(Reuters) – The U.S. Food and Drug Administration is looking into whether Daiichi Sankyo’s (4568.T) blood pressure medicine Benicar increases the risk of heart-related death, although the agency said it still believes the benefits of the drug outweigh its potential risks.

The FDA said it is evaluating data from a pair of clinical trials in which diabetes patients taking the drug, known chemically as olmesartan, had a higher rate of death from heart related causes compared with patients taking a placebo.

In a safety notice posted on Friday, the agency cautioned that it has not concluded that Benicar increases the risk of death, and Daiichi has expressed its confidence in the drug.

In addition to reviewing data from the two studies, the FDA said it is considering additional ways to assess the cardiovascular effects of Benicar.

In the long-term trials, patients with type 2 diabetes were given either Benicar or placebo to determine whether Benicar would slow the progression of kidney disease or progression of the diabetes.

In the larger of the two trials, Benicar did appear to slow the onset of kidney disease, Daiichi said.

But an unexpected finding in both trials was a greater number of deaths from heart attack, stroke or sudden death in the Benicar-treated patients compared with those who took a placebo, the FDA said.

“Olmesartan has been around for a long time, and the class of drugs has been around for a very long time. We’ve been very confident, as the FDA has been, in both the efficacy and the safety,” Daiichi’s chief scientific officer, Dr. Glenn Gormley, said in a telephone interview.

There are several classes of drugs that work through different mechanisms to treat high blood pressure. Benicar belongs to a class known as angiotensin receptor blockers, or ARBs, that are also used to prevent kidney failure.

Other ARBs include Merck & Co’s (MRK.N) Cozaar and Novartis AG’s (NOVN.VX) Diovan.

“There was a numerical imbalance in some of the cardiovascular side effects,” Gormley said. “We’ve never seen that before in other studies and I don’t think we’ve seen that with other ARBs.”

In the larger of the two studies, which included more than 4,400 patients divided about evenly between those taking Benicar or placebo, there were 15 heart-related deaths in the drug group versus three on placebo.

In the other 557-patient study, there were 10 heart deaths in the Benicar group compared with three on placebo.

“It’s a very small number and the FDA would just like to understand it better, as we would,” said Gormley, adding that the company is working with the agency to help with the analysis.

The FDA is encouraging healthcare professionals and patients to report adverse events or side effects related to the use of Benicar. (Reporting by Bill Berkrot; Editing by Tim Dobbyn and Gerald E. McCormick)