Amgen has suffered a setback with the news that regulators in the USA have delayed a decision on its investigational osteoporosis treatment Prolia.

The US Food and Drug Administration has issued a complete response letter to the company for the Biologic License Applications for Prolia (denosumab) in the treatment and prevention of postmenopausal osteoporosis and “requested several items”. These include further information on the design of Amgen's previously submitted post-marketing surveillance programme and a request for a new clinical plan to support approval of Prolia in the postmenopausal osteoporosis indication.

The FDA stated that a risk evaluation and mitigation strategy is necessary for the drug (the firm has already provided relevant materials) and has also asked for all updated safety data related to denosumab. Amgen’s head of R&D, Roger Perlmutter, says that “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” and the company noted that the letter does not require additional pre-marketing clinical trials to complete the review of the treatment indication.

Amgen added that it expects to receive a separate response for its application for Prolia in the treatment and prevention of bone loss due to hormone ablation in breast and prostate cancer patients.

Analysts do not seem to be overly concerned about the delay. Geoffrey Meacham at JPMorgan issued a research note saying that Amgen can submit its complete response to the agency “fairly quickly given the nature of the FDA requests”. He added that “we would not be surprised if it were done in weeks or less.”

Eric Schmidt at Cowen & Co said that denosumab is still likely to be approved by mid-2010 and believes that sales next year could reach $200 million. However other analyst estimates believe that $400-$500 million is a realistic target.