Efficacy and safety of the dipeptidyl peptidase-4 inhibitor, sitagliptin, compared with the sulfonylurea, glipizide, in patients with type 2 diabetes inadequately controlled on metformin alone: a randomized, double-blind, non-inferiority trial. - Nauck,M.A.; Meininger,G.; Sheng,D. (Diabetes Obes Metab, 2007)