Efficacy of GLP-1 Receptor Agonists and DPP-4 Inhibitors: Meta-analysis and Systematic Review

Background: Considerable clinical data on the treatment of type 2 diabetes with incretin-based therapies (glucagon-like peptide 1 receptor agonists [GLP-1RAs] and dipeptidyl-peptidase IV [DPP-4] inhibitors) are available.

Objective: This meta-analysis was performed to support the understanding of the overall evidence by summarizing the findings from studies of the incretin-based therapies.

Methods: The MEDLINE, EMBASE, BIOSIS, and BIOSIS trial databases were searched for relevant literature published between January 1, 1990, and June 30, 2011. Search terms included GLP-1, DPP-4, the names of drugs that have been approved by the US Food and Drug Administration for the treatment of diabetes, and the names of drugs that have not been approved but are in late-stage research. Studies were included if they were randomized controlled trials of 12 to 52 weeks' duration and having change from baseline in hemoglobin (Hb) A(1c) as the primary end point. The random effects meta-analyses models examined HbA(1c), fasting plasma glucose (FPG), and body weight for individual therapies, but did not compare effects between therapies.

Results: The reviewers identified 362 unique clinical studies, of which 80 were eligible for inclusion in the present meta-analysis. Mean baseline HbA(1c) values ranged from 7.4% to 10.3% (GLP-1RA studies) and 7.2% to 9.3% (DPP-4 inhibitor studies). The highest maintenance doses of the GLP-1RAs and the DPP-4 inhibitors were associated with changes from baseline in mean HbA(1c) of -1.1% to -1.6% and -0.6% to -1.1%, respectively. Mean reductions in FPG with exenatide once weekly (QW) or liraglutide once daily were apparently greater than those with exenatide twice daily (BID) and the DPP-4 inhibitors, with the exception of vildagliptin. Mean weight losses with the GLP-1RAs and the DPP-4 inhibitors were >-2.0 and -0.2 to -0.6 kg, respectively. The limitations of the present analysis included a lack of adjustment for placebo use and interstudy heterogeneity associated with differences in methodology (eg, management of concurrent medications, blinding, criteria for treatment discontinuation).

Conclusions: All of the incretin-based therapies in the present meta-analysis were associated with significant reductions from baseline in HbA(1c) and FPG. Further direct comparative studies between the GLP-1RAs and the DPP-4 inhibitors and within the GLP-1RA class are justified.