Analysis of Long-term Follow-up of a Randomized Clinical Trial With Departures From Assigned Treatments: Estimation of Metformin Effects on Diabetes and Its Complications in the Diabetes Prevention Program Outcomes Study

William C. Knowler, Consultant, Department of Biostatistics and Bioinformatics, Milken Institute School of Public Health, The George Washington University, Rockville, MD.
Qing Pan, Department of Biostatistics and Bioinformatics, Milken Institute School of Public Health, The George Washington University, Rockville, MD.
Shiyu Shu, Department of Biostatistics and Bioinformatics, Milken Institute School of Public Health, The George Washington University, Rockville, MD.
Mark T. Tripputi, Department of Biostatistics and Bioinformatics, Milken Institute School of Public Health, The George Washington University, Rockville, MD.
Dana Dabelea, Departments of Pediatrics and Epidemiology and Lifecourse Epidemiology of Adiposity and Diabetes (LEAD) Center, Colorado School of Public Health, University of Colorado Anschutz Medical Campus, Aurora, CO.
Sharon L. Edelstein, Department of Biostatistics and Bioinformatics, Milken Institute School of Public Health, The George Washington University, Rockville, MD.
Steven E. Kahn, Division of Metabolism, Endocrinology and Nutrition, University of Washington, and VA Puget Sound Health Care System, Seattle, WA.
Shihchen Kuo, Division of Metabolism, Endocrinology, and Diabetes, Department of Internal Medicine, University of Michigan, Ann Arbor, MI.
José A. Luchsinger, Departments of Medicine and Epidemiology, Columbia University Irving Medical Center, New York, NY.
Vallabh Shah, Department of Internal Medicine, Health Sciences Center, University of New Mexico, Albuquerque, NM.
Amisha Wallia, Division of Endocrinology, Metabolism and Molecular Medicine, Department of Medicine, Feinberg School of Medicine, Northwestern University, Chicago, IL.
Marinella Temprosa, Department of Biostatistics and Bioinformatics, Milken Institute School of Public Health, The George Washington University, Rockville, MD.

Document Type

Journal Article

Publication Date

8-26-2025

Journal

Diabetes care

DOI

10.2337/dci25-0032

Abstract

The Diabetes Prevention Program (DPP) was a 3-year randomized clinical trial (RCT) with evaluation of lifestyle and metformin interventions compared with placebo for diabetes prevention in high-risk adults. Both interventions significantly reduced diabetes incidence, prompting the long-term Diabetes Prevention Program Outcomes Study (DPPOS) to assess the progression of diabetes and its complications over 22 years. During follow-up, departures from the original metformin or placebo assignment occurred primarily because of development of diabetes that, by protocol, was managed by clinicians outside the study, after participants developed diabetes with HbA1c ≥7.0%. Diabetes development led to changes in metformin treatment and addition of other glucose-lowering therapies. Using statistical methods designed to estimate intervention effects despite these deviations, we consistently found that metformin reduced diabetes incidence. However, using these methods to evaluate whether use of metformin for prediabetes confers continued benefits after diabetes diagnosis did not substantially change the conclusions from those of the simpler intention-to-treat analysis that did not account for treatment changes. All of the analytic methods used resulted in similar metformin effect estimates with 95% CIs for hazard ratios including 1.0 (no effect) for all outcomes except for diabetes incidence. Elucidating metformin's long-term role in mitigating diabetes-related complications beyond its effects on diabetes prevention is challenging.

Department

Biostatistics and Bioinformatics

Link to Full Text

Share

COinS