Shares of the Aliso Viejo, Calif., company, which makes neurology and dermatology products, fell $1.23, or 10.4 percent, to close at $10.65 Monday, having hit a low earlier in the day of $10.35. That level is below its previous 52-week low of $11.61 and is the lowest level since May 2003.

On Thursday, the drug maker reported it swung to a loss in the third quarter and said it is selling its hepatitis C treatment Infergen. Sales were pressured by alliance revenue, which decreased 33 percent in the third quarter. The company blamed competition in Europe and Japan for hepatitis C drug ribavirin and the discontinuation of ribavirin royalties from Roche.

In a note to investors Monday, analyst John Boris downgraded Valeant to "Underperform" from "Peer Perform" and lowered his estimates on the company.

In lowering his ribavirin royalty estimates, Boris shaved off $1 million to $65 million for 2007.

The analyst also cut his product sales expectations for 2007 to 2009 after removing Infergen from his model.

Boris noted the company lowered its 2007 and 2008 product sales expectations, excluding Infergen, to low single-digit growth in the range of 5 percent to 6 percent. Boris expects growth of 2 percent in 2007 and 4 percent in 2008.