From the FDA Drug Label
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 rate of magnesium sulfate (MgSO4) drip for treating hypomagnesemia is:
- Slow IV infusion: 5 g (approximately 40 mEq) over a three-hour period, which is equivalent to approximately 1.33 g/hour or 13.3 mg/minute 1. The absorption of magnesium sulfate is:
- IM administration: therapeutic plasma levels are reached in 60 minutes 1.
- IV administration: therapeutic levels are reached almost immediately 1.
From the Research
For hypomagnesemia, magnesium sulfate can be administered intravenously at a rate of 1-2 grams per hour for severe deficiency, with a typical regimen involving giving 1-2 grams of magnesium sulfate diluted in 50-100 mL of D5W or normal saline over 15-30 minutes for acute symptomatic hypomagnesemia, followed by a maintenance infusion of 0.5-1 gram per hour for 24 hours, as supported by the most recent study 2.
Key Considerations
- The incidence of hypomagnesemia in critically ill patients is around 27.27% 2.
- Intravenous administration of 1 g of MgSO4 results in a rise of serum magnesium levels by 0.1 mg/dL in patients with normal eGFR and around 0.15 mg/dL in patients with eGFR values between 30 and 89 mL/min/1.73 m2 2.
- Absorption of IV magnesium is immediate as it bypasses the gastrointestinal tract, with approximately 50-70% being excreted in urine while the remainder is distributed to tissues.
- Serum magnesium levels should be monitored every 6 hours during replacement therapy, with a target level of 2.0-2.5 mg/dL.
- Patients should be monitored for signs of hypermagnesemia including hypotension, flushing, and loss of deep tendon reflexes.
- Caution is needed in patients with renal impairment as reduced excretion can lead to magnesium toxicity, as noted in studies 3, 4, 2.
Administration and Monitoring
- For less severe cases, 1-2 grams can be given over 1-2 hours.
- The rapid correction of magnesium deficiency is important because hypomagnesemia can cause cardiac arrhythmias, neuromuscular irritability, and can make hypokalemia and hypocalcemia refractory to treatment.
- Continuous magnesium infusions may be an effective option for managing systemic anti-cancer therapy-related hypomagnesemia, as shown in a study 5.
- Subcutaneous magnesium administration may be a feasible option for long-term management in ambulatory patients, as described in a case report 6.