WASHINGTON - Mylan CEO Heather Bresch infuriated lawmakers as she tried to explain steep cost increases of her company's life-saving EpiPens.

Outraged Republican and Democratic lawmakers on Wednesday grilled Bresch about the emergency allergy shot's sky-high price and the profits for a company with sales in excess of $11 billion. The list price of EpiPens has grown to $608 for a two-pack, an increase of more than 500 percent since 2007.

In almost four hours of questioning, the soft-spoken CEO at times seemed unsure when asked questions about the company's finances and profits, angering lawmakers.

House Oversight and Government Reform Chairman Rep. Jason Chaffetz of Utah said he didn't believe Bresch was being candid with lawmakers.

Bresch said she wishes Mylan had "better anticipated the magnitude and acceleration" of rising prices.