Safety and efficacy of linagliptin as add-on therapy to metformin in patients with type 2 diabetes: a randomized, double-blind, placebo-controlled study. - Taskinen, M.-R.; Rosenstock, J.; Tamminen, I.; Kubiak, R.; Patel, S.; Dugi, K. A.; Woerle, H.-J. (Diabetes, Obesity & Metabolism, 2011)