What dose of magnesium sulfate for hypomagnesemia?

Magnesium Replacement for Hypomagnesemia with Level 0.9

For severe hypomagnesemia with a magnesium level of 0.9 mg/dL, administer 2 g (16 mEq) of IV magnesium sulfate over 15-30 minutes, followed by continuous infusion of 1-2 g/hour until levels normalize. 1

Severity Assessment and Initial Management

• A serum magnesium level of 0.9 mg/dL indicates severe hypomagnesemia (<1.2 mg/dL) requiring:
  • Hospital admission for IV replacement therapy 1
  • ECG monitoring during replacement to detect arrhythmias 1
  • Concurrent monitoring of potassium and calcium levels 1

Dosing Protocol

Initial Dose:

• 2 g (16 mEq) IV magnesium sulfate over 15-30 minutes 1
• Must be diluted to concentration of 20% or less prior to administration 2
• Common diluents: 5% Dextrose Injection or 0.9% Sodium Chloride Injection 2

Maintenance Dosing:

• Follow with continuous infusion of 1-2 g/hour for severe cases 1
• Alternative approach: For severe hypomagnesemia, up to 250 mg (approximately 2 mEq) per kg of body weight may be given IM within a four-hour period 2
• Another option: 5 g (approximately 40 mEq) can be added to one liter of IV fluid for slow infusion over three hours 2

Monitoring and Follow-up

• Check serum magnesium 24 hours after completion of IV therapy 1
• Continue ECG monitoring if:
  • Magnesium level drops further
  • Patient is on medications that prolong QT interval 1
• Target serum magnesium level of 6 mg/100 mL is considered optimal for control of seizures if present 2
• Total daily dose should not exceed 30-40 g in 24 hours 2

Special Considerations

• In patients with renal impairment:

  • Maximum dosage is 20 grams/48 hours 2
  • More frequent serum magnesium monitoring required 2
  • Establish adequate renal function before administering magnesium 3

• Monitor for associated electrolyte abnormalities:

  • Hypomagnesemia often coexists with hypokalemia and hypocalcemia 1, 3
  • Correct these concurrently for optimal outcomes

Transition to Oral Therapy

• Once stabilized, transition to oral magnesium supplementation:
  • Typical dosing of 12-24 mmol daily in divided doses 1
  • Continue until magnesium levels normalize

Clinical Pearls and Pitfalls

• Rate of IV injection should generally not exceed 150 mg/minute 2
• Hypomagnesemia increases risk of Torsades de Pointes and ventricular arrhythmias, even with normal magnesium levels 1, 4
• Continuous use of magnesium sulfate in pregnancy beyond 5-7 days can cause fetal abnormalities 2
• Symptoms of hypomagnesemia typically don't appear until levels fall below 1.2 mg/dL 3
• Avoid magnesium in patients with WPW syndrome who are receiving calcium channel blockers or digitalis 1

By following this protocol, you can effectively correct severe hypomagnesemia while monitoring for potential complications and addressing associated electrolyte abnormalities.