Given the number of medications available for type 2 diabetes mellitus, clinicians and patients need information about their effectiveness and safety to make informed choices. The objective of this review was to summarize the benefits and harms of medications (metformin, second-generation sulfonylureas, thiazolidinediones, meglitinides, dipeptidyl peptidase-4 [DPP-4] inhibitors, and glucagon-like peptide-1 [GLP-1] receptor agonists), as monotherapy and in combination, for the treatment of adults with type 2 diabetes.
We searched the MEDLINE, Embase, and Cochrane Central Register of Controlled Trials databases from inception through April 2010 for original English-language articles and sought unpublished data from the Food and Drug Administration and others.
Two reviewers independently screened titles to identify studies that assessed intermediate outcomes (e.g., hemoglobin A1c [HbA1c]), long-term clinical outcomes (e.g., mortality), and harms (e.g., hypoglycemia) in head-to-head monotherapy or combination therapy comparisons. Two reviewers serially extracted data for each article using standardized protocols, assessed applicability, and independently evaluated study quality.
The review included 140 randomized controlled trials and 26 observational studies. We graded evidence as low or insufficient for long-term clinical outcomes of all-cause mortality, cardiovascular disease, nephropathy, and neuropathy. Most medications lowered HbA1c on average by 1 absolute percentage point, but metformin was more efficacious than the DPP-4 inhibitors. Two-drug combinations had similar HbA1c reduction. Compared with metformin, thiazolidinediones and sulfonylureas had a more unfavorable effect on weight (mean difference of +2.6 kg). Metformin decreased low density lipoprotein cholesterol relative to pioglitazone, sulfonylureas, and DPP-4 inhibitors. Sulfonylureas had a fourfold higher risk of mild/moderate hypoglycemia compared with metformin alone, and, in combination with metformin, had more than a fivefold increased risk compared with metformin plus thiazolidinediones. Thiazolidinediones had an increased risk of congestive heart failure relative to sulfonylureas and bone fractures relative to metformin. Diarrhea occurred more often for metformin compared with thiazolidinedione users.
Comprehensive information comparing benefits and harms of diabetes medications can facilitate personalized treatment choices for patients. Although the long-term benefits and harms of diabetes medications remain unclear, the evidence supports use of metformin as a first-line agent. Comparisons of two-drug combinations showed little to no difference in HbA1c reduction, but some combinations increased risk for hypoglycemia and other adverse events.
