Abbott Laboratories Inc. on Monday said its arthritis drug, Humira (adalimumab), proved effective in treating arthritis associated with the skin disorder psoriasis in a late-stage clinical trial.

Humira is already sold as a treatment for rheumatoid arthritis. Abbott said it would use the new data to seek approval from U.S. and European regulators to treat psoriatic arthritis by the end of this year.

The company has forecast 2005 global Humira sales in excess of $1.2 billion. Approval for the new indication would likely come in late 2005, the company said.

Psoriatic arthritis is an autoimmune disorder that combines symptoms of psoriasis, such as dry, scaly skin, with arthritis symptoms such as joint pain and inflammation.

Amgen Inc. has already received U.S. approval to sell its similar arthritis drug, Enbrel, for psoriatic arthritis.

In the study, which will be presented on Tuesday at the American College of Rheumatology annual meeting in San Antonio, Texas, patients taking Humira showed significant improvement in both joint and skin symptoms, compared with those taking a placebo, researchers said.

The 313 patients in the trial had previously failed to show improvement when treated with non-steroidal anti-inflammatory drugs, such as Motrin or ibuprofen.

The primary goal of the trial was to show a 20 percent improvement in tender and swollen joint count, or ARC20.

At 24 weeks, 39 percent of patients treated with Humira achieved a 50 percent improvement (ACR50) and 23 percent reached ACR70, compared to six percent and one percent in the placebo group.

For psoriasis symptoms, 42 percent of Humira patients experienced at least 90 percent improvement at 24 weeks.

Zero percent achieved 90 percent improvement in the placebo group, researchers said.

One percent of the placebo group reached 75 percent improvement.