Hypoglycemia: a review of definitions used in clinical trials evaluating antihyperglycemic drugs for diabetes

OBJECTIVE: To understand the severity and potential impact of heterogeneity in definitions of hypoglycemia used in diabetes research, we aimed to review the hypoglycemia definitions adopted in randomized controlled trials (RCTs). METHODS: We reviewed 109 RCTs included in the Canadian Agency for Drugs and Technologies in Health reports for the second- and third-line therapy for the patients with type 2 diabetes (T2D). RESULTS: Nearly 60% (n=66) of the studies reviewed presented the definitions for overall hypoglycemia, and another 20% (n=22) of the studies reported the results for hypoglycemia but did not report a definition. Among these 66 studies, only 9 (14%) followed the American Diabetes Association/European Medicines Agency specified guidelines to define hypoglycemia, with an exact threshold of plasma glucose ≤3.9 mmol/L. Fifty-two of the 66 studies (79%) used a threshold considerably lower than the recommended ≤3.9 mmol/L, and 16 studies used a threshold between 3.8 and 4.0 mmol/L. The proportion of the trials that used a cutoff value of <3.1 mmol/L appeared to be slightly similar among the more commonly used non-insulin treatments, GLP-1s (7 of 18 [39%]), thiazolidinediones (TZDs; 6 of 11 [55%]), DPP-4s (12 of 19 [64%]), and sulfonylureas (11 of 20 [55%]). Among trials with intermediate-long-acting insulins (neutral protamine Hagedorn insulin, detemir, glargine), 7 of 26 trials (27%) used a cutoff of <3.1 mmol/L. The definition of severe hypoglycemia was also subject to substantial heterogeneity, in both the utilized threshold and accompanying soft definitions. CONCLUSION: This review demonstrates that substantial heterogeneity exists in the definition of overall, severe/major, and nocturnal hypoglycemia across RCTs investigating T2D interventions.