Background: It has been observed that the efficacy of dipeptidyl peptidase-4 (DPP-4) inhibitors as compared to\nthe placebo groups in some clinical trials conducted in China is weaker than that in trials conducted outside China,\nleading to the suspicion that this may be caused by differential Glycosylated Hemoglobin (HbA1c) response in the\nplacebo arm of DPP-4 inhibitor clinical trials conducted in China compared to other countries.\nMethods: We searched published articles and other documents related to phase III placebo-control trials of DPP-4\ninhibitors in Type 2 diabetes mellitus (T2DM). We included studies from different countries and compared those\nconducted in China to those conducted in other countries. Meta-regression analysis was used to analyze the HbA1c\nresponse in the placebo arms.\nResults: A total of 66 studies met the inclusion criteria and 10 were conducted within China. There were a total of 8303\nparticipants (mean age 56, male 57 %) in placebo groups. The pooled change in HbA1c for the placebo groups of 10\ntrials conducted in patients with T2DM in China was 0.26 % (95 % CI [-0.36 %, -0.16 %], p-value < 0.001), compared to\n0.015 % (95 % CI [-0.05 %, 0.08 %], p-value is 0.637) for 56 trials conducted outside of China. The difference of placebo\neffect between trials conducted in and outside China is -0.273 % (95 % CI [-0.42 %, -0.13 %], p-value is less than 0.001)\nwhile after excluding trials conducted in Japan, the difference is -0.203 % (95 % CI [-0.35 %, -0.06 %], p-value is 0.005).\nThey are both statistically significant.\nConclusions: The meta-analysis in the article demonstrates that there is statistically significant difference in the HbA1c\nresponse in the placebo arm of DPP-4 inhibitor clinical trials conducted in China compared to other countries. This\ndifferential HbA1c response in the placebo arm should be taken into consideration by both experimenters and medical\ndecision makers when future DPP-4 studies are conducted in China.
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