A panel of outside experts to the U.S. Food and Drug Administration voted 8-2 to recommend approval of tofacitinib, a treatment for patients with rheumatoid arthritis who have not had success with at least one other drug for the disease.

Analysts see tofacitinib as a potential blockbuster, with peak sales of $2 billion to $3 billion a year, if its benefits are deemed to outweigh the risks. It could also help revive faith in Pfizer's research prowess. The company has not produced a major new medicine from its own labs since impotence treatment Viagra more than a decade ago.

Pfizer shares, which rose as much as 2.6 percent after the vote, closed 1.1 percent higher at $22.45.

The FDA usually follows panel recommendations, although it is not required to do so, and a final decision is expected in August.

If approved, the likely cheaper pill would compete with widely used injectable medicines, including Abbott Laboratories Inc's $8 billion-a-year biologic drug, Humira.

"I think the data for efficacy is compelling and it's at least as good as other biologic agents," said Dr. Maria Suarez-Almazor, panel member and section chief in rheumatology at MD Anderson Cancer Center in Houston.

However, most panelists said the drug should only be used once patients had tried at least several other drugs for the disease, not just one. They expressed concern about some of its side effects, such as infections and malignancies, or cancerous cells that can spread.

"There are enough safety signals that are concerning ... so I wouldn't be comfortable starting one of my patients right after one (rheumatoid drug) failure," Dr. Suarez-Almazor said.

In a review earlier this week, FDA staff said tofacitinib may have a higher risk of serious infections such as pneumonia and a possible link to malignancies, which may get worse with higher doses or longer exposure to the drug. Panelists called on Pfizer to study the drug's safety post-approval.

Most analysts said the panel's vote meant the drug was likely to be approved, although doctors were unlikely to prescribe it to patients unless they had tried several other options, limiting initial sales.

LUCRATIVE FIELD

Rheumatoid arthritis and related diseases have been one of the most lucrative areas for drugmakers, with more than $20 billion in annual sales.

An estimated 1.3 million Americans suffer from rheumatoid arthritis, according to the Arthritis Foundation. About 1 percent of the world's adult population has the disease.

Besides Humira, other treatments include Enbrel, made by Amgen Inc, and Johnson & Johnson's Remicade. All of these are costly, injectable drugs that block a protein called tumor necrosis factor (TNF) that is tied to inflammation.

Pfizer's treatment is a traditional chemical pill that works by blocking signals that activate immune and inflammatory responses in the body. It is the first in a new class of drugs called JAK inhibitors.

Analysts and doctors have said about 30 percent to 40 percent of patients with rheumatoid arthritis do not respond to available drugs, meaning there is room for other options.

Tofacitinib's most attractive feature over older drugs may be its dosing. Patients take it twice a day in tablet form, rather than having to inject themselves every other week, as with Abbott's Humira.

Pfizer is also studying the drug for other conditions, including inflammatory bowel diseases, psoriasis and dry eye.

"The (rheumatoid arthritis) patient population needs additional treatment options and Pfizer looks forward to working with the FDA on next steps," Dr. Yvonne Greenstreet, senior vice president and the head of Medicines Development Group for Pfizer Specialty Care, said in a statement.

(Editing by Maureen Bavdek, Matthew Lewis and Andre Grenon)

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