Magnesium Citrate Dosing for Severe Constipation
For adults with severe constipation, the recommended dose of magnesium citrate is 6.5 to 10 fluid ounces (195-300 ml) as a single dose, with a maximum of 10 fluid ounces in 24 hours. 1
Dosing Guidelines by Age Group
- Adults and children ≥12 years: 6.5-10 fl oz (195-300 ml), maximum 10 fl oz in 24 hours
- Children 6 to <12 years: 3-7 fl oz (90-210 ml), maximum 7 fl oz in 24 hours
- Children 2 to <6 years: 2-3 fl oz (60-90 ml), maximum 3 fl oz in 24 hours
- Children <2 years: Consult a doctor 1
Administration Instructions
- Shake well before using
- Drink a full glass (8 ounces) of water with each dose
- May be taken as a single daily dose or in divided doses 1
- For optimal effect, ensure adequate hydration before and after administration
Mechanism of Action
Magnesium citrate works through two primary mechanisms:
- Acts as an osmotic laxative by retaining fluids in the colon
- Creates an osmotic gradient in the GI tract, leading to net secretion of water and electrolytes 2, 3
Efficacy
Magnesium-based laxatives have demonstrated effectiveness for constipation:
- Magnesium oxide at 1.5 g/day significantly increases complete spontaneous bowel movements (CSBMs) compared to placebo (MD 4.29,95% CI 2.93-5.65) 2
- Magnesium-based products show higher response rates (68.3%) compared to placebo (11.7%) 4
- The National Comprehensive Cancer Network recommends magnesium citrate as an option for opioid-induced constipation 2
Precautions and Contraindications
- Renal impairment: Avoid in patients with creatinine clearance <20 mg/dL due to risk of hypermagnesemia 2, 5, 6
- Electrolyte disturbances: Monitor for electrolyte abnormalities, particularly in elderly patients
- Dehydration: Ensure adequate hydration to prevent worsening of dehydration 5
- Bowel obstruction: Rule out obstruction before administration 2, 5
Alternative Options for Special Populations
- Patients with renal insufficiency: Polyethylene glycol (PEG) is the preferred first-line treatment (17g daily) 5
- Pregnant patients: Lactulose (15g daily) is the preferred osmotic laxative 5
- Elderly patients: PEG (17g daily) is particularly effective with fewer side effects 5
Practical Considerations
- For severe constipation, use the higher end of the dosing range (closer to 10 fl oz for adults)
- If using for bowel preparation before procedures, follow specific protocol timing
- Magnesium citrate typically produces a bowel movement within 30 minutes to 6 hours after administration
- For opioid-induced constipation, consider combining with stimulant laxatives like senna 2
Monitoring
- Assess response to treatment
- Monitor for signs of hypermagnesemia (hypotension, nausea, facial flushing, respiratory depression) in at-risk patients
- Discontinue any non-essential constipating medications 5
Magnesium citrate is generally well-tolerated and effective for severe constipation when used appropriately, but careful consideration of patient factors, particularly renal function, is essential for safe administration.