An experimental rheumatoid arthritis pill discovered and developed at Pfizer Inc. research sites in Groton and New London won praise Wednesday at a meeting of scientists in London, despite news that up to two deaths in a key study could be linked to the drug.

Pfizer previously had said only one of the four people who died during a late-stage trial of tofacitinib had succumbed because of complications related to the drug's effects. But Reuters news service reported that Joel M. Kremer of Albany Medical College, the study's primary investigator, said during an interview at the European League Against Rheumatism meeting that it's possible the respiratory failure of a 48-year-old Russian was linked to tofacitinib.

"It's unlikely that two of the four (deaths) were associated (with tofacitinib," Reuters quoted Kremer as saying. "It's possible that the other two of the four were associated, but based upon the information I have it's impossible to say with absolute certainty."

Pfizer gave detailed results of its so-called ORAL Sync trials of tofacitinib at a news conference.

Among the findings were that more than half of patients on a higher dose of tofacitinib reported 20 percent improvements in such common rheumatoid arthritis symptoms as swollen joints and pain. Patients started seeing relief within two weeks.

Scientists in London reportedly gave a thumbs up to the results, though some expressed concerns about the drug's safety profile.

"It's clear that you have to be careful about a drop in white blood cell counts, which is usually mild but can lead to increased rates of infection," Georg Schett, head of rheumatology and immunology at the University of Erlangen-Nuremberg, told Reuters.

But scientists said the number of deaths reported in the study was no more than would have been expected in the rheumatoid-athritis population as a whole. The 792 patients in the study all had failed to respond to existing biotech drugs, such as Abbott Laboratories' blockbuster Humira.

Pfizer is hoping that tofacitinib will be the first blockbuster out of its labs since Viagra - discovered by company scientists at the Sandwich, England, site that soon will be shuttered - hit the market more than a decade ago. Humira currently has a worldwide market of $6.5 billion, and current projections for tofacitinib place its potential at more than $1 billion in sales within four years.

Pfizer, which has not yet filed for regulatory approval to use tofacitinib in treating patients with rheumatoid arthritis, is also studying the drug in psoriasis, inflammatory bowel disease, kidney transplant and eye disease.

"Pfizer is encouraged by the efficacy and safety findings," said Yvonne Greenstreet, the company's leader for the Medicines Development Group.

l.howard@theday.com