What is the proper protocol for administering a magnesium sulfate drip?

Magnesium Sulfate Drip Administration Protocol

The proper protocol for administering a magnesium sulfate drip depends on the clinical indication, with standard dosing for preeclampsia/eclampsia being a 4-6g loading dose over 20-30 minutes followed by a maintenance infusion of 1-2g/hour, while for severe asthma a 2g dose is given over 20 minutes. 1, 2

Dosing by Clinical Indication

For Preeclampsia/Eclampsia:

• Loading dose: 4-6g IV magnesium sulfate diluted to 20% or less concentration, administered over 20-30 minutes 1, 3
• Maintenance dose: 1-2g/hour continuous infusion via controlled infusion pump 4
  • For overweight patients (BMI ≥25 kg/m²), 2g/hour maintenance is more likely to achieve therapeutic levels than 1g/hour 5, 6
  • For normal weight patients, 1g/hour may be sufficient with fewer side effects 7
• Alternative regimen (Pritchard): After 4g IV loading dose, give 5g IM in each buttock (total 14g loading), then 5g IM every 4 hours in alternating buttocks 1

For Severe Refractory Asthma:

• 2g IV magnesium sulfate diluted to 20% or less concentration, administered over 20 minutes 1, 2
• Not recommended for mild or moderate asthma exacerbations 2

For Torsades de Pointes:

• 2g IV magnesium sulfate as first-line therapy regardless of serum magnesium level 1, 2
• May repeat 2g doses if episodes persist 2

Preparation and Administration

• Magnesium sulfate 50% solution MUST be diluted to 20% or less concentration prior to IV infusion 3
• Use controlled infusion pump for maintenance doses to ensure accurate delivery 4
• Rate of administration should be slow and cautious to avoid hypermagnesemia 3

Monitoring Parameters

• Monitor deep tendon reflexes (patellar reflex) before each dose - if absent, hold dose until reflexes return 3
• Monitor respiratory rate - should remain ≥16 breaths/minute 3
• Maintain urine output at ≥100 mL over 4 hours preceding each dose 3
• Monitor serum magnesium levels:
  • Therapeutic range for eclampsia prevention/treatment: 4.8-8.4 mg/dL (2.5-5 mEq/L) 4, 5
  • Deep tendon reflexes begin to diminish at levels >4 mEq/L 3
  • Reflexes may be absent at 10 mEq/L, where respiratory depression becomes a concern 3

Signs of Magnesium Toxicity

• Loss of patellar reflex: 3.5-5 mmol/L 4
• Respiratory depression: 5-6.5 mmol/L 4
• Altered cardiac conduction: >7.5 mmol/L 4
• Cardiac arrest: >12.5 mmol/L 4

Important Precautions

• Have calcium (calcium chloride or gluconate) immediately available to counteract magnesium toxicity 1, 3
• Use with caution in patients with renal impairment as magnesium is excreted by the kidneys 3
• Adjust dosage in geriatric patients due to potential impaired renal function - should not exceed 20g in 48 hours 3
• Use caution when administering with CNS depressants, neuromuscular blocking agents, or cardiac glycosides due to potential interactions 3

Special Considerations

• For overweight patients, higher maintenance doses (2g/hour) may be needed to achieve therapeutic levels 5, 6
• Despite standard dosing, up to 42% of patients may not achieve target therapeutic levels 8
• Ionized magnesium is the active form but does not correlate well with total magnesium levels 8