Hypermagnesaemia—elevated magnesium levels in the blood—is an uncommon but potentially serious condition that requires prompt recognition and appropriate management. Whilst the body typically regulates magnesium effectively through renal excretion, excess accumulation can occur when kidney function is impaired or when magnesium-containing medications and supplements are overused. Understanding how to remove excess magnesium from the body is essential for patients with chronic kidney disease, those taking magnesium supplements, and healthcare professionals managing electrolyte disturbances. This article explores the medical treatments available to eliminate excess magnesium, when to seek urgent help, and practical prevention strategies aligned with NHS and NICE guidance.

Understanding Excess Magnesium in the Body

Hypermagnesaemia, or elevated magnesium levels in the blood, is a relatively uncommon condition that occurs when serum magnesium concentrations exceed the normal range of 0.7–1.0 mmol/L. Unlike magnesium deficiency, which is more frequently encountered in clinical practice, excess magnesium typically develops only under specific circumstances and rarely occurs from dietary intake alone in individuals with normal kidney function.

The kidneys play a crucial role in maintaining magnesium homeostasis by efficiently excreting excess magnesium through urine. In healthy individuals, the renal system effectively regulates magnesium balance, preventing accumulation even with higher dietary intake. However, when kidney function is impaired—particularly in chronic kidney disease (CKD) stages 4–5 with an estimated glomerular filtration rate (eGFR) below 30 mL/min/1.73m²—this protective mechanism becomes compromised, significantly increasing the risk of hypermagnesaemia.

Excess magnesium most commonly results from excessive supplementation, particularly in individuals with reduced renal function, or from overuse of magnesium-containing medications such as antacids (e.g., magnesium hydroxide), laxatives (e.g., magnesium sulphate), or enemas. Iatrogenic causes include overzealous intravenous magnesium administration during treatment of eclampsia or cardiac arrhythmias. Less commonly, conditions causing increased magnesium release from tissues—such as rhabdomyolysis, tumour lysis syndrome, or severe burns—may contribute to elevated levels, typically when renal function is also compromised.

Understanding the underlying cause of hypermagnesaemia is essential for appropriate management. Whilst mild elevations may be asymptomatic and resolve with simple interventions, significant hypermagnesaemia (>3.5 mmol/L) constitutes a medical emergency requiring urgent treatment to prevent potentially life-threatening complications affecting the cardiovascular and neuromuscular systems.

Symptoms of High Magnesium Levels (Hypermagnesaemia)

The clinical manifestations of hypermagnesaemia are directly related to serum magnesium concentrations and typically become apparent when levels exceed 1.5 mmol/L. Mild hypermagnesaemia (just above the reference range up to ~2.0 mmol/L) may be entirely asymptomatic or produce subtle symptoms that are easily overlooked, including nausea, vomiting, facial flushing, and generalised weakness. Patients may also experience a sensation of warmth, mild lethargy, or reduced appetite during this stage.

As magnesium levels rise to moderate elevations (2.0–3.5 mmol/L), neuromuscular symptoms become more pronounced. Hyporeflexia—diminished or absent deep tendon reflexes—is a characteristic finding and often one of the earliest objective signs detected on clinical examination. Patients may develop muscle weakness affecting both proximal and distal muscle groups, leading to difficulty with mobility and fine motor tasks. Drowsiness, confusion, and slurred speech may emerge as magnesium begins to affect the central nervous system. Gastrointestinal motility is also impaired, potentially causing constipation or ileus.

Severe hypermagnesaemia (>3.5 mmol/L) poses significant risks to cardiovascular and respiratory function. Cardiac manifestations include bradycardia, hypotension, and electrocardiographic changes such as prolonged PR interval, widened QRS complex, and progression to heart block. At extremely high concentrations (>5.0 mmol/L), complete heart block, cardiac arrest, and respiratory paralysis may occur due to magnesium's calcium-antagonist effects on cardiac conduction and neuromuscular transmission.

Respiratory depression represents another critical complication, as elevated magnesium impairs the function of respiratory muscles and central respiratory drive. Patients may exhibit shallow breathing, reduced respiratory rate, and in severe cases, respiratory failure requiring mechanical ventilation. Immediate medical intervention is essential when these severe symptoms develop.

Medical Treatments to Remove Excess Magnesium

The management of hypermagnesaemia depends on the severity of elevation, presence of symptoms, and underlying renal function. The first and most important step is immediate discontinuation of all magnesium-containing products, including supplements, antacids, laxatives, and intravenous magnesium infusions. A thorough medication review should be conducted to identify and eliminate all potential sources.

For patients with mild, asymptomatic hypermagnesaemia and preserved kidney function, conservative management is often sufficient. Intravenous fluid administration with normal saline (0.9% sodium chloride) promotes renal magnesium excretion by increasing glomerular filtration and reducing tubular reabsorption. This approach is particularly effective in individuals with adequate renal function (eGFR >60 mL/min/1.73m²). Fluid resuscitation should be administered cautiously, with careful monitoring of fluid balance to avoid volume overload, particularly in elderly patients or those with cardiac conditions.

