Valeant Pharmaceuticals International Inc. said Thursday that a newly approved generic version of one of its drugs could significantly reduce its profits this year.

Mylan Inc. on Wednesday received final approval from the U.S. Food and Drug Administration to sell the first generic version of Valeant's Zovirax ointment, which is used in the treatment of herpes. It will start shipping the product immediately.

Valeant said that while the timing of the approval wasn't certain, the company knew it was coming and prepared for it. The Canadian company announced plans to launch its own generic version of the drug immediately.

But Valeant said that it didn't factor the approval into its original budget expectations and warned that the event could reduce its 2013 profit by between 30 and 40 cents per share.

It added that other actions, including several product acquisitions and the repricing of its term loan debt, which have taken place since it announced its financial guidance in January, could partially offset the effects of the Zovirax genericization. 

Valeant said in January that it expected a 2013 profit of $5.45 to $5.75 per share on $4.4 billion to $4.8 billion in revenue. Analysts polled by FactSet currently expect a profit of $5.63 per share on $4.62 billion in revenue.

The company said Thursday that it will update its 2013 guidance when it releases its first quarter financial results in May.

Valeant's U.S. shares fell $1.81, or 2.5 percent, to $70.06 in morning trading.