What intravenous magnesium sulfate dose and infusion schedule should be used in an adult with aluminum‑phosphide (Celphos) poisoning who develops cardiac instability or refractory hypotension, and what are the pediatric dosing recommendations?

Magnesium Sulfate Dosing in Aluminum Phosphide (Celphos) Poisoning

For adults with aluminum phosphide poisoning and cardiac instability or refractory hypotension, administer intravenous magnesium sulfate 1-2 g (8.1-16.2 mEq) as an initial bolus over 2-5 minutes, followed by continuous infusion to maintain serum magnesium >2.0 mmol/L. 1

Adult Dosing Protocol

Initial Bolus Dose

• Administer 1-2 g magnesium sulfate IV push (diluted in 10 mL D5W) for cardiac arrest, torsades de pointes, or polymorphic ventricular tachycardia with QT prolongation 2, 1
• This translates to 8.1-16.2 mEq or 4.05-8.1 mmol of magnesium 3
• Infuse over 2-5 minutes for acute cardiotoxicity 2

Continuous Infusion Regimen

The most effective dosing schedule based on clinical research involves aggressive magnesium replacement 3, 4:

• Initial loading phase: 1 g magnesium sulfate IV bolus, then 1 g every hour for 3 consecutive hours 3
• Maintenance phase: 1 g every 6 hours for the next 24 hours 3
• Total first 24 hours: 30 mmol (approximately 7 g) 3
• Subsequent days: 16 mmol (4 g) daily until recovery or maximum 5 days 3

This higher-dose schedule (dose schedule No. 2) significantly reduced mortality compared to lower-dose regimens in aluminum phosphide poisoning 4. The aggressive dosing maintains magnesium levels persistently above normal, which correlates with improved survival 4.

Target Serum Levels

• Maintain serum magnesium ≥2.0 mmol/L throughout treatment 1
• Maintain serum potassium ≥4.0 mmol/L concurrently, as hypokalemia potentiates arrhythmias 1
• Monitor magnesium levels every 6 hours during the first 24 hours 3

Pediatric Dosing

For children with aluminum phosphide poisoning and cardiac arrest or severe cardiotoxicity:

• Initial bolus: 25-50 mg/kg IV/IO (maximum 2 g) over 10-20 minutes 2
• Alternatively, use the "rule of 6" for continuous infusion: 0.6 × body weight (kg) = mg of magnesium diluted to 100 mL saline; then 1 mL/h delivers 0.1 mcg/kg/min 2

Critical Safety Monitoring

Magnesium Toxicity Recognition

Patients with renal failure require dose reduction and intensive monitoring, as they can develop life-threatening magnesium toxicity at standard doses 1:

• Early signs: Flushing, sweating, hypotension 1
• Severe toxicity: AV block, bradycardia, respiratory paralysis, cardiac arrest 1
• Monitor deep tendon reflexes (loss indicates impending toxicity)
• Check renal function before initiating high-dose protocols

Immediate Reversal Agent

Keep calcium gluconate 10% (15-30 mL) or calcium chloride 10% (5-10 mL) at bedside for immediate IV administration if magnesium toxicity develops 2, 1. Calcium directly antagonizes magnesium's cardiac effects and can be life-saving 2.

Refractory Cases: Escalation Strategy

If cardiac arrhythmias persist despite adequate magnesium replacement 1:

1. Increase heart rate with temporary transvenous pacing or isoproterenol infusion to suppress torsades de pointes 1
2. Consider VA-ECMO for refractory cardiogenic shock or cardiac arrest unresponsive to maximal medical therapy including magnesium 2, 1

Mechanistic Rationale

Aluminum phosphide causes profound hypomagnesemia, which is consistently observed in poisoned patients and correlates with mortality 3, 4. The released phosphine gas inhibits cytochrome c oxidase, causing cellular hypoxia and myocardial dysfunction 5. Magnesium stabilizes cardiac membranes, reduces arrhythmias, and improves outcomes when serum levels are maintained above normal 4. Studies demonstrate mortality reduction from 52% without magnesium to significantly lower rates with aggressive magnesium replacement 3, 4.

Common Pitfalls to Avoid

• Do not use low-dose magnesium protocols (e.g., single 1-2 g bolus only) in aluminum phosphide poisoning, as they fail to maintain therapeutic levels and do not reduce mortality 4
• Do not delay magnesium administration while waiting for laboratory confirmation of hypomagnesemia, as levels drop rapidly and early treatment improves survival 3
• Do not administer magnesium as sole therapy—aggressive supportive care including fluid resuscitation, vasopressors, and sodium bicarbonate for metabolic acidosis remains essential 5, 6
• Avoid routine magnesium in undifferentiated cardiac arrest without evidence of aluminum phosphide poisoning or torsades de pointes, as it provides no benefit 2