OAD agents effective in reducing hemoglobin levels up to 1.5%

Oral antidiabetic (OAD) agents generally result in a maximum 1.5% drop in hemoglobin (Hb) A_1C levels, with sulfonylureas and thiazolidinediones having a slightly more beneficial effect than other classes of oral agents, according to research published in the August issue of Diabetes Care and reported by HealthDay News.

Diana Sherifali, RN, of McMaster University in Hamilton, Ontario, and her colleagues conducted a systematic review and meta-analysis of 61 randomized controlled trials involving more than 26,000 patients. Researchers studied the effect of OAD agents on HbA_1C levels. The analysis was conducted because previous reviews of the topic included studies of various designs and methodological approaches.

The reviewed trials included 15,760 participants randomly assigned to an intervention OAD agent and 10,607 randomly assigned to placebo. The researchers found that thiazolidinediones and sulfonylureas lowered HbA_1C levels by about 1.0% to 1.25%, while most OAD agents lowered them by 0.5% to 1.25%.

Using meta-regression analysis, for each 1% higher the baseline pretreatment HbA_1C level, a 0.5 greater decrease in A_1C level was obtained after 6 months of treatment, Sherifali said. The authors concluded that the benefit of an OAD agent was most apparent in the first 4 to 6 months of therapy, and that a 1.5% fall in HbA_1C level was likely to be the maximum, she added.

“This effect was fairly consistent between OAD classes with sulfonylureas and thiazolidinediones having the greatest reduction in [A1C],” the authors wrote. “The meta-regression analysis numerically demonstrated a small effect of baseline HbA_1C on the fall of HbA_1C with OAD treatment. Further carefully conducted OAD trials are needed to account for [the] combinations of OAD drug use and its impact on HbA_1C levels, the effectiveness of long-term OAD use on HbA_1C levels, and adverse and hypoglycemic events.”

Sherifali said she would like to see long-term follow-up studies that examine the effectiveness of combination OAD therapies, because this is what guidelines and standards of care recommend. She also wants to see studies that examine adverse events associated with single-use OAD and combination therapies over time.

The study was funded by an unrestricted grant from Merck Frosst.