From the Guidelines
The workup for hypomagnesemia begins with measuring serum magnesium levels, typically considered deficient when below 1.8 mg/dL, and treatment depends on severity and symptoms, with intravenous magnesium sulfate recommended for severe cases and oral supplementation for moderate or asymptomatic cases 1. The diagnosis of hypomagnesemia involves measuring serum magnesium levels, and additional testing should include serum calcium, potassium, and phosphate levels, as these electrolytes are often affected simultaneously. Evaluation of renal function with BUN and creatinine is important to guide treatment, and a 24-hour urine magnesium collection may help determine if the cause is renal wasting. Some key points to consider in the workup and treatment of hypomagnesemia include:
- Measuring serum magnesium levels to confirm deficiency
- Evaluating renal function to guide treatment
- Correcting concurrent potassium and calcium deficiencies, as magnesium is required for their proper regulation
- Using intravenous magnesium sulfate for severe symptomatic hypomagnesemia, and oral supplementation for moderate or asymptomatic cases
- Monitoring serum levels regularly during treatment to prevent hypermagnesemia, especially in patients with renal impairment Treatment should continue until the underlying cause is addressed, with serum levels monitored every 12-24 hours during IV replacement and weekly during oral therapy. According to the most recent evidence, intravenous magnesium sulfate should be administered at 1-2 grams over 15 minutes, followed by an infusion of 4-8 grams over 24 hours for severe symptomatic hypomagnesemia, and oral supplementation is preferred for moderate or asymptomatic hypomagnesemia, using magnesium oxide, magnesium chloride, or magnesium lactate 1. Patients with renal impairment require careful dosing to prevent hypermagnesemia, while those with severe diarrhea or malabsorption may need higher doses or parenteral administration. It is also important to note that hypomagnesemia can be associated with other electrolyte abnormalities, such as hypokalemia and hypophosphatemia, and that treatment should be tailored to the individual patient's needs 1. In addition, the use of dialysis solutions containing potassium, phosphate, and magnesium can help prevent electrolyte disorders during kidney replacement therapy 1. Overall, the workup and treatment of hypomagnesemia require a comprehensive approach that takes into account the underlying cause, severity, and symptoms, as well as the patient's renal function and other electrolyte levels.
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. Magnesium Sulfate Injection, USP is suitable for replacement therapy in magnesium deficiency, especially in acute hypomagnesemia accompanied by signs of tetany similar to those observed in hypocalcemia.
The workup for hypomagnesemia typically involves:
- Checking serum magnesium levels to confirm the diagnosis
- Evaluating for signs and symptoms of hypomagnesemia, such as tetany, muscle weakness, and cardiac arrhythmias
- Assessing renal function, as magnesium deficiency can be exacerbated by renal insufficiency
The treatment for hypomagnesemia involves:
- Mild magnesium deficiency: 1 g (8.12 mEq) of magnesium sulfate injected IM every 6 hours for 4 doses
- Severe hypomagnesemia: up to 250 mg (2 mEq) per kg of body weight given IM within 4 hours, or 5 g (40 mEq) added to 1 L of 5% Dextrose Injection or 0.9% Sodium Chloride Injection for slow IV infusion over 3 hours 2
- Replacement therapy: magnesium sulfate injection is suitable for replacement therapy in magnesium deficiency, especially in acute hypomagnesemia accompanied by signs of tetany 2
From the Research
Diagnosis of Hypomagnesemia
- Hypomagnesemia is defined as a serum magnesium level less than 1.8 mg/dL (< 0.74 mmol/L) 3
- The first step to determine the likely cause of the hypomagnesemia is to measure fractional excretion of magnesium and urinary calcium-creatinine ratio 3
- Laboratory assessment of body magnesium stores largely relies on the measurement of serum magnesium levels that are a poor proxy for total body stores but does correlate with the development of symptoms 4
Causes of Hypomagnesemia
- Hypomagnesemia may result from inadequate magnesium intake, increased gastrointestinal or renal losses, or redistribution from extracellular to intracellular space 3
- Increased renal magnesium loss can result from genetic or acquired renal disorders 3
- Certain medications such as amphotericin B, aminoglycosides, and cisplatin can cause hypomagnesemia 4
- Proton pump inhibitors (PPIs) are also known to cause hypomagnesemia 5
Treatment of Hypomagnesemia
- Asymptomatic patients should be treated with oral magnesium supplements 3
- Parenteral magnesium should be reserved for symptomatic patients with severe magnesium deficiency (< 1.2 mg/dL) 3
- Intravenous or intramuscular magnesium sulfate should be used when urgent correction of hypomagnesemia is required, such as with myocardial ischemia, post cardiopulmonary bypass, and torsades de pointes 6
- Oral magnesium preparations are available for chronic use 6
Special Considerations
- Patients with advanced diseases are exposed to many causes of hypomagnesaemia, including pharmacological causes 7
- Measuring magnesium levels in the blood of patients with advanced diseases is important to diagnose and treat hypomagnesaemia 7
- Hypomagnesaemia can be alleviated with intravenous or oral magnesium administration 7