What is the appropriate dose of magnesium for a patient with hypomagnesemia in an inpatient setting?

From the FDA Drug Label

DOSAGE & ADMINISTRATION Dosage of magnesium sulfate must be carefully adjusted according to individual requirements and response, and administration of the drug should be discontinued as soon as the desired effect is obtained. In Magnesium Deficiency In the treatment of mild magnesium deficiency, the usual adult dose is 1 g, equivalent to 8. 12 mEq of magnesium (2 mL of the 50% solution) injected IM every six hours for four doses (equivalent to a total of 32.5 mEq of magnesium per 24 hours). For severe hypomagnesemia, as much as 250 mg (approximately 2 mEq) per kg of body weight (0. 5 mL of the 50% solution) may be given IM within a period of four hours if necessary. Alternatively, 5 g (approximately 40 mEq) can be added to one liter of 5% Dextrose Injection, USP or 0. 9% Sodium Chloride Injection, USP for slow IV infusion over a three-hour period.

The appropriate dose of magnesium for a patient with hypomagnesemia in an inpatient setting is:

• For mild magnesium deficiency: 1 g (8.12 mEq) IM every 6 hours for 4 doses (total of 32.5 mEq per 24 hours) 1
• For severe hypomagnesemia:
  • 250 mg (2 mEq) per kg of body weight IM within 4 hours if necessary 1
  • Alternatively, 5 g (40 mEq) IV infusion over 3 hours 1

From the Research

For a patient with hypomagnesemia in an inpatient setting, I recommend administering 2 grams of magnesium sulfate intravenously over 1-2 hours, followed by reassessment of magnesium levels after 4-6 hours, as this approach is supported by the most recent and highest quality study available 2.

Key Considerations

• The initial dose is appropriate for moderate hypomagnesemia (serum Mg 1.0-1.5 mg/dL) and should be adjusted based on the patient's renal function and severity of symptoms.
• If the patient has renal impairment, the dose should be reduced by 50% to avoid hypermagnesemia.
• For patients with severe symptoms like seizures or arrhythmias, consider giving 4 grams IV over 4 hours.
• After the initial correction, maintenance therapy with 1-2 grams IV every 6 hours may be needed until levels normalize (>1.8 mg/dL).

Monitoring and Safety

• Monitor for signs of hypermagnesemia during replacement, including hypotension, respiratory depression, and loss of deep tendon reflexes.
• Magnesium replacement is crucial as hypomagnesemia can cause cardiac arrhythmias, neuromuscular irritability, and can worsen hypokalemia and hypocalcemia since magnesium is essential for proper electrolyte balance and cellular function.

Evidence-Based Decision

The recommendation is based on the study by 2, which found that prolonged magnesium infusion rates did not decrease magnesium replacement requirements, and the most effective approach is to administer the initial dose over 1-2 hours.

Additional Considerations

• The normal reference range for serum magnesium is 0.75 to 0.95 mmol/L (1.82 to 2.31 mg/dL), but values within this range do not rule out deficiencies 3.
• Magnesium deficiency can have serious health consequences, including increased risk of type 2 diabetes and cardiovascular diseases 3.