Magnesium Sulfate

• Magnesium Sulfate

• MgSO4

Classification:

• Electrolyte

Mechanism of Action:

• Reduces acetylcholine release at the myoneural junction and inhibits Ca2+ influx through dihydropyridine sensitive voltage dependent channels. This results in reduced striated muscle contractions, blocked peripheral neuromuscular transmission, and relaxation of the vascular smooth muscle.

Indications:

• Torsades de pointes
• Cardiac arrest due to hypomagnesemia
• Eclampsia
• TCA OD with prolonged QTc
• Severe asthma

Contraindications:

•  AV heart blocks, hypocalcemia

Precautions:

• Patients with/taking: Impaired renal function, Myasthenia Gravis, digoxin, shock state, myocardial damage

Adverse Effects:

• Hypotension
• Heart block
• Drowsiness
• Respiratory depression
• Arrhythmia
• Flushing (not harmful; self-resolves)

Dose:

• Cardiac arrest (torsades de pointes or hypomagnesemia): 2 g IVP
• Torsades de pointes (with a pulse): 2 g in 100 mL NS IV over 5 mins
• Severe Asthma: 1-2 g in 100 mL NS IV over 5 mins
• TCA OD with prolonged QTc: 1-2 g in 100 mL NS IV over 20 mins
• Eclampsia: 4 g in 100 mL NS IV over 20 mins

• Cardiac arrest (torsades de pointes or hypomagnesia): 50 mg/kg IVP  (max dose 2 g)
• Torsades de pointes (with a pulse): 50 mg/kg in 100 mL NS IV over 10 mins (max dose 2 g)
• Severe Asthma: 25-50 mg/kg in 100 mL NS IV over 15 mins (max dose 2 g)
• TCA OD with prolonged QTc: 25 mg/kg in 50 mL NS IV over 20 mins (max dose 1 g)

•  May be given IV/IO

• 2 g in 10 mL (20%) vial

• Unless patient is in cardiac arrest, appropriate dose of magnesium sulfate should be injected into 100 mL normal saline bag and administered over period of time as indicated in dosage section.
• If a pregnant patient in the third trimester is complaining of severe headache and/or increased blood pressure (i.e., signs of pre-eclampsia), consider possible treatment options.
• Calcium chloride should be readily available as an antidote for magnesium sulfate in case of respiratory depression (decreased diaphragm neuromuscular action); 1 g over 3 minutes for adults; 10 mg/kg (maximum of 1 g) over 15 minutes for pediatrics.
• Magnesium sulfate is not effective in the setting of COPD.
• Pregnancy category A [the drug is safe to use in pregnant women] 

• Compendium of Pharmaceuticals and Specialties (CPS)