French drug maker Sanofi says its net profit was more than halved in the fourth quarter from a year earlier as mounting restructuring costs and patent losses on key drugs combined to hammer earnings.

Sanofi said Thursday that its net profit was (EURO)438 million ($593 million) in the October-December quarter, down from (EURO)1.5 billion a year earlier. Sales were flat at (EURO)8.5 billion in the quarter. Restructuring costs rose over (EURO)100 million to (EURO)834 million.

The company blamed the loss of U.S. patent protection on key drugs Plavix and Avapro cost it (EURO)1.3 billion last year.

Sanofi warned its core earnings per share could fall up to 5 percent this year, after a 12.8 percent drop in 2012.