The Impact of Metformin on Postoperative Opioid Consumption and Patient-Reported Outcomes After Lumbar Fusion

Retrospective cohort. To examine metformin use on postoperative outcomes among 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 through 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) were 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 before 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% vs. 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 to 90 days (31.8±60.4 vs. 52.0±92.0; P  = 0.018) and 90-365 d (65.0±183 vs. 129±292 MME; P  = 0.001), and greater improvement from preoperative 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 to 90 days postoperatively (estimate -16.03, 95% 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.