Synergistic effect of the association between lidocaine and magnesium sulfate on peri-operative pain after mastectomy: A randomised, double-blind trial.

BACKGROUND: Recently, the use of venous adjuvants, such as lidocaine and magnesium sulfate, has been gaining ground in multimodal analgesia. However, no study has evaluated the impact a combination of the two drugs. OBJECTIVES: To evaluate the efficacy of venous adjuvants in reducing opioid consumption and pain scores after mastectomy. DESIGN: Randomised, double-blind, parallel-group, noninferiority clinical trial with a 1 : 1 : 1 : 1 allocation ratio. SETTING: Hospital de Base do Distrito Federal, Brasilia, Federal District, Brazil from November 2014 to December 2017. PATIENTS: One-hundred and ninety-eight patients were electively scheduled for mastectomy. Seventy-eight were excluded. INTERVENTIONS: Intra-operative infusions of remifentanil (0.1 µg kg min), lidocaine (3 mg kg h), magnesium sulfate (50 mg kg + 15 mg kg h) or lidocaine with magnesium sulfate were used. All patients received standard general anaesthesia. MAIN OUTCOME MEASURES: Peri-operative opioid consumption and pain scores. RESULTS: The patients who received both lidocaine and magnesium sulfate group (n=30) consumed less alfentanil during surgery (P < 0.001) and less dipyrone (P < 0.001) and morphine (P < 0.001) in the postoperative period. Only two patients (6.7%) in the lidocaine and magnesium sulfate group needed morphine (P < 0.001). These requirements were significantly lower when compared with patients who received remifentanil (n=30; 76.6%) and magnesium sulfate (n=30; 70%; odds ratio 46.0, 95% confidence interval 8.69 to 243.25, P < 0.001, and odds ratio 32.66, 95% confidence interval 6.37 to 167.27, P < 0.001, respectively). The patients of the lidocaine and magnesium sulfate group had lower pain scores in the first 24 h postoperatively using the numerical rating scale and verbal rating scale at discharge from the postanaesthesia care unit (P < 0.001), after 12 h (P < 0.001) and after 24 h (P < 0.001) when compared with the other three groups. CONCLUSION: Our findings suggest a synergistic effect of the use of both lidocaine and magnesium in peri-operative pain. This may be another potential strategy in the multimodal analgesia regimen. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT02309879.