Other arthritis drugs on the market either treat just the symptoms, or employ a broader, more scattershot effect against the underlying process. Such drugs can have toxic side effects because they kill healthy cells along with the diseased ones.
The latest research, an international study led at University College London and published in Thursday's New England Journal of Medicine, looked at a drug called rituximab, and the results were promising.
"I think this is a pivotal study," said Dr. John Klippel, president of the Arthritis Foundation. "This is opening up a new era of targeted biologic therapies for rheumatoid arthritis."
In rheumatoid arthritis, antibodies misdirect friendly fire against the body's own joint linings. Joints become inflamed, swollen and painful. More than 2 million Americans, mostly women, have the disease.
Rituximab, which is sold under the brand name Rituxan and is already approved for non-Hodgkin's lymphoma, targets B cells, which manufacture these antibodies.
The researchers compared rituximab to other drugs in 161 patients with arthritis.
For two weeks, patients took rituximab alone or in combination with two other drugs: the standard drug, methotrexate, and the less widely used cyclophosphamide. Another group took methotrexate alone. Roche, a distributor of rituximab, funded and participated in the study.
After six months, more than 40 percent of patients who took rituximab combinations were greatly improved. One-third of patients on rituximab alone were greatly improved. But only 13 percent of those on the standard drug alone improved that much.
"One of the things that is truly unique is that a very short course ... appears to have a very long-lasting effect," Klippel said.
Some doctors, including the study's authors, said rituximab needs more testing before any widespread use. They said other B-cell-killing drugs are under development and could eventually outperform rituximab.
Researchers are also testing similar targeted approaches against lupus, multiple sclerosis and other autoimmune diseases.
Both methotrexate and cyclophosphamide are sometimes employed as chemotherapy drugs and attack a broader range of tissue than rituximab. The newer drug kills close to 90 percent of B cells, which the body then replenishes with healthy new ones.
Rituximab is one of the most narrowly aimed and efficient members in the modern family of targeted drugs that include the breast cancer treatment Herceptin.
Of all the tested treatments for rheumatoid arthritis, "it goes closest to the root of the disease," said the study's lead author, Dr. Jonathan Edwards of University College London.
However, the drug could pose a danger of chest infection, especially if given repeatedly, Edwards said. One rituximab patient in the study died of pneumonia, though it was not clear if the drug was responsible.
By Jeff Donn