What are the guidelines for magnesium supplementation?

Magnesium Supplementation Guidelines

Magnesium supplementation should be tailored to specific clinical conditions, with oral organic magnesium salts generally preferred for better bioavailability, while avoiding supplementation in patients with renal insufficiency due to risk of hypermagnesemia. 1, 2

Indications for Magnesium Supplementation

Chronic Idiopathic Constipation

• Magnesium oxide is conditionally recommended for adults with chronic idiopathic constipation (CIC) who have failed other therapies 2
• Start at a lower dose and increase if necessary based on response 2
• Avoid use in patients with renal insufficiency due to risk of hypermagnesemia 2
• Clinical trials for magnesium in CIC were conducted for 4 weeks, though longer-term use is likely appropriate 2

Short Bowel Syndrome

• Patients with short bowel syndrome, particularly those with jejunostomy, experience significant magnesium losses requiring supplementation 2, 1
• Rehydration to correct secondary hyperaldosteronism is the crucial first step before supplementation 2
• Magnesium oxide is commonly given as gelatine 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, 1
• If oral supplements don't normalize levels, oral 1-alpha hydroxy-cholecalciferol (0.25-9.00 μg daily) may improve magnesium balance, but requires monitoring of serum calcium 2
• Intravenous or subcutaneous magnesium may be necessary when oral supplementation is ineffective 2

Erythromelalgia

• Magnesium supplementation may be beneficial in erythromelalgia patients 2
• Start at the recommended daily allowance (350 mg daily for women; 420 mg daily for men) 2
• Increase gradually according to tolerance due to potential side effects 2
• Liquid or dissolvable magnesium products are usually better tolerated than pills 2
• Intravenous administration (2g infused over 2 hours every 2-3 weeks) may be considered, though evidence is limited 2

Severe Magnesium Deficiency

• For mild deficiency: 1g (8.12 mEq) injected IM every six hours for four doses 3
• For severe hypomagnesemia: up to 250 mg/kg body weight IM within four hours 3
• Alternatively, 5g (40 mEq) can be added to 1L of IV fluid for slow infusion over three hours 3
• IV injection rate should generally not exceed 150 mg/minute 3
• Solutions for IV infusion must be diluted to 20% or less concentration prior to administration 3

Dosage Forms and Administration

Oral Supplementation

• Organic magnesium salts (aspartate, citrate, lactate) have better bioavailability than magnesium oxide or hydroxide 1
• Divided doses throughout the day help maintain stable levels 1
• Liquid or dissolvable forms are generally better tolerated than pills 2
• The current tolerable upper intake level (UL) for supplemental magnesium is 350 mg/day, though recent evidence suggests higher doses may be safe 4

Parenteral Administration

• For IV administration, solutions must be diluted to 20% or less concentration 3
• Common diluents include 5% Dextrose Injection and 0.9% Sodium Chloride Injection 3
• Deep IM injection of undiluted (50%) solution is appropriate for adults, but should be diluted to 20% or less for children 3
• IV injection rate should not exceed 150 mg/minute except in severe eclampsia with seizures 3

Monitoring and Precautions

• Regular monitoring of magnesium levels is essential, especially in patients with renal disease 1
• Serum magnesium levels do not accurately reflect total body magnesium status (less than 1% of magnesium is found in blood) 1, 5
• Common side effects include diarrhea, abdominal distension, and gastrointestinal intolerance 2, 4
• Avoid use in patients with renal insufficiency due to risk of hypermagnesemia 2, 3
• Continuous use of magnesium sulfate in pregnancy beyond 5-7 days can cause fetal abnormalities 3

Special Considerations

• Maintain a calcium/magnesium ratio close to 2 in dietary intake 6
• Food sources of magnesium include green leafy vegetables, nuts, legumes, and whole grains 7
• Magnesium deficiency has been associated with various conditions including hypertension, cardiac arrhythmias, diabetes, osteoporosis, migraines, and insomnia 5, 8
• Despite observational data showing associations between low magnesium and cardiovascular disease, major trials of supplementation have reported inconsistent benefits 8
• There is currently no firm recommendation for routine magnesium supplementation except when hypomagnesemia has been proven or suspected as a cause for cardiac arrhythmias 8