Dosing and uses of MgSO4 (magnesium sulfate)
Adult dosage forms and strengths
injectable solution
- 40mg/mL
- 80mg/mL
- 50%
infusion solution
- 1g/100mL
- 2g/100mL
Hypomagnesemia
Mild: 1 g IM q6hr for 4 doses
Severe: 5 g IV over 3 hours
Maintenance: 30-60 mg/kg/day IV
Toxemia of Pregnancy
Indicated to prevent seizures associated with pre-eclampsia, and for control of seizures with eclampsia
4-5 g (diluted in 250 mL NS/D5W) IV in combination with either (a) up to 10 g (10 mL of undiluted 50% solution) divided and administered IM into each buttock or (b) after initial IV dose, 1-3 g/hr IV
Torsades de Pointes
With pulse (ACLS): 1-2 g slow IV (diluted in 50-100 mL D5W) over 5-60 minutes, then 0.5-1 g/hr IV
Cardiac arrest (ACLS): 1-2 g slow IV (diluted in 10 mL D5W) over 5-20 minutes
Preterm Labor (Off-label)
Used as a tocolytic to stop preterm labor
Loading dose: 4-6 g IV over 20 minutes; maintenance: 2-4 g/hr IV for 12-24 hours as tolerated after contractions cease
Do not exceed 5-7 days of continuous treatment; longer treatment duration may lead to hypocalcemia in developing fetus resulting in neonates with skeletal abnormalities related to osteopenia
Dosing Modifications
Severe renal impairment: Do not exceed 20 g/48 hr
Pediatric dosage forms and strengths
injectable solution
- 40mg/mL
- 80mg/mL
- 50%
infusion solution
- 1g/100mL
- 2g/100mL
Acute Nephritis
100 mg/kg IM q4-6hr PRN or 20-40 mg/kg IM PRn
Severe: 100-200 mg/kg IV as 1-3% solution; administer total dose within 1 hr, one-half within first 15-20 minutes
Hypomagnesemia
IV/IM: 25-50 mg/kg q4-6hr for 3-4 doses PRn
PO: 100-200 mg/kg q6hr
Bronchospasm (Off-label)
25-50 mg/kg IV over 10-20 minutes
MgSO4 (magnesium sulfate) adverse (side) effects
Frequency not defined
Circulatory collapse
Respiratory paralysis
Hypothermia
Pulmonary edema
Depressed reflexes
Hypotension
Flushing
Drowsiness
Depressed cardiac function
Diaphoresis
Hypocalcemia
Hypophosphatemia
Hyperkalemia
Visual changes
Warnings
Contraindications
Hypersensitivity
Myocardial damage, diabetic coma, heart block
Hypermagnesemia
Hypercalcemia
Administration during 2 hours preceding delivery for mothers with toxemia of pregnancy
Cautions
Fetal skeletal demineralization, hypocalcemia, and hypermagnesemia abnormalities reported with continuous long-term use (ie, longer than 5-7 days) for off-label treatment of preterm labor in pregnant women; the effect on the developing fetus may result in neonates with skeletal abnormalities
In patients with renal impairment, ensure that renal excretory capacity is not exceeded
Use with caution in digitalized patients
Use with extreme caution in patients with myasthenia gravis or other neuromuscular disease
Hypomagnesemia is usually associated with hypokalemia (potassium levels must be normalized)
Monitor renal function, blood pressure, respiratory rate, and deep tendon reflex when magnesium sulfate is administered parenterally
Pregnancy and lactation
Pregnancy category: d
Fetal skeletal demineralization, hypocalcemia, and hypermagnesemia reported with continuous long-term use (ie, longer than 5-7 days) for off-label treatment of preterm labor in pregnant women; the effect on the developing fetus may result in neonates with skeletal abnormalities
Continuous administration of magnesium sulfate injection to treat preterm labor is not approved and that the safety and efficacy of use for this indication are not established
Lactation: Safe
Pregnancy categories
A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.
B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.
C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.
D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.
X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.
NA: Information not available.
Pharmacology of MgSO4 (magnesium sulfate)
Mechanism of action
Depresses CNS, blocks peripheral neuromuscular transmission, produces anticonvulsant effects; decreases amount of acetylcholine released at end-plate by motor nerve impulse
Slows rate of SA node impulse formation in myocardium and prolongs conduction time
Promotes movement of calcium, potassium, and sodium in and out of cells and stabilizes excitable membranes
Promotes osmotic retention of fluid in colon, causing distention and increased peristaltic activity, which subsequently results in bowel evacuation
Absorption
Onset (anticonvulsant): IV, immediate; IM, 1 hr
Duration (anticonvulsant): IV, 30 min; IM, 3-4 hr
Distribution
Protein bound: 30%
Extracellular distribution: 1-2%
Elimination
Excretion: Urine
Administration
IV Incompatibilities
Solution: IV fat emulsion 10%
Additive: Amphotericin B, cyclosporine, dobutamine, polymyxin B sulfate, procaine, sodium bicarbonate
Y-site: Alatrofloxacin, amiodarone (at 500 mg/mL MgSO4; may be compatible at 20 mg/mL), amphotericin B cholesteryl sulfate, cefepime, ciprofloxacin (?)
IV Preparation
Intermittent infusion: Dilute to 60 mg/mL
IV Administration
Infuse over 2-4 hr (hypomagnesemia) or as otherwise specified; rate not to exceed 125 mg/kg/hr
In severe cases, half of the dose may be infused over first 15-20 minutes
Rapid infusions (over 10-20 minutes) may be used for treatment of severe asthma or torsades de pointes ventricular tachycardia
Cautiously infuse diluted solution through patent IV line
IM Administration
Dilute to maximum concentration of 200 mg/mL before injection
