Magnesium Sulfate vs Lidocaine for Analgesia in Renal Colic

Patients with renal colic are often in severe pain, requiring rapid analgesia. NSAIDs are the recommended analgesic, however opioid analgesics are often needed. In this study the authors "hypothesized that in ED patients with acute renal colic, more effective analgesia would occur when either IV lidocaine or MgSO4 were added to IM diclofenac."

The Study
Toumia M et al. Magnesium Sulfate Versus Lidocaine as an Adjunct for Renal Colic in the Emergency Department: A Randomised, Double-Blind Controlled Trial. Ann Emerg Med 2024 Dec;84(6):670-677. PMID: 39033450

Bottom Line

I think this is a positive study.... maybe. It demonstrated that rescue analgesia was needed less often in the MgSO4 group and that patients achieved a more rapid decrease in pain with MgSO4, there was no difference between the 3 groups in terms of pre-determined clinical importance (pain < 1.3/10).

All three groups had a high pain score at presentation ( all > 8/10). I will usually give antiinflammatories but may give IV narcotic analgesia simultaneously, if the patient is in significant pain and 8.5/10, as was found in this study, is significant pain. 
This study won't change my practice, as I think a small dose of narcotic analgesia works very effectively and I usually won't wait too long to acutely reduce the patient's pain. I may consider using MgSo4, if the patient has allegies to narcotics, or if the pain seems to be refractory to narcotics, although there are also other options, that are probably more effective. 

What They Did

This was a prospective, double-blind, randomized clinical trial conducted in the Emergency Departments of 3 Academic Hospitals.

N = 840

Inclusion Criteria

• Patients aged 18 to 65 years with suspected acute renal colic
  • diagnosis was made by clinical suspicion or Ultrasound or CT scan  
• Patient-reported pain score of > 5 on a 10-cm numerical rating scale (NRS)

Exclusion Criteria

• Documented or suspected pregnancy
• Breastfeeding
• Allergy or contraindications to NSAIDs, MgSO4 or lidocaine
• Renal or hepatic dysfunction
• NSAIDs and/or analgesics used within 6 hours of presentation
• History of
  • bleeding diathesis
  • peptic ulcer or gastrointestinal haemorrhage
  • cardiac arrhythmia,  severe coronary artery disease
  • seizures
  • anticoagulant medication or with coagulation disorders.
  • allergy to morphine
• The presence of peritoneal sign,
• Altered mental state
• Haemodynamic instability

Patients were randomly allocated into one of three groups at a 1:1:1 ratio

All patients received 75 mg IM diclofenac.

The 3 groups then received either:

• 1g IV MgSO4 (10 mL) over 2 to 4 minutes,
• 1.5 mg/kg (10 mL) lidocaine over 2 to 4 min, or
• 10 ml IV normal saline solution over 2 to 4 minutes.

Emergency physicians, nurses, patients, and the research team were blinded to the study medication administered.

Pain intensity was monitored at  5, 10, 20, 30, 60, and 90 minutes. Those patients still rating their pain score as > 3 at 30 minutes post drug administration, were given IV morphine.

Adverse effects assessed included:

• headache
• dizziness,
• nausea, vomiting,
• dyspepsia,
• hypotension (SBP < 100 mm Hg),
• fushing,
• lightheadedness,
• pruritus.

72 hours post discharge followup was performed to assess:

• pain status and
• if the patient had returned to the ED with renal colic.

Primary Outcome

Proportion of patients achieving > 50% reduction in pain after 30 minutes.

Secondary Outcomes

• The need for rescue analgesia (morphine),
• Time to 50% pain reduction,
• Proportion of patients with with pain score > 2 at study completion (90 minutes),
• Adverse events,
• Frequency of return visit to the ED for renal colic recurrence.

What They Found

There was no difference between the 3 groups in terms of clinical importance (< 1.3cm on the 10cm pain scale). Although  > 50% or greater reduction in pain at 30 minutes was more frequent with MgSO4 compared to lidocaine or control groups.

There were less instances of rescue analgesia in the MgSO4 group but no differences in return visits to the emergency department for recurrent renal colic.

• There was no difference between the groups in terms of time required to achieve a 50% reduction in pain 21.3 minutes (MgSO4)
• 20.8 minutes (Lidocaine)
• 20.8 minutes(control).

There was no difference in the frequency of persistent pain >2 at 90 minutes:

There were no major side effects in any patient, although minor effects such as flushing occurred more often with MgSO4.

Discussion and Will this Change our Practice

This was a randomised, blinded study comparing MgSo4 and Lidocaine to placebo as adjuncts to one particular NSAID( Diclofenac 75 mg IM) for renal colic. 

Rescue analgesia was needed less in the MgSO4 group :

• 17.1% (MgSO4)
• 22.5% (Lidocaine)
• 28.9% (Saline)

More patients in the MgSO4 group reached a 50% reduction in pain 30 minutes following treatment:

• 81.7% (MgSO4)
• 72.9% (Lidocaine)
• 71.8% (Saline)

The predetermined clinically significant point of pain score < 1.3, was however, not different in the 3 groups.

We don't know what effect different dosages of MgSO4 may have had and if the potential side effects would have been too significant to use.

 I think this is a positive study.... perhaps. It demonstrated that rescue analgesia was needed less often in the MgSO4 group and that patients achieved a more rapid decrease in pain with MgSO4, there was no difference between the 3 groups in terms of pre-determined clinical importance (pain <1.3/10).

All three groups had a high pain score at presentation ( all > 8/10). I will usually give antiinflammatories but may give IV narcotic analgesia simultaneously, if the patient is in significant pain and 8.5/10, as was found in this study, is significant pain. 
This study won't change my practice, as I think a small dose of narcotic analgesia works very effectively and I usually won't wait too long to acutely reduce the patient's pain. I may consider using MgSo4, if the patient has allegies to narcotics, or if the pain seems to be refractory to narcotics, although there are also other options, that are probably more effective.