Because the analgesic effect of vitamin C against acute pain remains poorly addressed, this meta-analysis aimed at investigating its effectiveness against acute postoperative pain. A total of seven randomized controlled trials with placebo/normal controls were identified from PubMed, Cochrane Library, Medline, Google Scholar, and Embase databases. Pooled analysis showed a lower pain score (standardized mean difference (SMD) = -0.68, 95% CI: -1.01 to -0.36, p < 0.0001; I2 = 57%) and a lower morphine consumption (weighted mean difference (WMD) = -2.44 mg, 95% CI: -4.03 to -0.86, p = 0.003; I2 = 52%) in the vitamin group than that in the placebo group within postoperative 1-2 h. At postoperative 24 h, a lower pain score (SMD = -0.65, 95% CI: -1.11 to -0.19, p = 0.005; I2 = 81%) and lower morphine consumption (WMD = -6.74 mg, 95% CI: -9.63 to -3.84, p < 0.00001; I2 = 85%) were also noted in the vitamin group. Subgroup analyses demonstrated significant reductions in pain severity and morphine requirement immediately (1-2 h) and 24 h after surgery for patients receiving intravenous vitamin C but not in the oral subgroup. These findings showed significant reductions in pain score and opioid requirement up to postoperative 24 h, respectively, suggesting the effectiveness of perioperative vitamin C use. Further large-scale trials are warranted to elucidate its optimal intravenous dosage and effectiveness against chronic pain in the postoperative pain control setting.
Keywords: analgesic requirement; anesthesia; surgery; vitamin C.