Anadys Pharmaceuticals Inc said its experimental hepatitis C drug, ANA598, showed positive preliminary results in a mid-stage trial, sending its shares up as much as 9 percent in premarket trade.

The company said 56 percent of the patients receiving the drug showed undetectable levels of the virus at four weeks, compared to 20 percent of patients who received the dummy drug.

Anadys said, in the trial its key drug was given in combination with pegylated interferon and ribavirin, which is the current standard of care, at a dosage level of 200 milligram bid and analyzed at four weeks.

An independent Data Monitoring Committee has recommended escalating to the second dose level, 400 mg bid, the company said in a statement.

Anadys said there were eight patients who reported rash through the interim analysis data, seven mild and one moderate, adding that there were no discontinuations due to adverse events.

The drug had faced safety concerns earlier this year after three patients dropped out of a safety study as they developed a rash.

Shares of the company rose 9 percent to $3.20 in premarket trade. They had closed at $2.94 Wednesday on Nasdaq.