What is the workup for a magnesium 10,000mg (Over-The-Counter) overdose?

Management of Magnesium 10,000mg OTC Overdose

The management of a magnesium 10,000mg overdose requires immediate assessment of vital signs, ECG monitoring, evaluation of neurological status, and administration of intravenous calcium as the primary antidote. 1

Clinical Manifestations of Magnesium Toxicity

• Mild-moderate toxicity (serum levels 2.5-5 mmol/L) presents with nausea, flushing, headache, lethargy, diminished deep tendon reflexes, and ECG changes including prolonged PR, QRS, and QT intervals 2
• Severe toxicity (serum levels 6-10 mmol/L) manifests as AV nodal conduction block, bradycardia, hypotension, and cardiac arrest 2, 1
• Neurological effects include loss of tendon reflexes, sedation, severe muscular weakness, and respiratory depression at levels of 4-5 mmol/L 2
• Other signs include gastrointestinal symptoms (nausea and vomiting), skin changes (flushing), and electrolyte abnormalities (hypophosphatemia) 2

Initial Assessment

• Obtain vital signs including blood pressure, heart rate, respiratory rate, and oxygen saturation 1
• Perform 12-lead ECG to assess for cardiac conduction abnormalities 1
• Check deep tendon reflexes and neurological status 1
• Obtain laboratory studies including serum magnesium, potassium, calcium, phosphate, and creatinine levels 1
• Assess renal function, as patients with renal impairment are at higher risk for magnesium toxicity even with lower doses 1, 3

Management Algorithm

Step 1: Stabilization

• Secure airway, breathing, and circulation as needed 2
• Provide supplemental oxygen if respiratory depression is present 1
• Establish IV access for fluid administration and medication 1

Step 2: Antidote Administration

• Administer intravenous calcium as a physiological antagonist to magnesium's effects 1, 4
  • Calcium chloride 10% 5-10mL (500-1000mg) or calcium gluconate 10% 15-30mL (1.5-3g) IV 1
  • May repeat based on clinical response 4

Step 3: Enhanced Elimination

• Initiate aggressive IV fluid therapy to promote renal excretion of magnesium 5
• Consider hemodialysis for patients with:
  • Severe symptoms unresponsive to calcium and supportive care 5
  • Renal impairment limiting magnesium excretion 1, 5
  • Extremely high magnesium levels (>8-10 mmol/L) 5, 6

Step 4: Additional Interventions for Severe Toxicity

• For cardiac arrest: follow standard ACLS protocols with emphasis on calcium administration 2
• For respiratory depression: consider mechanical ventilation 7
• For refractory cases: forced diuresis and dextrose-insulin infusion may be considered 7

Monitoring and Follow-up

• Continuous cardiac monitoring until symptoms resolve 1
• Serial magnesium levels until trending downward 1
• Monitor calcium levels, especially after calcium administration 1
• Assess renal function to guide management and follow-up 1, 3
• Contact Poison Control Center for complicated cases (1-800-222-1222) 1

Special Considerations

• Patients with normal renal function typically recover well with supportive care and calcium administration 6
• Mortality is associated with serum magnesium levels exceeding 8 mmol/L without intervention 6
• Iatrogenic overdoses have been reported to cause cardiac arrest but can be successfully managed with prompt intervention 8, 4
• Be vigilant about medication errors, particularly regarding units of measurement for magnesium preparations 8