Why would a patient take magnesium citrate (twice a day)?

Magnesium Citrate BID: Primary Use for Constipation Management

Magnesium citrate taken twice daily (BID) is primarily prescribed for constipation management, particularly in patients with persistent constipation that has not responded to other treatments. 1

Mechanism and Indications

Magnesium citrate works through two main mechanisms:

• Osmotic effect: Poorly absorbed magnesium ions draw water into the intestinal lumen, increasing stool fluidity and promoting bowel movements 2
• Stimulation of digestive hormones: May trigger release of hormones that enhance intestinal motility 2

Primary indications for BID dosing:

1. Persistent constipation

   • When single daily dosing is insufficient
   • For patients with opioid-induced constipation 1
   • For chronic idiopathic constipation that hasn't responded to other treatments 1

2. Palliative care settings

   • Particularly in cancer patients with months to weeks of life expectancy 1
   • When other laxatives (bisacodyl, senna) have failed to provide relief

Dosing Considerations

• Standard adult dosing: 6.5 to 10 fl oz daily, which may be divided into twice daily administration 3
• Maximum daily dose: 10 fl oz in 24 hours 3
• Timing: Typically administered with a full glass (8 oz) of water with each dose 3

Clinical Decision Algorithm

1. First-line options (try before magnesium citrate):

   • Increase fluids and dietary fiber
   • Stimulant laxatives (senna, bisacodyl)
   • Stool softeners

2. When to consider magnesium citrate BID:

   • When first-line treatments fail
   • For patients with opioid-induced constipation
   • When impaction has been ruled out
   • When obstruction has been excluded

3. Contraindications:

   • Renal insufficiency (risk of hypermagnesemia) 4
   • Congestive heart failure 4
   • Intestinal obstruction

Important Monitoring and Precautions

• Renal function: Monitor in patients on long-term therapy 4
• Electrolytes: Check magnesium levels periodically, especially in elderly patients 4
• Hydration status: Ensure adequate fluid intake to prevent dehydration
• Risk of hypermagnesemia: Can cause serious complications including paralytic ileus in excessive doses 5

Special Considerations

• Palliative care: In patients with limited life expectancy, magnesium citrate is often part of a stepped approach to constipation management 1
• Drug interactions: Use with caution in patients taking medications that may interact with magnesium 4
• Elderly patients: Monitor for hyponatremia and adjust dosing as needed 4

Magnesium citrate BID should be used judiciously and discontinued once regular bowel movements are established, as prolonged use may lead to dependence or electrolyte disturbances.