Eli Lilly

(LLY) - Get Report

said it's weighing its options for the future of ruboxistaurin mesylate, an experimental treatment for diabetic retinopathy, in light of a request by the Food and Drug Administration for an additional phase III clinical trial.

The FDA said it wants additional efficacy data before it will consider approving the molecule for the treatment of moderate to severe nonproliferative diabetic retinopathy. Lilly believes the trial would require up to five years to complete.

Last month, Lilly received conditional approval from the FDA, meaning it needed to provide the agency with additional information before it would be granted full clearance for the drug.

"We are certainly disappointed with this communication from the FDA," Lilly said. "Diabetic retinopathy is a significant unmet medical need to which we have devoted more than a decade of clinical research with no guarantee of approval."

Clinical trials for ruboxistaurin will continue while Lilly evaluates its further development. Ruboxistaurin, whose proposed brand name is Arxxant, was submitted to the FDA in February.

For now, Lilly doesn't plan to withdraw the drug's application. Shares of Lilly were losing 35 cents, or 0.6%, to $56.97.