Centocor Inc., a unit of Johnson & Johnson, announced yesterday that federal health regulators asked for further information about its experimental drug designed to treat psoriasis.

Centocor has asked the Food and Drug Administration to approve ustekinumab, a drug created to treat the immune system disorder. In a letter addressed to the biotechnology company, the agency demanded Centocor to develop a plan for notifying doctors and patients about potential risks.

Ustekinumab’s manufacturers expect to respond to the federal regulators at the beginning of the next year. Until then, they keep on focusing on bringing the drug to market, said Jerome Boscia, a clinical-research and development executive at the company.

In June 2008, several outside experts recommended the FDA to approve the psoriasis drug. However, they also voiced concern about the drug’s potential to boost the risk of developing cancer and added that long-term information is needed.

Psoriasis is a non-contagious disorder that affects both the skin and joints. Its cause is still unclear, but researchers believe it is something genetic. However, some factors are known to worsen the chronic recurrent condition, stress, smoking and excessive alcohol intake counting among them. The disease affects over 17 million people in the United States and Europe.

According to Cowen & Co. analyst Sara Michelmor, Ustekinumab peak sales could reach more than $500 million.