Shares of Amylin Pharmaceuticals Inc. fell Friday after an analyst suggested Amylin's diabetes drug Byetta is more likely to cause pancreatitis than a rival treatment, Merck & Co.'s Januvia.
In a client note published late Thursday, Yaron Werber of Citi Investment Research said Byetta causes about four times as many cases of pancreatitis as Januvia. If there is a link between Byetta and pancreatic inflammation, he said, Amylin may have a harder time getting its extended-release version of the drug approved, and sales could be harmed as well.
In afternoon trading, the stock lost 72 cents, or 3.4 percent, to $20.76.
Werber based his analysis on adverse events reported to the Food and Drug Administration, divided by total prescriptions of each drug and adjusted where possible for total use. Out of every 100,000 patients who took Byetta, he said about 6.49 developed acute pancreatitis. That compared to 1.61 out of 100,000 for Januvia.
He added that Byetta has also been associated with a few cases of pancreatitis that were associated with tissue death, bleeding, or death, while Januvia has not.
The data was collected between Byetta's launch in 2005 and the first quarter of 2008.
"The difference between these two recently launched drugs is striking," Werber said.
In May, he added, two Food and Drug Administration reviewers wrote a letter to the New England Journal of Medicine in which they said Byetta may cause acute pancreatitis because it is derived from Gila monster venom — and exposure to that venom can cause pancreatitis.
Amylin did not immediately return calls seeking comment.
Also known as exenatide, Byetta is a synthetic version of a protein present in Gila monster saliva, and is designed to help diabetics keep their blood sugar under control by imitating a hormone that controls the production of insulin. Its sales reached $177.5 million in the second quarter.
Amylin markets the drug with Eli Lilly & Co. With Lilly and Alkermes Inc., the company is also developing a long-acting version of the drug designed to be injected once a week. The LAR product is in late stage clinical testing, and Werber thinks it will reach the market in mid 2010.