Amgen suffered a setback Oct. 19 as federal regulators withheld approval of a new drug that investors hope will be the Thousand Oaks company’s next blockbuster.

The Food and Drug Administration held up approval for denosumab, a treatment for bone loss in older women. Federal regulators want more information on how Amgen will monitor the drug’s safety after it hits the market, Amgen said in a release.

Investors did not seem panicked at the news. Shares were down about 1 percent by midday.

Amgen is counting on the new drug because its biggest selling kidney and anemia treatments have lost sales over safety and dosing concerns in the past two years.

The FDA didn’t ask for more clinical trials for the new drug, Amgen said in the release. Trials are typically the most costly and time consuming part of getting a drug approved.

Still, analysts quoted by Bloomberg News said the Oct. 19 response from the FDA could push the approval of denosumab into next year. Joshua Schimmer of Leerink Swann told investors in a note that the FDA’s move could set back approval 10 months, while Geoff Meacham, a JPMorgan Chase & Co. said in a note that Amgen could have its initial response together in a matter of weeks.

Amgen officials sought to defray investor alarm that the FDA’s request could hurt future sales of denosumab.
“We are confident that we can quickly respond to the FDA’s requests for the treatment of postmenopausal osteoporosis indication and plan to do so in the near term,” Roger Perlmutter, Amgen’s head of research and development, said in a release.

Amgen is seeking approval for denosumab for two uses, the treatment and prevention of osteoporosis in older women.

The FDA’s Oct. 19 request affects the application for the use of the drug as a treatment. Amgen suffered a another set back this summer with its application to use the drug for osteoporosis prevention when some breast cancer patients had hormone problems after using the drug.

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