Efficacy and safety of sitagliptin added to ongoing metformin and rosiglitazone combination therapy in a randomized placebo-controlled 54-week trial in patients with type 2 diabetes (一项为期54周的对持续使用二甲双胍与罗格列酮联合治疗的2型糖尿病患者加用西格列汀治疗的有效性与安全性的随机安慰剂对照研究)*: Sitagliptin plus metformin/rosiglitazone