By Ransdell Pierson
(Reuters) - A high dose of Pfizer Inc's drug, tofacitinib, proved as effective as the widely used treatment Enbrel in treating adults with moderate-to-severe psoriasis in a late-stage study, while a lower dose of tofacitinib was less effective than Enbrel, the drugmaker said on Wednesday.
Analysts said the mixed results, from a 12-week study called OPT Compare, suggest there would be limited demand for tofacitinib as a treatment for psoriasis if it is eventually approved for the inflammatory skin condition affecting more than 7 million Americans.
The study examined the effectiveness of both 5 milligram and 10 milligram twice-daily doses of oral tofacitinib with a placebo and with the approved twice-weekly starting dose of injectable Enbrel.
Pfizer said tofacitinib, already approved to treat rheumatoid arthritis under the brand name Xeljanz, showed similar dose-response trends and similar safety trends as those seen in an earlier mid-stage trial of tofacitinib for treatment of psoriasis.
ISI Group analyst Mark Schoenebaum said the findings suggest that tofacitinib, at the 10 milligram dose, has "biologic-like efficacy," meaning effectiveness on par with costly biotech drugs like Enbrel that are grown in living cells.
But Schoenebaum noted that although tofacitinib had been studied at both the 5 milligram and 10 milligram doses for rheumatoid arthritis, it was only approved for the 5 milligram dose due to concerns of increased safety risk of the higher dose.
"As a result, there is a risk that only the 5 milligram dose is approved in psoriasis and dermatologists will view (tofacitinib) to be inferior to Enbrel and other biologics with a similar and less robust pool of long-term safety data," Schoenebaum said.
Citi analyst Yaron Werber said mid-stage trials of tofacitinib showed serious side effects at all dosages, including cardiovascular events, elevated cholesterol and decreases in hemoglobin.
"Based on our doctor checks, the safety of tofacitinib is not clean enough to garner broad use by the risk-averse dermatology community," Werber said in a research report.
Xeljanz, approved last November for rheumatoid arthritis, had second quarter sales of $22 million. But some industry analysts expect it to eventually capture annual sales of $1 billion or more, as an alternative to injectable biotech arthritis drugs like Enbrel and Abbott Laboratories Inc's Humira that have their own side effect issues.
On Wednesday, Pfizer said tofacitinib met its primary effectiveness goal in a separate Phase III psoriasis study, called OPT Retreatment, which lasted 56 weeks and compared the 5 milligram and 10 milligram doses of tofacitinib to a placebo.
That study compared the effectiveness and safety of withdrawal and retreatment with both tofacitinib doses, compared with placebo, in adult patients with moderate to severe psoriasis.
A greater proportion of patients taking tofacitinib maintained symptom relief during the withdrawal of treatment compared with patients who switched to placebo, Pfizer said in a statement.
Pfizer said full data from the pair of Phase III studies, the first of five late-stage trials of tofacitinib for psoriasis, will be presented at a future scientific meeting. Data from two more of the large studies is expected in the second quarter of 2014, Pfizer said.
Shares of Pfizer slipped 0.3 percent in midday trading on the New York Stock Exchange.
Psoriasis is a chronic inflammatory disease of the skin, which also affects nails, joints and other organs. An estimated 125 million people worldwide have the condition, according to Pfizer, including 7.5 million in the United States.
The disease is caused partly by an overactive immune system, which causes the body to grow skin cells up to 10-fold faster than normal. The cells build up on top of each other to form raised red patches of plaque on the skin.
Enbrel, a blockbuster product sold by Amgen Inc and Pfizer, works by blocking a protein called tumor necrosis factor, that is linked to inflammation.
Tofacitinib is a so-called JAK inhibitor, as it blocks an enzyme called Janus kinase that is also associated with inflammation.
(Editing by Bernadette Baum and Bob Burgdorfer)