Efficacy of Magnesium Sulfate Added to Local Anesthetic in a Transversus Abdominis Plane Block for Analgesia Following Total Abdominal Hysterectomy: A Randomized Trial

Pain Physician. 2017 Nov;20(7):641-647.


Background: Major abdominal surgeries are associated with severe pain, which can affect respiratory and cardiac functions if insufficiently treated; this increases postoperative morbidity.

Objective: We aim at evaluating the efficacy of magnesium sulfate as an adjuvant to local anesthetic in an ultrasound-guided transversus abdominis plane (TAP) block for postoperative analgesia in total abdominal hysterectomy.

Study design: A prospective, randomized, double-blinded clinical trial.

Setting: An academic medical center.

Methods: This study is registered at https://clinicaltrials.gov (no.: NCT02930707). This randomized, double-blinded clinical trial included 60 women undergoing total abdominal hysterectomy that were divided into 2 groups (30 patients per group). Group I received a TAP block with 20 mL per side of 0.25% bupivacaine plus 2 mL magnesium sulphate 10% (200 mg). Group II received a TAP block with 20 mL per side of 0.25% bupivacaine. Visual analog scale (VAS) scores, the time of the first analgesic request, total morphine consumption, and any side effects were assessed and recorded.

Results: The mean postoperative VAS score was significantly reduced in group I compared to group II in all of the time-points except after 10 hours. The mean time of the first request for rescue analgesia was significantly prolonged in group I (15.67 hrs.) compared to group II (7.33 hrs.) (P < 0.001), and the mean total morphine consumption, over the first 24 hours postoperatively, was significantly lower in group I (7.63 ± 2.93 mg) than in group II (16.20 ± 3.24 mg) (P < 0.001). No significant difference in side effects was observed.

Limitations: Sample size.

Conclusion: The addition of 200 mg of magnesium sulfate to bupivacaine in an ultrasound-guided TAP block significantly reduced postoperative opioid requirements, prolonged the duration of analgesia, and reduced the VAS score in patients who underwent abdominal hysterectomy, without significant side effects.

Key words: Magnesium sulfate, TAP block, postoperative pain, total abdominal hysterectomy.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Abdomen
  • Adult
  • Analgesics, Opioid / administration & dosage
  • Analgesics, Opioid / therapeutic use
  • Anesthetics, Local / therapeutic use*
  • Bupivacaine
  • Double-Blind Method
  • Female
  • Humans
  • Hysterectomy / adverse effects*
  • Magnesium Sulfate / therapeutic use*
  • Middle Aged
  • Morphine / administration & dosage
  • Morphine / therapeutic use
  • Nerve Block / methods*
  • Pain, Postoperative / drug therapy*
  • Prospective Studies
  • Ultrasonography, Interventional


  • Analgesics, Opioid
  • Anesthetics, Local
  • Magnesium Sulfate
  • Morphine
  • Bupivacaine

Associated data

  • ClinicalTrials.gov/NCT02930707