Magnesium citrate
Magnesium citrate
Generic Name
Magnesium citrate
Mechanism
- Osmotic laxative: Magnesium ions attract water into the intestinal lumen via ion exchange and osmosis.
- Smooth‑muscle relaxation: Magnesium antagonizes calcium‑mediated contraction, promoting colonic motility.
- Citric acid synergy: Enhances intestinal motility by stimulating acid‑activated potassium channels; also prevents precipitation of magnesium in capsules.
The net effect is increased stool water content, accelerated transit, and reduced straining.
Pharmacokinetics
| Parameter | Estimate |
| Absorption | Rapid (within 30 min), ~30–40 % bioavailability. |
| Distribution | Primarily extracellular; low plasma protein binding (~5 %). |
| Metabolism | No significant hepatic metabolism; remains largely unchanged. |
| Elimination | Renally cleared (≈97 % unchanged) via glomerular filtration; half‑life 1–2 h in normal kidneys. |
| Special populations | Reduced clearance in chronic kidney disease (CKD), resulting in ↑ plasma magnesium. |
Indications
- Acute constipation in adults and children (≥ 3 years).
- Pre‑procedural bowel cleansing for colonoscopy, sigmoidoscopy, or MR imaging.
- Short‑term management of magnesium deficiency when oral supplementation is preferred.
Contraindications
- Severe renal impairment (eGFR < 30 mL/min) – risk of hypermagnesemia.
- Acute or chronic heart block – magnesium can depress conduction.
- Pregnancy & lactation: Generally safe; use lowest effective dose for flare‑ups.
- HERPES ZOSTER: Not contraindicated but may increase susceptibility.
Warnings
• Monitor serum magnesium in patients with CKD or those on other magnesium‑containing products.
• Avoid in patients with chronic intestinal malabsorption unless under specialist supervision.
Dosing
| Population | Regimen | Notes |
| Adults (constipation) | 10–20 g (≈1–2 mL of 10 % solution administered orally or rectally) | 1–2 h before first defecation; repeat as needed. |
| Adults (bowel prep) | 45–60 g (≈4–6 mL of 10 % solution 600 mL total) | Usually two doses 1–4 h apart; adequate hydration. |
| Pediatrics (≥3 y) | 0.75 g/kg (max 20 g) | Use flexible‑dose “tinkering” with liquid preparations. |
| Children (short‑term Mg deficiency) | 0.5 g/kg; monitor serum Mg | Adjust per renal function. |
• Use a glass or clear plastic bottle for accurate volume measurement.
• Mix with 20–200 mL of water; let sit 2–5 min before ingestion if formulated as powder.
Adverse Effects
- Common: Diarrhea, cramping, abdominal bloating, nausea.
- Serious:
- Hypermagnesemia (serum Mg > 2.5 mmol/L) → hypotension, bradycardia, respiratory depression.
- Allergic reactions (rare; rash, itching).
- Interference with electrolyte balance (e.g., hypocalcemia).
Monitoring
- Serum magnesium: baseline in CKD or long‑term use; target 1.2–2.0 mmol/L.
- Electrolytes: potassium, calcium, phosphate when high cumulative doses.
- Renal function: creatinine, eGFR every 4–6 weeks with chronic use.
- Vital signs: pulse, blood pressure, respiratory rate in patients at risk for hypomagnesemia.
Clinical Pearls
- Use the lowest effective dose: 10 g of the 10 % solution (1 mL) often suffices for constipation, reducing GI upset.
- Hydration is key: Adequate fluid intake prevents dehydration from osmotic load—instructions for bowel prep should emphasize water ≥ 1.5 L throughout the day.
- Rectal administration: A single dose of 20 mL rectally can provide rapid relief in patients unable to swallow medications.
- For colonoscopies, combine magnesium citrate with a low‑residue diet 24 h prior to reduce aspiration risk.
- Pregnancy safety: Both first and second trimesters are considered safe for short bursts; avoid routine daily use due to potential imbalance of electrolytes.
*All information reflects current data available up to 2026.*