Does a slower rate of intravenous (IV) magnesium infusion improve absorption?

IV Magnesium Infusion Rate and Absorption

Slower rates of IV magnesium infusion do not improve absorption or retention compared to more rapid infusion rates. Recent evidence consistently shows no benefit to prolonged infusion times for magnesium repletion 1, 2, 3.

Evidence Summary

Absorption and Retention

• Multiple studies have directly compared prolonged versus rapid infusion rates:
  • A 2020 study in hospitalized general medicine patients found no difference in magnesium replacement requirements between prolonged (0.5 g/hr) and short infusion rates (>0.5 g/hr, median 1.8 g/hr) 1
  • A 2024 oncology study demonstrated no statistically significant difference in magnesium requirements between prolonged and rapid infusion rates (2.18g vs 2.15g per outpatient visit) 2
  • A 2018 study in hematopoietic cell transplant patients showed no difference in total magnesium replacement (22.5g vs 21.4g) or days requiring IV replacement (7.2 vs 6.2 days) between slow and rapid infusion groups 3

Clinical Implications

• Regardless of infusion rate, IV magnesium levels typically fall below 2.0 mg/dL within 24 hours of administration 4
• For 2g doses (most common), less than half of patients maintain magnesium levels above 2.0 mg/dL just 12 hours after administration 4
• Rapid infusion rates can significantly reduce chair time (by approximately 110 minutes per outpatient encounter) without compromising therapeutic outcomes 2

Practical Administration Guidelines

Standard Dosing and Administration

• For severe hypomagnesemia: 1-2g IV over 15-30 minutes for urgent correction 5
• For severe refractory asthma: 25-50 mg/kg (maximum: 2g) over 15-30 minutes 6
• For torsades de pointes: 1-2g IV (bolus for pulseless torsades, over 10-20 minutes for torsades with pulses) 6
• For severe refractory asthma: 2g administered over 20 minutes 6

Safety Considerations

• Monitor for potential side effects during infusion:
  • Hypotension and bradycardia with rapid infusion 6
  • Flushing and light-headedness 6
• Have calcium chloride available to reverse potential magnesium toxicity if needed 6
• Monitor for infusion reactions, particularly with faster rates 6

Clinical Decision Making

When to Choose Rapid vs. Slower Infusion

• Rapid infusion (15-30 minutes) is appropriate for:

  • Most routine magnesium repletion cases
  • Situations where chair time or IV access is limited
  • Outpatient settings where efficiency is important

• Consider slower infusion (over 60 minutes) only for:

  • Patients with known sensitivity to rapid infusion
  • Patients with compromised cardiovascular status who may not tolerate rapid fluid shifts

Common Pitfalls

• Unnecessarily prolonging infusion time based on the incorrect assumption that it improves retention
• Failing to monitor for hypotension during rapid infusion
• Underestimating the frequency of required dosing (most patients need at least twice-daily dosing to maintain levels >2.0 mg/dL) 4

In conclusion, the evidence does not support the practice of prolonging magnesium infusion rates to improve absorption or retention. Healthcare providers can safely administer IV magnesium at more rapid rates (15-30 minutes for standard doses) without compromising therapeutic efficacy, while improving workflow efficiency and patient convenience.