LOS ANGELES — Dr. Peter C. Butler initially declined a request by the drug maker Merck to test whether its new diabetes drug, Januvia, could help stave off the disease in rats.
“I said, I’m not interested in your money, go away,” Dr. Butler recalled.
Merck no doubt now wishes it had. When Dr. Butler finally agreed to do the study, he found worrisome changes in the pancreases of the rats that could lead to pancreatic cancer. The discovery, in early 2008, turned Dr. Butler into a crusader whose follow-up studies now threaten the future of not only Januvia but all the drugs in its class, which have sales of more than $9 billion annually and are used by hundreds of thousands of people with Type 2 diabetes.
“I knew some stuff that I thought was a worry and I was obliged to pursue it,” said Dr. Butler, the chairman of endocrinology at the University of California, Los Angeles.
Based on his latest study, both the Food and Drug Administration and the European Medicines Agency have begun investigations that could lead to new warnings on the drugs, or even to their removal from the market.
Or they could result in no action at all.
Dr. Butler faces powerful opponents in the makers of the drugs and many diabetes specialists, who say his studies are contradicted by other evidence.
“The data are inconclusive,” said Dr. Robert Ratner, chief scientific and medical officer of the American Diabetes Association. He said even if there were some excess risk, it would be “exceptionally low.”
Nancy Thornberry, who heads diabetes drug development at Merck, said that clinical trials, the gold standard of medical evidence, had found no increased risk of pancreatic disease from Januvia, even when results of trials were pooled to achieve greater numbers. “In fact, my mother takes sitagliptin,” she added, referring to Januvia by its generic name.
Questions about whether the drugs raise the risk of pancreatitis, a painful and possibly lethal inflammation of the pancreas, arose soon after the first one, Byetta, now sold by Bristol-Myers Squibb and AstraZeneca, was approved in 2005. The drugs’ labels already contain warnings about that. What is new and potentially more serious is a possible risk of pancreatic cancer, which is virtually untreatable and kills most victims within a year.
Many people in the field compare Dr. Butler to Dr. Steven Nissen, the well-known Cleveland Clinic cardiologist whose warnings about Avandia, a different type of diabetes drug, led to its being banned in Europe and highly restricted in the United States.
Both men have faced criticism from those who call them zealots. The F.D.A. is about to examine data suggesting that Avandia might not be so dangerous after all. Some critics say Dr. Butler overstates his conclusions and that his findings have not been replicated by others.
“Basically, no one in the entire world over the last 10 years, with thousands of animals,” has found what Dr. Butler found, said Dr. Daniel J. Drucker, a professor of medicine at the University of Toronto and a consultant to many drug companies.
Still, Dr. Butler is not easy to write off. He is a former editor of Diabetes, the flagship journal of the American Diabetes Association. And he has some defenders.
“He should be an American hero, actually, a rugged individualist who is not going to be browbeaten,” said Dr. Edwin Gale, professor emeritus at the University of Bristol in Britain, who recently wrote a commentary with Dr. Butler on the drugs.
Dr. Butler was born in Kenya to British parents, though he has worked in the United States since 1987 and is an American citizen. His wife, Dr. Alexandra E. Butler, a pathologist who occupies the office next to his, has also worked on some of the studies.
In the last month, lawyers defending drug companies against a lawsuit claiming that Byetta had caused a patient’s pancreatitis, subpoenaed virtually all of Dr. Butler’s records.
“I think the message here is they want him out of business,” said Brian Depew, a lawyer representing the plaintiff, Ross Hubert of New Hampshire, who claims that Byetta caused him to get pancreatitis. Dr. Butler said U.C.L.A. told him not to comment on the subpoena.
More than 100 lawsuits representing 575 plaintiffs around the country are claiming injury from Byetta, mostly pancreatitis, according to the latest quarterly regulatory filing from Bristol-Myers. Forty-three suits claim that Januvia caused pancreatic cancer, according to Merck.