Citric acid with magnesium carbonate

How it works

The reaction forms magnesium citrate, an osmotically-active saline laxative that draws water into the bowel lumen to produce evacuation and cleansing of the colon.

Prescribing in practice

• Bowel-cleansing solutions can cause clinically important fluid and electrolyte shifts and dehydration, so use with particular caution in frail or elderly patients and those with cardiac or renal impairment, ensuring adequate hydration.
• It is contraindicated in gastrointestinal obstruction, ileus, gastric retention, toxic colitis or megacolon.
• Magnesium accumulation is a risk in significant renal impairment, so avoid or use only with great care in this group.

Monitoring

Ensure adequate hydration during preparation and consider checking renal function and electrolytes in patients at risk of fluid or electrolyte disturbance.

Counselling the patient

• Follow the timing and dietary instructions exactly so the bowel is properly cleared for your procedure.
• Drink plenty of clear fluids during the preparation to avoid dehydration.
• Expect frequent watery bowel motions and stay near a toilet once you start.

Evidence & guidelines

Endoscopy and prescribing guidance recommend adequate hydration and caution with osmotic bowel-cleansing agents in older and comorbid patients to limit electrolyte and fluid disturbance.