Federal health scientists say Forest Laboratories' hypertension drug Bystolic should not be approved for a new use in patients at risk for heart failure.

The Food and Drug Administration says results from a company study "lack robustness," and don't give a clear picture of the drug's effectiveness.

New York-based Forest conducted a study called SENIORS which tracked 2,000 elderly patients at risk for heart failure who received either standard drug therapy or treatment with Bystolic.

The difference in cardiac death and hospitalization between the groups was not statistically significant, according to the FDA.

Agency reviewers also complain that the company made several adjustments to the design of the trial while it was ongoing.