Thirty-eight RCTs (n=16,502 participants) were included in the review. Thirty-four RCTs were double-blind.
Glycaemic control: All treatments were shown to produce a statistically significant reduction in glycated haemoglobin compared with placebo: vildagliptin (unadjusted WMD -0.67, 95% CI -0.83 to -0.52; 11 RCTs); sitagliptin (unadjusted WMD -0.79, 95% CI -0.93 to -0.65; 12 RCTs); exenatide (unadjusted WMD -0.75, 95% CI -0.83 to -0.67; eight RCTs); and liraglutide (unadjusted WMD -1.03, 95% CI -1.16 to -0.90; seven RCTs).
Weight: Vildagliptin (unadjusted WMD 0.56, 95% CI 0.27 to 0.84) and sitagliptin (unadjusted WMD 0.60, 95% CI 0.33 to 0.87) were both associated with a significant increase in weight when compared with placebo. Exenatide treatment was associated with significantly decreased weight when compared with placebo (unadjusted WMD -1.10, 95% CI -1.32 to -0.88). There was no significant difference between weight in liraglutide and placebo treated participants.
Hypoglycaemia: There was no significant difference between vildagliptin and placebo in the number of participants who reported hypoglycaemic episodes. Participants treated with sitagliptin (unadjusted RR 2.56, 95% CI 1.23 to 5.33), exenatide (unadjusted RR 2.40, 95% CI 1.39 to 4.11) and liraglutide (unadjusted RR 1.69, 95% CI 1.00 to 2.86) were more likely to experience hypoglycaemia compared with participants randomised to placebo.
There were a few instances where the covariates evaluated in meta-regression had a statistically significant impact on the outcomes.