Magnesium Sulfate Poisoning: Symptoms and Treatment
Magnesium sulfate poisoning requires immediate administration of intravenous calcium as the primary treatment, along with supportive care targeting specific symptoms based on serum magnesium levels. 1
Clinical Presentation of Magnesium Toxicity
Cardiovascular Manifestations
- ECG interval changes (prolonged PR, QRS, and QT intervals) occur at magnesium levels of 2.5-5 mmol/L 2
- AV nodal conduction block, bradycardia, hypotension at levels of 6-10 mmol/L 2
- Cardiac arrest can occur at levels exceeding 12.5 mmol/L 3
- Vasodilation and circulatory collapse may develop as toxicity progresses 4
Neurological Manifestations
- Loss of tendon reflexes, sedation, severe muscular weakness, and respiratory depression at levels of 4-5 mmol/L 2
- Deep tendon reflexes begin to diminish when magnesium levels exceed 4 mEq/L 4
- Reflexes may be absent at 10 mEq/L, where respiratory paralysis becomes a potential hazard 4
- Flaccid paralysis and CNS depression may progress to respiratory paralysis 4
Other Symptoms
- Gastrointestinal symptoms: nausea and vomiting 2
- Skin changes: flushing and sweating 2, 4
- Electrolyte/fluid abnormalities: hypophosphatemia, hyperosmolar dehydration 2
- Hypocalcemia with signs of tetany may occur secondary to magnesium toxicity 4
- Hypothermia may develop in severe cases 4
Treatment Protocol
Immediate Interventions
- Administer intravenous calcium as a physiological antagonist to magnesium 1
- Calcium chloride 10% 5-10 mL or calcium gluconate 10% 15-30 mL IV over 2-5 minutes 1
- Do not delay calcium administration while waiting for laboratory confirmation if clinical signs strongly suggest magnesium toxicity 1
Supportive Care
- Continuous cardiac monitoring for arrhythmias 1
- Correct other electrolyte abnormalities, particularly potassium 1
- Blood pressure support with vasopressors if hypotension persists despite calcium administration and fluid resuscitation 1
- Maintain urine output at a level of 100 mL or more during the four hours preceding each dose in cases of ongoing magnesium therapy 4
Monitoring
- Monitor serum magnesium levels and clinical status to avoid consequences of overdosage 4
- Check deep tendon reflexes regularly - their absence indicates potential toxicity 4
- Monitor respiratory rate - approximately 16 breaths or more per minute indicates adequate respiratory function 4
- In patients with renal impairment, more careful monitoring is required as magnesium is exclusively excreted by the kidneys 4
Special Considerations
Patients with Renal Impairment
- Use magnesium with caution in patients with renal impairment 4
- Patients with renal failure can develop toxicity after relatively lower magnesium doses 2
- In patients with severe renal impairment, dosage should not exceed 20 g in 48 hours 4
Pregnant Patients
- Iatrogenic overdose is possible in pregnant women receiving magnesium sulfate for preeclampsia/eclampsia, particularly if the woman becomes oliguric 2
- In pregnant patients with preeclampsia who received therapeutic magnesium sulfate, the same principles of treatment apply, but with careful attention to maternal and fetal monitoring 1
Common Pitfalls to Avoid
- Delaying calcium administration while waiting for laboratory confirmation when clinical signs strongly suggest magnesium toxicity 1
- Failing to monitor deep tendon reflexes, which are an early clinical indicator of toxicity 4
- Overlooking renal function, as impaired kidney function significantly increases the risk of toxicity 4
- Continuing magnesium administration when oliguria develops, especially in pregnant women 2