Pharmasset hepatitis C drug meets safety goal in study

The study results were presented at the 43rd annual meeting of the European Association for the Study of the Liver in Milan.

The drug was tested in two oral doses in combination with other hepatitis C treatments over the course of four weeks. The company said the drug candidate also prompted short-term antiviral activity in patients.

The study was not designed to test effectiveness as a main goal. Phase I clinical trials are often too small to measure effectiveness with any accuracy and instead focus on safety.

Shares of Pharmasset fell 29 percent, or 2 percent, to $14.21 in afternoon trading. The stock has traded between $7.54 and $36.44 over the last 52 weeks.