The Food and Drug Administration approved Vertex Pharmaceuticals Inc.'s hepatitis C drug Incivek Monday, making it the second new treatment to be approved in the last two weeks.

Incivek is a highly anticipated pill that is expected to have annual sales in the billions. It is approved for patients who have some liver damage from hepatitis C who either have not been treated, or were not cured by other drugs. Patients on Incivek take two pills three times per day. The Cambridge, Mass., company has already started promoting the drug in advance of approval, and it said Incivek will be available in pharmacies later this week.

The company says a 12-week course of treatment will cost $49,200, compared to $30,000 for standard therapies.

Hepatitis C is an infectious disease that is spread through the blood, including by sharing needles or having sex with an infected person. Vertex said about 4 million people in the U.S. have the disease, and many people do not know they are infected. Hepatitis C can cause liver damage, cirrhosis, liver failure or cancer. Incivek and Merck & Co.'s Victrelis, which was approved earlier this month, are the first new breakthrough treatments for the liver disease to be approved in 20 years.

In clinical trials, patients were treated with a combination of Incivek and standard therapies for 12 weeks. They continued on the standard treatments for another 36 weeks, but many of them were cured within 24 weeks. Vertex said about 79 percent of previously untreated patients were cured after treatment with Incivek. The drug was also much more effective in patients who had relapsed, had some response but not a cure, or had no response to other drugs.

Both Incivek and Victrelis block an enzyme that helps the virus reproduce. Incivek is seen as the more effective of the two drugs and is expected to have greater sales. Victrelis is a pill taken three times per day.

The most common side effects of Incivek are fatigue, itching, nausea, diarrhea, vomiting, taste changes, and anal or rectal problems. More serious side effects include rash, anemia, low red blood cell count, and birth defects in pregnant women. The side effects of standard treatments — including the IV drug pegylated interferon and the pill ribavirin — can include months of side effects, but less than half of patients are cured.

Vertex owns the North American marketing rights to Incivek, also known as telaprevir, and is seeking marketing approval in other countries through partnerships, including an agreement with Johnson & Johnson. The company said it has a 115-person sales team to support the drug, and will give Incivek for free to people with no health insurance and annual household income of less than $100,000. It will also cover some co-pay or co-insurance costs.

Shares of Vertex rose 20 cents to $55.20 in midday trading.