Sept 29 (Reuters) - Valeant Pharmaceuticals International Inc, which is pursuing a hostile takeover offer for Allergan Inc, on Monday said it expects sales to rise 15 percent in the third quarter but will face a tougher fourth-quarter comparison to year-ago results.

Valeant, which completed the $8.7 billion purchase of Bausch & Lomb on Aug. 6, 2013, said its third-quarter sales reflect a weak year-ago period for the contact lens maker.

The Canadian company did not give a specific fourth-quarter forecast.

Allergan, the maker of Botox anti-wrinkle injections, has criticized Valeant's acquisition-based business model as it attempts to fend off the drugmaker's $51 billion hostile bid.

(Reporting by Susan Kelly in Chicago; Editing by Lisa Shumaker)