Johnson & Johnson said on Friday U.S. regulators approved its new treatment for psoriasis, called Stelara, for patients 18 years or older with moderate to severe psoriasis.

Stelara, deemed a potential blockbuster because of its effectiveness and infrequent administration, has been awaiting approval since late 2007. The U.S. Food and Drug Administration had extended its review of the product on several occasions to study amendments to J&J's marketing application and to review other information.

Stelara's main advantage is its more-convenient dosing, said Wells Fargo analyst Larry Biegelsen. He noted that it is given by injection only once every three months, compared with injections every few weeks with the leading class of drugs called tumor necrosis inhibitors -- including Abbott Laboratories Inc's Humira.

The J&J drug will likely generate sales of $130 million in 2010, growing to more than $500 million in 2013, Biegelsen said.

Psoriasis, in which itchy red plaques accumulate on the surface of the skin, is caused by an overproduction of skin cells. It affects an estimated 7.5 million patients in the United States.

Stelara, whose chemical name is ustekinumab, is a monoclonal antibody that proved superior to Amgen Inc's and Wyeth's injectable Enbrel in one study. It works by taming two immune system proteins called interleukin-12 (IL-12) and interleukin-23 (IL-23) that are linked to inflammation.

It was well tolerated in large studies, with generally mild side effects that did not require adjustments in the medicine. But J&J cautioned on Friday that some serious infections have been linked to the drug and that it may increase the risk of cancer.

Current treatments -- including Enbrel, Humira and J&J's older Remicade medicine that is given by intravenous infusion -- can also increase risk of infection.

(Reporting by Ransdell Pierson; editing by Andre Grenon and Carol Bishopric)