PARIS — The French drug maker Sanofi said 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 hammered earnings.

Sanofi, the parent of Genzyme Corp., said net profit was $593 million in the October-December quarter. Sales were flat at $11.39 billion. Restructuring costs rose over $133.8 million to $1.1 billion.