Have Clinical Studies Demonstrated Diabetes Prevention or Delay of Diabetes Through Early Treatment?

The incidence of type 2 diabetes continues to increase at alarming rates. Prediabetes is a state of abnormal glycemic values that are not abnormal enough to result in the diagnosis of type 2 diabetes. Significant interest in the prevention of diabetes has resulted in trials evaluating pharmacologic intervention and lifestyle intervention to prevent the development of diabetes. Controversy exists over the exact definition of diabetes prevention. Agents might possibly delay diagnosis of diabetes via pharmacologic lowering of blood glucose. Goals of diabetes prevention include decreased cardiovascular disease. Trials assessing diabetes prevention should assess 1) Impact of the study drug upon the incidence of diabetes, 2) Impact of the study drug upon diagnosis of diabetes after post-treatment washout phase, 3) Assessment of insulin sensitivity/@-cell function/insulin secretion and blood glucose, 4) Assessment of confounding factors, 5) Impact of the study drug on the occurrence of cardiovascular disease. The published studies were reviewed using these criteria. Six studies evaluating seven agents have been were reviewed. Six of the seven agents reduced diagnosis of diabetes during use, but only two demonstrated effect after washout phase. One of the two agents has been withdrawn from the market. The second agent had a short follow-up period making the results difficult to interpret. Assessment of insulin secretion at entry to trial was common, however ongoing reassessment was uncommon. All studies attempted to assess confounding factors, however stratification of drug benefit relative to amount of lifestyle modification benefit was not reported in trials. Cardiovascular benefit in the form of reduced hypertension was documented with three agents. Pharmacologic prevention of type 2 diabetes remains unproven, due in part to the difficulty distinguishing between prevention and delay. Reduction in cardiovascular benefit is unproven with most agents studied. Larger studies powered to detect cardiovascular endpoints are necessary to determine benefit of diabetes prevention.