Initial Dosage of Magnesium Supplementation
For mild magnesium deficiency, the recommended initial dose is 1 g (equivalent to 8.12 mEq) of magnesium sulfate injected intramuscularly every six hours for four doses. 1
Dosing by Route of Administration and Severity
Intravenous (IV) Administration
- For mild magnesium deficiency: 1 g IV (8.12 mEq) 1
- For severe hypomagnesemia: 5 g (approximately 40 mEq) added to one liter of 5% Dextrose or 0.9% Sodium Chloride for slow IV infusion over a three-hour period 1
- IV injection rate should generally not exceed 150 mg/minute (1.5 mL of a 10% concentration) 1
- Solutions for IV infusion must be diluted to a concentration of 20% or less prior to administration 1
Intramuscular (IM) Administration
- For mild deficiency: 1 g IM every six hours for four doses (equivalent to 32.5 mEq per 24 hours) 1
- For severe hypomagnesemia: Up to 250 mg (approximately 2 mEq) per kg of body weight may be given IM within a four-hour period 1
- Deep IM injection of undiluted (50%) solution is appropriate for adults, but should be diluted to 20% or less for children 1
Oral Administration
- For general health maintenance: Start with the Recommended Dietary Allowance (RDA) of 320 mg/day for women and 420 mg/day for men 2
- For chronic idiopathic constipation: Start with magnesium oxide 400-500 mg daily and titrate based on response 2
- For patients with short bowel syndrome: Magnesium oxide is commonly given as gelatin capsules of 4 mmol (160 mg) to a total of 12-24 mmol daily 2
- Administration at night is preferred when intestinal transit is slowest to improve absorption 2
Special Clinical Scenarios
Asthma and Cardiac Conditions
- For refractory status asthmaticus: 25-50 mg/kg IV (maximum: 2 g) over 15-30 minutes 3
- For torsades de pointes: 25-50 mg/kg IV (maximum: 2 g) as bolus for pulseless torsades, or over 10-20 minutes for torsades with pulses 3
- For patients at risk of ventricular arrhythmias: 2 g IV magnesium sulfate at least twice daily to maintain total serum magnesium above 2 mg/dL 4
Erythromelalgia
- Start at the recommended daily allowance (350 mg daily for women; 420 mg daily for men) 3
- Increase gradually according to tolerance, with doses of 600-6500 mg daily reported as effective in some patients 3
- Liquid or dissolvable magnesium products are usually better tolerated than pills 3
- Intravenous administration (2g infused over 2 hours every 2-3 weeks) may be considered, though evidence is limited 3
Formulation Considerations
- Organic magnesium compounds (aspartate, citrate, lactate, threonate) have better bioavailability than inorganic compounds like magnesium oxide 5
- Liquid or dissolvable forms are generally better tolerated than pills 2
- Dividing high doses of daily administered magnesium compounds does not significantly increase tissue magnesium levels 5
Monitoring and Precautions
- Carefully adjust dosage according to individual requirements and response 1
- Discontinue administration as soon as the desired effect is obtained 1
- Monitor for signs of magnesium toxicity, including hypotension, bradycardia, and respiratory depression 3
- Have calcium chloride available to reverse magnesium toxicity if needed 3
- Avoid magnesium supplementation in patients with renal insufficiency due to risk of hypermagnesemia 2
- For patients on continuous renal replacement therapy, using dialysis solutions containing magnesium can help prevent hypomagnesemia 2
Therapeutic Targets
- A serum magnesium level of 6 mg/100 mL is considered optimal for control of seizures 1
- For general deficiency, aim for serum magnesium concentration >0.85 mmol/L (2.06 mg/dL) 6
- A combination of dietary intake <250 mg/day, urinary excretion <80 mg/day, and serum magnesium <0.85 mmol/L may indicate need for supplementation 6
The choice of magnesium formulation and dosage should be guided by the severity of deficiency, route of administration, and specific clinical condition being treated. Monitoring response and adjusting treatment accordingly is essential for optimal outcomes.