National Editor

Bolstered by positive data from three Phase III studies, Amgen Inc. filed a new drug application for cinacalcet hydrochloride, its calcimimetic licensed from NPS Pharmaceuticals Inc. in 1996 for secondary hyperparathyroidism (also known as SHPT) associated with chronic kidney disease.

"There's nothing else out there [with cinacalcet's mechanism of action]," said Kelly Stoddard, spokeswoman for Thousand Oaks, Calif.-based Amgen. "That's the important thing for people to understand."

Analysts expected the filing, and Amgen's stock (NASDAQ:AMGN) closed Monday at $67.42, down 78 cents.

The orally active treatment is Amgen's first small-molecule therapeutic. Cinacalcet modulates the calcium-sensing receptor on the parathyroid gland.

By increasing sensitivity of the receptors to calcium levels in the bloodstream, cinacalcet is believed to reduce parathyroid hormone levels, along with calcium and phosphorous - all of which often add up to a serious problem for patients with end-stage renal disease who are undergoing dialysis.

The symptoms are bone loss, bone pain, soft-tissue calcification and severe itching. High-dose vitamin D is deployed in an attempt to lower parathyroid hormone. An estimated 85 percent of the 300,000 ESRD dialysis patients in the U.S. are afflicted.

For NPS, which is in line for royalties if cinacalcet is approved, the filing means a $6 million milestone payment.

William Tanner, analyst with Leerink Swann & Co. in Boston, estimated the revenue opportunity at about $250 million in 2005, based on a survey done by MEDACorp, a division of Leerink.

Polled were 30 physicians who had treated a total of about 7,000 patients with ESRD in 2002, Tanner wrote in a research note. About 35 percent of the patients were given oral vitamin D (calcitriol) therapy. Of those, about 70 percent said their condition was well controlled with vitamin D - but if cinacalcet, a superior therapy, were priced within an acceptable range, it could still take market share, Tanner noted.

"Obviously we believe in the product or we wouldn't have filed" the NDA, Stoddard said. Treatments options now are "pretty much all vitamin D," she added, pointing out that "this is a new area of chronic kidney disease [for Amgen]."

Asked about market share, Stoddard said it's too early to speculate about how many might benefit from the drug. "I don't think we really have all the numbers," she said.

Data from the Phase III studies with cinacalcet will be presented at the American Society of Nephrology meeting that begins Nov. 12 in San Diego.