Preop metformin associated with better postop outcomes in type 2 diabetes

A retrospective cohort study used electronic health record data from one health care system to assess postoperative mortality and readmission rates in adults who had major surgery.

Among patients with type 2 diabetes, taking metformin before major surgery was associated with better postoperative outcomes, a recent study found.

Researchers used electronic health record data from a health care system in Pennsylvania to perform a cohort study assessing postoperative mortality and readmission rates in adults with type 2 diabetes with and without a preoperative prescription for metformin. Patients who had major surgery with a hospital admission from Jan. 1, 2010, to Jan. 1, 2016, at 15 community and academic hospitals were included. Follow-up ended on Dec. 18, 2018.

Preoperative metformin was defined as at least one metformin prescription in the 180 days before the surgery and inclusion of metformin on the preoperative list of active medications. The study's primary outcomes were all-cause postoperative mortality, hospital readmission within 90 days of discharge, and preoperative inflammation, as measured by ratio of neutrophils to leukocytes. A propensity score-matched cohort was used to calculate absolute risk reductions (RRs) and adjusted hazard ratios (HRs). Results were published April 8 by JAMA Surgery.

A total of 10,088 patients with diabetes had a major surgical intervention, and of these, 5,962 (59%) had a preoperative prescription for metformin. The propensity score-matched cohort included 5,460 patients; mean age was 67.7 years, and 2,866 (53%) were women. In this cohort, an association was seen between preoperative metformin prescriptions and a reduced hazard for mortality at 90 days (adjusted HR, 0.72 [95% CI, 0.55 to 0.95]; absolute RR, 1.28% [95% CI, 0.26% to 2.31%]) and 30-day and 90-day readmission with mortality as a competing risk (adjusted RRs, 2.09% [95% CI, 0.35% to 3.82%] and 2.78% [95% CI, 0.62% to 4.95%], respectively; sub-HRs, 0.84 [95% CI, 0.72 to 0.98] and 0.86 [95% CI, 0.77 to 0.97], respectively). Patients with a preoperative metformin prescription also had less preoperative inflammation than those without (mean neutrophil-to-leukocyte ratio, 4.5 vs. 5.0; P<0.001).

The researchers noted that their retrospective study could have been affected by residual confounding, that it involved a range of surgical procedures, and that preoperative metformin dose and duration were unknown, among other limitations. They concluded that their results indicate an association between preoperative metformin and postoperative outcomes in patients with type 2 diabetes and said that these findings should be investigated further.

An accompanying commentary pointed out that the study did not control for statins and said that future research on the association of metformin and surgical outcomes should exclude patients taking statins or examine possible interactions between statins and metformin. “We would be interested in seeing a subanalysis of [the current] data set that excludes patients who were prescribed statins,” the commentary authors wrote. “These data would further solidify the role of metformin as a possible modifiable perioperative factor.”