Double-blind, randomized, multicentre, and active comparator controlled investigation of the effect of pioglitazone, metformin, and the combination of both on cardiovascular risk in patients with type 2 diabetes receiving stable basal insulin therapy: the PIOCOMB study - Hanefeld, M; Pfutzner, A; Forst, T; Kleine, I; Fuchs, W (Cardiovasc Diabetol, 2011)