Swiss pharmaceuticals firm Roche has received approval in the United States for its hepatitis C drug Pegasys.
The approval of Pegasys as a stand-alone therapy had been widely expected.
Roche is now waiting for the green light for the more-important combination therapy of Pegasys and ribavirin.
Pegasys is Roche's top new drug this year, and the company is counting on it to help revive sales, which have been flat in the past three quarters.
It is forecasting that annual sales of the drug may peak at around SFr1.5 billion ($1 billion).
The US Food and Drug Administration approved Pegasys for treating adult patients with chronic Hepatitis C, an often-fatal viral liver infection. The drug is administered once a week as an injection.
Chairman and CEO Franz Humer said approval of the Pegasys combination therapy was expected in the near future.
"We are en route," Humer said. "We obtained a fast-track review from the FDA for this filing, so that we are counting on approval before the end of the year."
Roche said the US was a "very important market" for the drug, with almost 2.7 million Americans suffering from chronic Hepatitis C.
"I am convinced that in a few years' time we will be the market leader in this area," Humer said.
Pegasys has already been approved in more than 50 countries.
It was first used in Switzerland a year ago and now enjoys a market share of 75 per cent.
swissinfo with agencies
Pegasys is normally used in combination with ribavirin to treat chronic Hepatitis C.
The drug was first introduced in Switzerland a year ago and now enjoys a 75 per cent market share.
Pegasys is approved for use in more than 50 countries.
In the US, 2.7 million people suffer from chronic Hepatitis C.