Yu S, Schwab P, Bian B, Radican L, Tunceli K. Use of add-on treatment to Metformin monotherapy for patients with type 2 Diabetes and suboptimal glycemic control: a U.S. database study. J Manag Care Spec Pharm. 2016 Mar;22(3):272-80. doi: 10.18553/jmcp.2016.22.3.272