Recommended Dosage of Magnesium Citrate for Constipation
For adults with constipation, the recommended dose of magnesium citrate is 6.5 to 10 fluid ounces (maximum 10 fl oz in 24 hours), which should be taken with a full 8-ounce glass of liquid. 1
Dosing Guidelines by Age
- Adults and children 12+ years: 6.5 to 10 fl oz (maximum 10 fl oz in 24 hours)
- Children 6 to under 12 years: 3 to 7 fl oz (maximum 7 fl oz in 24 hours)
- Children 2 to under 6 years: 2 to 3 fl oz (maximum 3 fl oz in 24 hours)
- Children under 2 years: Consult a doctor
Mechanism of Action
Magnesium citrate works as an osmotic laxative by:
- Retaining fluid in the colon
- Increasing intestinal water content
- Promoting bowel movement through increased intestinal pressure
Administration Instructions
- Shake well before using
- Drink a full glass (8 ounces) of liquid with each dose
- May be taken as a single daily dose or in divided doses
- For best results, ensure adequate hydration before and after taking magnesium citrate
Precautions and Contraindications
- Renal insufficiency: Magnesium citrate is contraindicated in patients with renal insufficiency due to the risk of hypermagnesemia 2, 3
- Monitoring: Watch for signs of hypermagnesemia (muscle weakness, respiratory depression, cardiac abnormalities) in at-risk patients 4
- Pregnancy: Lactulose (15g daily) is the only osmotic agent specifically studied in pregnancy and should be preferred over magnesium preparations 3
Alternative Options for Constipation
If magnesium citrate is not appropriate, consider these alternatives:
First-line option: Polyethylene glycol (PEG) 17g daily - safe in renal insufficiency, no significant systemic absorption, and effective for up to 6 months 2, 3
Fiber supplements: Psyllium at 14g/1,000 kcal intake per day - can be used alone or with PEG, but requires adequate hydration 2, 3
Other osmotic laxatives:
Stimulant laxatives (for short-term use):
Clinical Considerations
- Magnesium citrate is generally well tolerated but can cause abdominal cramping, nausea, and diarrhea
- The efficacy of magnesium-based laxatives is comparable to stimulant laxatives like senna for chronic constipation 5
- Risk of hypermagnesemia increases with prolonged use, especially in patients with decreased renal function 4
- Approximately 15% of orally administered magnesium is absorbed systemically, with the remainder excreted in feces 6
Monitoring
- Assess response to treatment and adjust as needed based on symptom control
- Monitor for electrolyte abnormalities, particularly in patients with renal insufficiency or elderly patients
- Discontinue any non-essential constipating medications when possible
Remember to shake the bottle well before using and ensure adequate hydration when taking magnesium citrate to maximize effectiveness and minimize side effects.