Amylin falls as Byetta and Exenatide concerns grow

Byetta is Amylin's top-selling drug, and a long-acting version of the drug called Exenatide LAR is set to reach the market ahead of several rival candidates. But trial results in recent days have analysts suggesting that competition may be more difficult than they expected.

Cowen and Co. analyst Phil Nadeau said Exenatide, Novo Nordisk's liraglutide and Roche's R1583 are all "viable" drug candidates, so competition in the class will increase as the other drugs reach the market. Amylin also posted trial results for Byetta and Exenatide over the weekend, and Nadeau said the drugs performed as expected.

The study results were presented at a conference of the American Diabetes Association in San Francisco.

Jim Birchenough of Friedman Billings Ramsey wrote that "real world" data showed Byetta is not quite as effective as it appeared in clinical trials. He said the data suggests the drug's weight loss and blood sugar control benefits fade over time.

Amylin shares fell $3.09, or 10 percent, to $26.84. The stock lost 8.7 percent Friday after Novo Nordisk reported trial data showing liraglutide was more effective than Byetta at controlling blood sugar levels. The stock is down about 18 percent since Thursday's close.

Jefferies analyst Salveen Kochnover said Roche's candidate R1583 could be a threat to sales of Exenatide LAR, as trials show the drugs are about equally effective in reducing blood sugar levels and in weight loss. Both are also dosed once per week, while liraglutide is given once per day.

She added that liraglutide may also pose stiffer-than-expected competition to Byetta. As a result, Kochnover downgraded the stock to "Hold" from "Buy" and cut her price target to $33 per share from $47.

In a telephone interview, Amylin President and Chief Executive Daniel Bradbury said Exenatide LAR is expected to be the first weekly treatment for type 2 diabetes. He added that because it is "aggressive" and does not cause weight gain and severe hypoglycemia, Exenatide "is where (diabetes) therapy is going."