Pfizer said that its experimental rheumatoid arthritis drug met the main goals of a late-stage clinical trial, a welcome boost for the world's largest drugmaker as it seeks new products to offset those that are losing patent protection.

The drug, tofacitinib, is one of the most important in Pfizer's pipeline. The company said the safety profile of the drug was consistent with that seen previously in the clinical program, and no new safety signals were seen.

The trial showed the drug reduced the signs and symptoms of rheumatoid arthritis by a statistically significant amount compared with a placebo at six months. The drug significantly improved physical function at three months. It also showed significantly greater disease remission at six months.

The trial tested the drug in patients with moderate to severe disease who had failed to respond adequately to traditional therapies.

The trial is the second of six late-stage trials. Results of the first were released last November. Damien Conover, an analyst at Morningstar, expects the drug, if approved, to generate peak annual sales of about $2 billion.

While that would not be enough to offset the expected loss of sales from Pfizer's cholesterol drug Lipitor, which generated nearly $11 billion last year and is set to lose patent protection in November, it would be a start. Investors are reasonably optimistic that the drug will be approved, but Conover said it may take longer than expected since it was shown in a previous trial to raise bad cholesterol and liver enzymes in some patients.

"We're in a climate where the FDA is very risk averse," Conover said, referring to the U.S. Food and Drug Administration. "I think there is a strong likelihood we'll see delays, potentially the need for new trials."

The medicine, previously known as tasocitinib, belongs to a new class of oral drugs, known as JAK inhibitors, that affect the signaling of proteins involved in inflammatory and autoimmune diseases.

If approved, Pfizer's drug would compete with multiple injectable treatments such as Humira, made by Abbott Laboratories, Amgen Inc's Enbrel, and Remicade, made by Johnson & Johnson.

Tim Anderson, an analyst at Sanford Bernstein, said the fact that Pfizer's drug is given by mouth gives it a strong competitive advantage.

"It is an oral therapy that will be competing in a category dominated by injectable products that currently sell about $12 billion a year in rheumatoid arthritis, or about $20 billion when considering other indications," he said in a recent research report.

If the drug proves acceptably safe, Anderson said, he assumes Pfizer will have to price the drug at a discount of about 20 per cent to injectable products, implying a cost of about $17,000 a year, though if all the data are good an argument might be made for equivalent pricing.

Pfizer is one of several companies developing JAK inhibitors, but Pfizer is in the lead.

Shares of Pfizer fell 0.9 per cent to $19.60 in afternoon trading on the New York Stock Exchange. – Reuters