases.

The placebo effect seen in the study was seen in many more people than usually reported in studies of pain relievers.

"It would be hard for any active medication to show effectiveness against a placebo when the placebo effect is so large," says Abramson, who is director of rheumatology at the NYU Hospital for Joint Diseases. "This may be just the researchers' bad luck, or it may suggest an unusually high placebo effect among patients with osteoarthritis."

Osteoarthritis is the most common type of arthritis. It causes destruction of cartilage, inflammation of joints, and pain.

The active treatment did appear to be more effective than placebo in a subgroup of knee pain patients without evidence of inflammation. And the 4 gram dosage was well tolerated during the six-week study.

But the study says little about the long-term safety of this dosage of acetaminophen, says Arthritis Foundation spokesman Hayes Wilson, MD. Wilson cited findings from a large, ongoing study of nurses, reported late last month, suggesting that long-term acetaminophen use can cause kidney damage.

"We think of [acetaminophen] as a really benign drug because it doesn't cause ulcers and is well tolerated," says Wilson, who is chief of rheumatology at Piedmont Hospital in Atlanta. "But there is a suggestion that it may not be as safe as we think."

'Starting Point'

Abramson and Wilson agreed that in the absence of definitive data showing acetaminophen to be a poor choice for the treatment of osteoarthritis of the knee, physicians will continue to use it as a primary treatment. Patients who do not respond are generally switched to other pain relievers.

"Acetaminophen is a good starting point," Wilson says. "It is inexpensive and well tolerated, but most patients end up moving on to something else."

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