The authors conducted a post hoc analysis of data from 3 randomized studies that compared saxagliptin versus placebo as initial combination therapy with metformin for 24 weeks ( N = 648 ) and versus placebo as an add-on to insulin with and without metformin for 24 weeks ( N = 455 ) , and assessed noninferiority to glipizide as an add-on to metformin for 52 weeks ( N = 858 ) .