CORRECTED-UPDATE 1-FDA staff reviewers flag safety concerns over Cytokinetics' heart drug

(Corrects the drug's spelling in paragraph 3)

Dec 9 (Reuters) - U.S. Food and Drug Administration staff reviewers on Friday identified safety and efficacy concerns about Cytokinetics Inc's heart drug, according to briefing documents published on the agency's website.

The late-stage data raises concerns about the drug's dose-limiting risks of heart failure, the reviewers said, adding it is unclear if the study would be enough to provide evidence of the treatment's effectiveness.

The company's experimental drug, omecamtiv mecarbil, aims to reduce the risk of heart-related death or the need for hospitalization or other urgent care.

A panel of the health regulator's outside experts is scheduled to discuss approval on Dec. 13, and a decision is expected by Feb. 28.

The drug works by activating cardiac myosin, a protein in heart muscle cells responsible for converting chemical energy into the mechanical force that drives cardiac contraction.

Shares of the California-based company fell marginally in early trade on Friday. (Reporting by Bhanvi Satija and Pratik Jain in Bengaluru; Editing by Sriraj Kalluvila)