Maximum Dose of Magnesium Citrate

The maximum dose of magnesium citrate for adults is 10 fluid ounces (300 mL) in a 24-hour period, as specified by FDA labeling. 1

Dosing Guidelines by Age

Adults and children 12 years and older: 6.5 to 10 fluid ounces, with a maximum of 10 fluid ounces in 24 hours 1
Children 6 to under 12 years: 3 to 7 fluid ounces, with a maximum of 7 fluid ounces in 24 hours 1
Children 2 to under 6 years: 2 to 3 fluid ounces, with a maximum of 3 fluid ounces in 24 hours 1
Children under 2 years: Consult a physician 1

Magnesium citrate creates an osmotic gradient in the gastrointestinal tract that draws water into the intestines, making it particularly effective for constipation 2
For bowel preparation before colonoscopy, magnesium citrate has been used at doses of 300 mL × 3 (900 mL total) divided throughout the preparation period 3
In diabetic patients undergoing colonoscopy, additional doses of magnesium citrate (beyond standard preparation) have shown improved bowel cleansing results (70% vs 54% good preparation) 3
For patients with spinal cord injury, magnesium citrate (20 oz or approximately 600 mL) has been used as part of extended bowel preparation regimens 3

Contraindications: Magnesium citrate is contraindicated in patients with:
- Congestive heart failure 3
- Hypermagnesemia 3
- Severe renal impairment (creatinine clearance <20 mL/min) 2
Electrolyte concerns:
- In patients with normal renal function, serum magnesium imbalances are typically transient and of little clinical concern 3
- Hyponatremia has been observed in patients 65 years and older using magnesium citrate preparations 3
- Magnesium citrate was associated with a higher risk of hospitalization with hyponatremia (absolute risk increase: 0.05%) 3

Shake well before using 1
Drink a full glass (8 ounces) of liquid with each dose 1
May be taken as a single daily dose or in divided doses 1
For optimal effect in constipation management, administer with adequate fluid intake 3
For bowel preparation, magnesium citrate is often more effective when given as part of a split-dose regimen 3

Magnesium citrate has shown superior efficacy compared to PEG-ELS preparations of volumes less than 4L 3
When used for bowel preparation, magnesium citrate has been associated with less vomiting than PEG-ELS but more dizziness 3
The addition of magnesium citrate to enema preparations has been shown to improve bowel preparation quality for flexible sigmoidoscopy 4
For patients with recurrent calcium oxalate nephrolithiasis, magnesium citrate should be administered with meals to maximize urinary citrate increases and minimize urinary calcium increases 5

Monitor for dehydration, especially in elderly patients or those with comorbidities 6
Be aware that magnesium supplementation in doses above the current tolerable upper intake level (350 mg/day) may be safe for most adults, but caution is still warranted with higher therapeutic doses used for bowel preparation 7
When using magnesium citrate for bowel preparation, ensure patients have adequate fluid intake to prevent dehydration 3