THURSDAY, Feb. 12 (HealthDay News) -- The drug ustekinumab shows promise against psoriatic arthritis (PA), according to a study that included patients from 24 sites in Europe and North America.

PA affects about 11 percent of patients with psoriasis, an autoimmune disease that affects the skin and joints. Some patients don't respond to current drug treatments for PA, so researchers are trying to find alternative therapies, according to background information in a news release about the study.

It's believed that interleukins 12 and 23 may play a role in PA. Interleukins are immune system-produced proteins that mediate inflammatory reactions in diseases such as psoriasis. Ustekinumab prevents interleukins 12 and 23 from binding to cell membranes.

In this study, patients were randomly assigned to receive either: ustekinumab (90 milligrams or 63 milligrams) every week for four weeks, followed by placebo at weeks 12 and 16 (76 patients -- Group 1); or placebo (weeks 0-3) and ustekinumab (63 milligrams) at weeks 12 and 16 (70 patients -- Group 2).

At week 12 of the trial, 42 percent of patients in Group 1 showed improvement, compared with 14 percent of those in Group 2. Of the 124 patients with psoriasis affecting 3 percent or more body surface area, 33 of 63 (52 percent) in Group 1 and three of 55 (5 percent) in Group 2 had a 75 percent or greater improvement in psoriasis area and severity index score at week 12 of the study.

"Our findings show that ustekinumab is efficacious and safe for treatment of active psoriatic arthritis. Our study is one of the first to implicate the role of interleukin 12/23 P40 cytokines in the pathophysiology of this disorder. Larger and longer term studies are needed to further characterize ustekinumab efficacy and safety for treatment of psoriatic arthritis," wrote Dr. Alice Gottlieb, of the dermatology department at Tufts Medical Center in Boston, and colleagues.

The study was published online and was expected to be in an upcoming print issue of The Lancet.

"The efficacy of ustekinumab for improving skin and joint involvement, which was maintained for several months, combined with good tolerability and a benign safety profile, make this agent an attractive option in psoriatic arthritis," Dr. Raquel S. Cuchacovich and Dr. Luis R. Espinoza, of LSU Health Sciences Center in New Orleans, wrote in an accompanying editorial.

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