EXTON, Pa. (AP) — ViroPharma Inc. said Wednesday that it lost $4 million in the fourth quarter as revenue fell as generic competition eroded sales of its antibiotic Vancocin and its costs increased.

ViroPharma said sales of Vancocin fell more than 90 percent after less-expensive generic versions went on sale. Costs grew as the company made a royalty payment to French drugmaker Sanofi that was connected to Vancocin sales and it spent more money marketing its drug Cinryze which is used to treat a rare genetic disorder.

The company's loss amounted to 6 cents per share for the last three months of 2012 in contrast to net income of $53.2 million, or 65 cents per share, in the same period a year ago. If one-time costs are excluded the company said it earned 10 cents per share in the latest quarter. Revenue declined 27 percent to $106.5 million from $145.6 million.

Analysts expected earnings of 4 cents per share on $103.7 million in revenue, according to FactSet.

Sales of Vancocin, which is used to treat bacterial infections in the colon, fell to $5 million from $77.8 million a year ago. Sales of Cinryze rose 45 percent to $97 million. The drug is used to prevent and treat attacks of hereditary angioedema, a rare genetic disorder that can cause dangerous swelling of the throat or larynx.

For the year, ViroPharma said it earned $5.6 million, or 8 cents per share, down from $140.7 million, or $1.68 per share, in 2011. Revenue fell 21 percent, to $427.9 million from $544.4 million. Cinryze sales rose 30 percent to $327.1 million.

The company expects $450 million to $475 million in revenue in 2013, including $390 million to $400 million in sales of Cinryze in North America.

Analysts are forecasting $458.6 million in sales on average.

Shares of ViroPharma rose 20 cents to $25.15 in afternoon trading. They have traded in a 52-week range of $19.02 to $33.17.