Type 2 diabetes (T2D) is a chronic, progressive disease marked by ongoing decline in insulin sensitivity and beta-cell function over time. Clinical trials have shown that lowering A1C to ∼7.0% (53 mmol/mol), especially after an early diagnosis, can markedly reduce the long-term complications of T2D. Metformin has become the generally recommended first therapeutic agent in treating T2D due to the drug’s long-term experience, effectiveness, and avoidance of hypoglycemia or weight gain. However, it is clear that additional agents are necessary to regain glucose control when metformin eventually fails due to the progressive nature of the disease.
Insufficient data on comparative efficacy and durability of effect has led to uncertainty in recommendations for the preferred second agent. Comparative effectiveness has been reported primarily in industry-sponsored trials of relatively short duration. With this in mind, the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) sponsored the Glycemia Reduction Approaches in Diabetes: A Comparative Effectiveness (GRADE) Study. This landmark, randomized controlled study was initiated in 2013, enrolling patients on metformin alone within 10 years of diagnosis of T2D. It involved 36 research sites in the United States with a mean follow-up of 5 years. The participants were randomized to adding a dipeptidyl peptidase 4 (DPP-4) inhibitor (sitagliptin), a sulfonylurea (glimepiride), basal insulin (glargine), or a glucagon-like peptide 1 receptor agonist (GLP-1 RA) (liraglutide), with the primary outcome being time to A1C over 7.0%.
The GRADE study was unique in several ways: its size, scope, length, and the fact that the financial support and design planning stemmed from a U34 planning grant from the NIDDK. The study population of 5047 participants was very diverse, reflecting the population affected by T2D. A mix of racial and ethnic groups were represented, including 19.8% Black participants and 18.6% Hispanic participants. It is unlikely that a similar comparative effectiveness trial of pharmacologic treatment of T2D will be performed again in the future, considering the high costs and length of time required for such a study amid the dynamic drug development environment today. In fact, the final implementation of study results is somewhat complicated by the subsequent approval of GLP-1 RAs of greater efficacy, weight loss, and convenience, as well as sodium-glucose cotransporter 2 (SGLT2) inhibitors and, most recently, a dual GLP-1/gastric inhibitory polypeptide (GIP) receptor agonist (tirzepatide). Many of these newer agents have demonstrated nonglycemic benefits, such as reduced risk of cardiovascular (CV) events or reduced progression of renal disease. The findings from the GRADE study, however, did provide important insight on the long-term management of T2D.
The GRADE study was the first to compare the efficacy of 4 US Food and Drug Administration–approved drugs for T2D in maintaining blood glucose levels for the longest amount of time in patients with T2D. It also monitored microvascular complications, CV events, and adverse drug effects.
An important message of the study that may be overlooked is that all of the studied agents’ ability to maintain an A1C under 7.0% was quite low—as 71% of all participants reached the primary outcome by 5 years; the best results for a group were 67% for glargine and 68% for liraglutide. In general, the results showed that liraglutide and insulin glargine were superior to glimepiride and sitagliptin in controlling blood sugars. They provided approximately 6 months’ more time with blood glucose levels in the desired range compared with sitagliptin, which was shown to provide the least amount of time in maintaining glucose levels. Fifty-five percent of the sitagliptin group experienced the primary outcome at 1 year. Sitagliptin was particularly ineffective for the patient subgroup with an A1C at baseline of 7.8% or higher, where 70% reached the primary outcome in 1 year. The results were uniform regarding age, race, sex, and ethnicity of the trial participants. The intention-to-treat design of the study limits the conclusions about A1C differences, as failure to maintain an A1C under 7.5% required addition of prandial insulin for the glargine group and the addition of glargine to the other 3 groups. Although subjects receiving glargine had an initial glucose-lowering effect that was less than that seen with liraglutide, the ability to keep titrating the glargine likely had an impact on the long-term benefit of that agent. When the glargine group neared or in some cases even passed the secondary outcome A1C level of 7.5%, the basal insulin was increased to lower the A1C, sometimes even when the protocol would recommend adding prandial insulin.