Loop diuretics may be administered alongside intravenous fluids to enhance magnesium elimination through increased diuresis. This combination therapy increases urinary magnesium excretion and is typically reserved for symptomatic patients or those with moderately elevated levels. Close monitoring of electrolytes—particularly potassium and calcium—is essential, as loop diuretics promote loss of multiple cations. The specific dosing should be determined by clinicians based on individual patient factors.

In cases of severe, symptomatic hypermagnesaemia, particularly when accompanied by cardiac conduction abnormalities or neuromuscular compromise, intravenous calcium gluconate (10 mL of 10% solution administered slowly over approximately 10 minutes with ECG monitoring) serves as a direct antagonist to magnesium's effects. Calcium temporarily reverses the cardiac and neuromuscular toxicity by competing with magnesium at cellular receptor sites, providing a critical bridge whilst definitive elimination strategies are implemented. This intervention does not lower magnesium levels but mitigates life-threatening manifestations.

Haemodialysis represents the most effective method for rapidly removing excess magnesium and is indicated for patients with severe, symptomatic hypermagnesaemia not responding to conservative measures, or when significant renal impairment precludes adequate spontaneous excretion. This decision requires urgent nephrology consultation. Dialysis using low-magnesium or magnesium-free dialysate can reduce serum levels significantly within a 3–4 hour session and is life-saving in cases of magnesium toxicity with haemodynamic instability or respiratory failure.

When to Seek Medical Help for High Magnesium

Recognising when to seek medical attention for suspected hypermagnesaemia is crucial for preventing serious complications. Immediate emergency assessment (via 999 or attendance at A&E) is warranted if you or someone in your care experiences severe symptoms including profound muscle weakness preventing movement, difficulty breathing or shortness of breath, significantly slowed heart rate or irregular heartbeat, severe confusion or loss of consciousness, or inability to stay awake.

Patients with known risk factors for hypermagnesaemia should maintain heightened awareness and seek medical review if concerning symptoms develop. This includes individuals with chronic kidney disease (particularly stages 4–5), those taking regular magnesium supplements exceeding 400 mg daily, people using magnesium-containing laxatives or antacids frequently, and patients receiving intravenous magnesium therapy. If you have CKD and develop nausea, unusual weakness, or drowsiness whilst taking magnesium-containing products, contact your GP or renal team promptly for assessment and possible blood tests.

Magnesium levels are not routinely monitored in all CKD patients but may be checked if you are symptomatic, taking magnesium-containing medicines, or when clinically indicated. Those prescribed magnesium supplementation for conditions such as pre-eclampsia, cardiac arrhythmias, or chronic constipation should undergo periodic review to ensure appropriate dosing and absence of accumulation.

If you experience persistent mild symptoms such as ongoing nausea, reduced reflexes noticed by yourself or others, unexplained constipation, or generalised weakness whilst taking magnesium-containing products, arrange a non-urgent GP appointment within 1–2 weeks. Your GP can arrange blood tests to measure serum magnesium, assess renal function, and review your medication regimen. Do not abruptly stop prescribed medications without medical advice, but do discontinue over-the-counter magnesium supplements if you suspect they may be contributing to symptoms.

Preventing Magnesium Overload

Prevention of hypermagnesaemia centres on appropriate use of magnesium-containing products and awareness of individual risk factors. For the general population with normal kidney function, dietary magnesium from food sources—including green leafy vegetables, nuts, seeds, whole grains, and legumes—poses virtually no risk of toxicity, as the gastrointestinal tract limits absorption and healthy kidneys efficiently excrete excess amounts. The NHS recommends 300 mg daily for men and 270 mg daily for women, amounts easily achieved through a balanced diet without supplementation.

Magnesium supplementation should be approached cautiously and ideally under medical supervision. Over-the-counter supplements vary widely in elemental magnesium content, with common forms including magnesium oxide (60% elemental magnesium), magnesium citrate (16%), and magnesium glycinate (14%). The NHS recommended upper limit for supplemental magnesium is 400 mg daily for adults, though individuals with impaired renal function should use significantly lower doses or avoid supplementation entirely unless specifically prescribed. Always inform your GP and pharmacist about all supplements you take, as they may interact with prescribed medications or contribute to electrolyte imbalances.

Patients with chronic kidney disease require particular vigilance. The BNF and product information for magnesium-containing medicines emphasise avoiding magnesium-containing antacids and laxatives in individuals with eGFR <30 mL/min/1.73m². Alternative treatments for constipation (such as macrogols or lactulose) and dyspepsia (such as alginates or proton pump inhibitors) should be preferentially used. If you have CKD, always check medication labels for magnesium content and consult your pharmacist before purchasing over-the-counter remedies for heartburn, indigestion, or constipation.

Healthcare professionals prescribing or administering intravenous magnesium should adhere to local protocols, verify renal function before administration, use appropriate dosing regimens, and monitor serum levels during prolonged therapy. Patient education is essential—ensure individuals understand the signs of magnesium toxicity and know when to seek help. Regular medication reviews, particularly for elderly patients or those with multiple comorbidities, help identify unnecessary magnesium-containing products that can be safely discontinued, reducing the cumulative burden and risk of hypermagnesaemia.

If you suspect an adverse reaction to a magnesium-containing medicine or supplement, report it to the MHRA Yellow Card scheme.

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