WASHINGTON - Eli Lilly and Amylin Pharmaceuticals Inc. on Tuesday reported four new deaths in patients taking Byetta, even as the companies tried to shore up the safety profile of their popular diabetes medication.

The announcement comes a week after the Food and Drug Administration said two Byetta patients died of acute pancreatitis, sinking shares of both drugmakers. An executive from Eli Lilly said the FDA was aware of the additional deaths but did not announce them because they involved a milder form the pancreatitis. The condition can cause nausea, vomiting and abdominal pain.

"They were concentrating on the more severe forms of the condition, but we felt it was important to get this information out there," Eli Lilly Medical Director James Malone told the Associated Press.

Malone stressed that all four patients had complicating medical conditions, ranging from leukemia to gallstones, which were likely the primary cause of death.

Since the FDA announcement, Eli Lilly shares have fallen over 3 percent, while shares of Amylin Pharmaceuticals have fallen nearly 20 percent. San Diego-based Amylin co-developed Byetta and makes about 80 percent of its revenue from the injectable drug. The drug accounted for about 3 percent of Lilly's sales last year.

Prescriptions for the twice-daily treatment fell 2.1 percent last week, according to pharmaceutical data firm IMS Health.

Company representatives scheduled a conference call Tuesday evening to stress how rare the reported problems have been.

In an interview ahead of the call, Malone said that media coverage of the deaths with Byetta "tended to be a bit sensationalized."

He noted there has only been one report of pancreatitis for every 3,000 patients taking the drug for one year.

While the company cannot rule out a connection between its drug and the pancreas problems, Malone said there have been reports of similar problems with rival medications.

"With all other diabetes medications we know there has been pancreatitis and some of those people have died," said Malone. "So it's not a unique phenomenon with Byetta." He added that diabetes patients are already three times more likely to develop pancreatitis compared with healthy patients.

The FDA said last week it would seek a stronger, more prominent warning for Byetta, but details of the new label are still in the works.

Malone also tried to ease concerns about the timeline for company's long-acting version of Byetta _ which is formulated for use once a week, instead of twice a day. He said the companies still hope to bring the drug to market by mid-2009 and that there are no plans for additional studies, despite the FDA's safety concerns.

Lilly and Amylin Pharmaceuticals split worldwide sales of Byetta, which grew over 50 percent to $650 million last year. Wall Street continues to maintain a positive outlook for the drug and the next-generation formula.

Leerink Swann & Co. analyst Jonas V. Alaenas, reaffirmed an "Outperform" rating on Amylin Monday, calling the pancreatitis concerns "overblown." Last week, Goldman Sachs analyst Meg Malloy reaffirmed a "Buy" rating with a similar comment.

Approved in 2005, Byetta was the first in a new class of diabetes medications that have shown improved ability to control blood sugar levels. The drug is expected to face competing products as soon as next year.

In June, Danish drugmaker Novo Nordisk reported data showing its experimental drug liraglutide was more effective than Byetta at controlling blood sugar levels. Swiss firm Roche is also working on its own next-generation diabetes medication.

Considering competition from Novo Nordisk and others, Robert Hazlett expects long-acting Byetta to make $100 million in sales during its first year on the market, compared with earlier analyst estimates of up to $700 million.

Lower revenues from the drug would also impact biotech company Alkermes Inc., which helped develop the longer-acting formula and is slated to receive royalties from its sales.