SGEM#489: Smooth Muscle Relaxator – But does Magnesium Work for Renal Colic?

Date: October 10, 2025 Guest Skeptic: Dr. Sergey Motov is an Emergency Physician in the Department of Emergency Medicine, Maimonides Medical Center in New York City. He is also one of the world’s leading researchers on pain management in the emergency department.  Case: A 37-year-old man presents to the emergency department (ED) with severe right-sided flank pain.  The pain started about eight hours ago as a vague discomfort in his right flank, but it has gotten progressively worse and now is radiating to his groin. Patient reports nausea, an increased urge to urinate and noticing blood in his urine on one occasion. The patient denies prior medical or surgical history. Upon ED arrival, his vital signs are normal. Physical examination revealed a stated age patient in distress due to severe right flank pain, prominent right-sided costovertebral angle tenderness, and absence of abdominal tenderness or guarding. While strongly considering renal colic in differential diagnosis and reaching for the bedside ultrasound, you are wondering if a single dose of a non-steroidal anti-inflammatory (NSAID) will be enough to relieve this patient’s pain, or should you add Magnesium or Lidocaine? Background: Renal colic is a common and extremely painful emergency department (ED) complaint encountered in the ED that frequently recurs. The nonsteroidal anti-inflammatory drugs (NSAIDs) given intravenously or intramuscularly (IM) are frequently used as first-line therapy. However, about 30% of ED patients receiving NSAIDS require rescue analgesia in the form of opioids. Opioid use, though effective, is limited at times due to the potentially dangerous adverse effects. Thus, there might be a role for other non-opioid classes of drugs to be co-administered with NSAIDs for relief of renal colic. Magnesium sulfate (MgSO₄) has been suggested as a possible treatment option. It may blunt ureteral smooth muscle spasm by antagonizing calcium influx in smooth muscle and by N‑methyl‑D‑aspartate (NMDA) receptor antagonism. These are mechanisms that can reduce visceral pain and augment other analgesics. Small ED trials and meta‑analyses suggest MgSO₄ can reduce pain scores and opioid use in renal colic, though the evidence base has been limited and heterogeneous [1]. Another suggested treatment modality for renal colic is intravenous lidocaine. We looked at this treatment on SGEM#202 and were unimpressed with the efficacy. Systemic lidocaine blocks voltage‑gated sodium channels and appears to modulate central sensitization and visceral pain pathways. In ED populations, systematic reviews indicate IV lidocaine offers variable analgesia with a mixed signal for benefit, and renal colic–specific RCTs suggest it may be inferior to ketorolac and best considered (if at all) as part of a multimodal strategy rather than as monotherapy [2]. Clinical Question: In adult ED patients with suspected renal colic receiving IM diclofenac, does adding IV magnesium sulfate or IV lidocaine increase the proportion achieving ≥50% reduction in pain at 30 minutes compared to a saline placebo? Reference: Toumia M, Sassi S, Dhaoui R, et al. Magnesium Sulfate Versus Lidocaine as an Adjunct for Renal Colic in the Emergency Department: A Randomized, Double-Blind Controlled Trial. Ann Emerg Med 2024 Population: The study enrolled adults aged 18 to 65 years with suspected acute renal colic and a pain score of 5 or more on a 10-point numerical rating scale (NRS). Exclusions: Pregnancy/breastfeeding; NSAID, MgSO₄, or lidocaine contraindication or allergy; renal/hepatic dysfunction; analgesic use in prior 6 h; bleeding diathesis or GI hemorrhage; significant CAD/arrhythmia; seizures; peritoneal signs; altered mental status; anticoagulation; hemodynamic instability; morphine allergy. Intervention: All patients received 75 mg IM diclofenac. The intervention groups then received either 1g IV MgSO₄ (10 mL) over 2-4 minutes or 1.