(Reuters) - Shares of Valeant Pharmaceuticals International Inc (>> Valeant Pharmaceuticals Intl Inc) (>> Valeant Pharmaceuticals Intl Inc) jumped 6 percent on Friday, after the company responded to criticism by Democratic presidential contender Hillary Clinton over price hikes for its migraine drug.

The stock had tumbled Thursday, pressured by a blog post by Clinton's campaign that detailed exorbitant price increases for the drug, D.H.E. 45.

At an Iowa town hall over the weekend, Clinton had said the list price for 10 vials of D.H.E. 45 had increased to more than $14,000 in December, from just over $3,000 in June 2014.

Valeant said Friday in a statement that a generic version of the drug, made by Perrigo Company PLC (>> Perrigo Company PLC), was widely available and outsold the branded product. Valeant said it has less than 1 percent market share for the drug.

"Whenever the sales volume of a drug declines, manufacturers must consider pricing adjustments to keep production of the drug viable," Valeant said on its website. "Patients are able to choose generic versions of the drug, however, at significantly lower prices."

Valeant shares jumped 6 percent in New York and Toronto in morning trading, after falling about 9 percent on Thursday.

Perrigo stock was up slightly.

D.H.E. 45, or dihydroergotamine, is an injectable analgesic.

Valeant, based in Laval, Quebec, has been under pressure since last year as cracks appeared in its business model of acquiring older drugs, steeply increasing their U.S. price, and using aggressive methods to overcome insurer barriers to reimbursing its medicines.

(Reporting by Rod Nickel in Winnipeg, Manitoba; Editing by Bernadette Baum)