BioCryst Pharmaceuticals says it is withdrawing its investigational new drug application for a proposed treatment of hepatitis C due to safety concerns.

The decision came after the company discussed its BCX5191 antiviral nucleoside with the Food and Drug Administration.

“The FDA indicated concerns regarding the preclinical toxicity profile of BCX5191 at exposure levels that they believe are likely to be necessary to reduce viral load in patients infected with the hepatitis C virus,” the company said in a statement. “Patient safety remains BioCryst’s highest priority.”

BioCryst (Nasdaq: BCRX) said it will conduct additional studies at lower does. ”BioCryst will then determine whether to continue development of BCX5191, based on the results of these studies,” the company said.

The company added that the FDA “has previously placed clinical holds on other nucleotides under development.”

BioCryst has had high expectations for BCX 5191, which the company aimed to develop into a drug with once-a-day dosing and fewer side effects compared to existing hepatitis C treatments.

When BioCryst discussed 2011 financial results earlier this year, the company released results of preclinical studies, which showed that BCX 5191 has the potential to be superior to a hepatitis C compound from Gilead Sciences (Nasdaq: GILD), MedCity News reported. Gilead acquired that compound and its developer, Pharmasset, for nearly $11 billion.

Hepatitis C represents a global market of more than 170 million patients. In light of the Pharmasset acquisition and pharma’s interest in the hepatitis C space, BioCryst has had hopes another pharmaceutical company will strike a deal with BioCryst to develop and commercialize BCX 5191. First, BioCryst needs to take its drug candidate into human trials, MedCity news noted.