What are the signs of hypermagnesemia (elevated magnesium levels) in the body?

Signs of Hypermagnesemia (Too Much Magnesium)

Hypermagnesemia (serum magnesium >2.2 mEq/L) produces a progressive spectrum of neurological, cardiovascular, and gastrointestinal symptoms that can be life-threatening, with the most critical signs being muscular weakness, cardiac conduction abnormalities, respiratory depression, and altered mental status. 1

Neurological Manifestations

The nervous system is particularly sensitive to elevated magnesium levels:

• Muscular weakness and flaccid paralysis develop as magnesium interferes with neuromuscular transmission 1, 2
• Drowsiness, confusion, and depressed level of consciousness progressing to coma occur with severe elevations 1, 2
• Ataxia (loss of coordination) may be present 1
• Dysautonomia (autonomic nervous system dysfunction) can develop 2
• Loss of deep tendon reflexes typically occurs before respiratory depression 3

Cardiovascular Signs

Cardiac manifestations follow a predictable progression as magnesium levels rise:

• Vasodilation and hypotension occur even at moderately elevated levels 1
• ECG changes include prolonged PR interval, prolonged QRS duration, and prolonged QT interval at magnesium levels of 2.5-5 mmol/L 1
• Bradycardia develops as conduction slows 1
• Atrioventricular nodal conduction block occurs at severely elevated levels (6-10 mmol/L) 1
• Cardiac arrhythmias and ultimately cardiac arrest can occur at extreme elevations 1

Respiratory Manifestations

• Hypoventilation develops as respiratory muscles weaken 1
• Respiratory muscle paralysis can lead to respiratory failure requiring mechanical ventilation 2
• Cardiorespiratory arrest may occur at extremely high levels 1

Gastrointestinal Signs

• Paralytic ileus (intestinal smooth muscle dysfunction) manifests as vomiting, obstipation, and abdominal distension 4
• This complication is underrecognized but can occur even with mild renal insufficiency 4

Clinical Severity Thresholds

The American Heart Association provides specific magnesium level correlations with clinical findings 1:

• 2.5-5 mmol/L: ECG changes (prolonged PR, QRS, QT intervals)
• 6-10 mmol/L: Atrioventricular block, bradycardia, hypotension, cardiac arrest risk

High-Risk Populations

Renal dysfunction is the primary risk factor, as the kidneys are responsible for magnesium excretion 1, 3:

• Patients with chronic kidney disease or acute kidney injury 3, 5
• Patients receiving magnesium-containing medications (antacids, laxatives like milk of magnesia, magnesium citrate, Epsom salts) 5, 4
• Pregnant women receiving magnesium for preterm labor (iatrogenic overdose) 1
• Patients with normal renal function can still develop hypermagnesemia with excessive magnesium intake 5, 4

Critical Clinical Pitfall

Hypermagnesemia is often overlooked due to its relative rarity and unfamiliarity among clinicians 3, 5. The condition can be fatal if not promptly recognized, particularly in patients taking over-the-counter magnesium-containing preparations for constipation 5. Regular monitoring of serum magnesium is essential in at-risk populations, especially those with any degree of renal impairment 3, 5.