Klobuchar, whose own daughter uses an EpiPen, noted that Mylan has seen one competitor, Sanofi's Auvi-Q, exit the market last year due to a recall, and Teva's generic version failed to receive regulatory approval.
The senator has called for the Federal Trade Commission to probe the price hikes. Sen. Chuck Grassley, R-Iowa, the head of the Senate Judiciary Committee, has written Mylan asking how EpiPen's prices were determined.
Drug manufacturers defend rising prices, citing the high cost of years of research and development that goes into making blockbuster drugs. In an effort to provide more transparency on the cost of the drug, Mylan provided this supply chain chart.
— CNBC's Dan Mangan and Reuters contributed to this report.