The Impact of Metformin on Postoperative Opioid Consumption and Patient Reported Outcomes after Lumbar Fusion.

Abstract

Retrospective cohort. To examine metformin use on postoperative outcomes amongst patients with diabetes undergoing lumbar fusion. Several animal studies have demonstrated that metformin, a first-line treatment for type 2 diabetes (T2DM), can attenuate neuropathic pain via decreased activation of microglia and suppression of inflammatory signaling. Adult diabetic patients who underwent a 1-2-level posterior lumbar decompression and fusion (PLDF) (2017-2023) were identified and demographics, surgical data, metformin use/dosage, opioid consumption and patient-reported outcome measures (PROMs) collected. Statistical analysis was performed with alpha set at 0.05. Of the 299 diabetic patients who underwent a 1-2 level PLDF, 203 (67.9%) were taking metformin. There were no differences in morphine milligram equivalents (MMEs) in the 30 days prior to or the 30 days after surgery between groups. Patients on metformin had a lower Elixhauser (2.26 ± 1.48 vs. 2.79 ± 1.71; P=0.005), lower HgbA1c (7.15± 1.12 vs. 7.48± 1.59; p = 0.018), and fewer females (59.4% versus 42.4%, P= 0.009) but were otherwise demographically/surgically similar. Despite both groups having similar preoperative opioid use, metformin use was associated with lower MMEs at 30-90 days (31.8 ± 60.4 vs. 52.0 ± 92.0; P=0.018 and 90-365 days (65.0 ± 183 vs. 129 ± 292 MME; P=0.001), and greater improvement from pre- to postoperative PCS at 6 months (5.12 ± 8.96 vs -1.34 ± 8.57, P=0.048) and at 1-year (4.96 ± 9.47 vs. -1.87 ± 7.55, P = 0.027). Linear regression analysis identified metformin use as independently predictive of fewer postoperative MMEs 30-90 days postoperatively (Estimate -16.03, CI -31.51 to -0.56; P=0.043). Metformin use was found to be independently associated with fewer MME requirements 30 days after surgery.