Sen. Amy Klobuchar (D-Minn.) wrote to the CEOs of Novo Nordisk, Sanofi and Eli Lilly asking them to justify recent steep price hikes for insulin medication. The cost of insulin has increased more than threefold in the last decade, which, Klobuchar said, is likely due in large part to the relative lack of competition, while insulin manufacturers have failed to document a corresponding increase in production costs.