Idenix Pharmaceuticals Inc., a maker of drugs to treat viral and infectious diseases, on Friday reported a wider third-quarter loss as expenses rose sharply.

The company, which earlier this week received approval for a hepatitis B drug, posted a loss of $19.7 million, or 35 cents per share, missing Wall Street's consensus estimate of a 34-cent loss by a penny. Last year, the loss totaled $13.7 million, or 28 cents per share.

Revenue increased 26 percent to $19.6 million from $15.6 million, falling short of the average analyst estimate of $22.1 million.

Research and development costs rose to $26.1 million from $21.5 million, while selling and administrative expenses jumped 77 percent to $15.9 million.

Idenix said it expects to finish the year with $170 million to $190 million in cash, cash equivalents and marketable securities.

The company's shares added 9 cents to $9.97 in recent trading on the Nasdaq.