Background Pectoral nerve blocks (PECS) provide effective regional analgesia after mastectomy, but the optimal adjuvant remains unclear. This study compared ketamine and magnesium sulphate as adjuvants to bupivacaine in PECS blocks. Methods In this randomized, double-blind trial, 72 patients scheduled for modified radical mastectomy were randomized into 3 equal groups (n = 24). Group A received 0.25% bupivacaine with saline (control); Groups B and C received bupivacaine with ketamine or magnesium sulphate, respectively. The primary outcome was time to first rescue analgesia; secondary outcomes included 24-hour pethidine consumption, postoperative pain (Visual Analog Scale, VAS), and hemodynamic parameters. Results Baseline and intraoperative parameters were comparable among groups. Postoperatively, the control group had significantly higher heart rate, mean arterial pressure, and respiratory rate than both adjuvant groups during the first 12 hours. VAS scores were lower in both adjuvant groups than in the control group, and lower with ketamine than with magnesium sulphate from 1 to 8 hours. Both adjuvants significantly prolonged time to first rescue analgesia and reduced 24-hour pethidine consumption compared with control. Ketamine achieved a longer median time to first rescue analgesia (10 [IQR 8-12] vs. 8 [IQR 4-8] hours; P = .023) and lower median pethidine consumption (75 [IQR 50-100] vs. 100 [IQR 100-112.5] mg; P = .018) than magnesium sulphate. Conclusion Ketamine and magnesium sulphate both improve postoperative analgesia and reduce opioid consumption after mastectomy. Ketamine was superior to magnesium sulphate and may be the preferred adjuvant, though larger trials are needed.
