NEW YORK (Reuters) - Pfizer Inc's experimental pill for rheumatoid arthritis appeared to be effective and well-tolerated in a mid-stage clinical study, the drugmaker said.
The drug, known as CP-690,550, achieved the main goal of 20 percent improvement (ACR 20) of symptoms after 12 weeks in patients suffering from the painful joint-swelling condition at all but one of the tested doses.
Significantly more patients reached the ACR 20 goal on the medicine than did those who received a placebo.
Data from the interim analysis of the 509-patient, 6-month study were to be presented next week at the American College of Rheumatology meeting in San Francisco.
Rheumatoid arthritis is an auto-immune disease, whose cause is unknown, but leads to pain, swelling and loss of function in joints. It affects 2.1 million Americans, according to the Arthritis Foundation.
Although several years away from potentially reaching the market, CP-690,550 is part of a new class of rheumatoid arthritis therapies that could be more convenient for patients who must take most current medicines by injection or infusion.
The medicine's development also is being closely watched by stock analysts and investors, who are concerned that Pfizer lacks sufficient drugs in its experimental pipeline to make up for expected revenue declines when its Lipitor cholesterol medicine loses U.S. patent protection in 2011.
CP-690,550 arguably is Pfizer's most important mid-stage product, JP Morgan analyst Chris Schott said in a research note last month.
The Phase 2b study involved patients with moderate to severe rheumatoid arthritis who failed to respond completely to methotrexate, an older medicine.
The study had six arms for patients on various doses of CP-690,550 taken either once or twice a day, and one arm with patients on a placebo. All patients in the study continued to take methotrexate.
At doses of 3 milligrams, 5 mg, 10 mg and 15 mg twice a day, and 20 mg once a day about 60 percent of patients achieved at least the ACR 20 goal compared with 38 percent in the placebo group.
The 1 mg dose failed to reach statistical significance compared to a placebo.
Researchers noted an onset of efficacy at as early as two weeks into treatment with the Pfizer drug. Efficacy peaked at eight weeks and was maintained at 12 weeks, Pfizer said.
The most commonly reported adverse side effects in those taking the drug were nausea, headache and increased liver enzymes. Analysts have said that the liver enzyme issue could prove to be a stumbling block on the way to approval.
Incidence of adverse side effects were higher at higher doses, the company said.
Only five patients in the study suffered serious infection, which is a fairly common side effect of anti-inflammatory
biotechnology medicines for rheumatoid arthritis.
CP-690,550 is part of a new class of drugs known as JAK3 inhibitors that work by blocking the JAK3 enzyme, which activates white blood cells critical to the immune system.
Pfizer plans next year to start a larger Phase 3 study -- the last stage of human testing before the drug can be submitted to regulators for approval.
"The idea of a medicine that's a simple tablet, just a pill that you can take once or twice a day compared to an infusion or injection, will be very, very appealing to many doctors and patients," said Gail Cawkwell, an executive medical director at Pfizer. "But our Phase 3 studies are really needed to compare to other existing treatments and to get a sense of how the drug performs in the long term."
Additional reporting by Bill Berkrot; editing by Carol Bishopric