Name

magnesium sulfate

Class

Electrolyte

CNS depressant

Description/Mechanism

Magnesium sulfate reduces striated muscle contractions and blocks peripheral neuromuscular transmission by reducing acetylcholine release at the myoneural junction. In emergency care, magnesium sulfate is used in the management of seizures associated with toxemia of pregnancy.

Other uses of magnesium sulfate include uterine relaxation (to inhibit contractions of premature labor), as a bronchodilator after beta agonist and anticholinergic agents have been used, replacement therapy for magnesium deficiency, as a cathartic to reduce the absorption of poisons from the GI tract, and in the initial therapy for convulsions. Magnesium sulfate is frequently used as an initial treatment in the management of torsades de pointes, and dyrhythmias secondary to TCA overdose or digitalis toxicity. The drug is also considered as a class IIa agent (probably helpful) for refractory VF/VT after administration of other antidysrhythmics.

Onset

<1 minute

Duration

3-4 hours

Indications

Seizures of eclampsia (toxemia of pregnancy)

Torsades de pointes

Suspected hypomagnesemic state

Refractory VF

Contraindications

Heart Block

Adverse Reactions

Diaphoresis

Facial flushing

Hypotension

Depressed reflexes

Bradycardia

Respiratory depression

Drug Interactions

CNS depressant effects may be enhanced if the patient is taking other CNS depressants.

Serious changes in cardiac function may occur with cardiac glycosides.

Supplied

10%, 12.5%, 50% solution

Dose/Administration

Seizure activity associated with pregnancy

Adult

IV: 1-4 g (8-32 mEq) diluted to 10%, maximum dose of 1.5 ml/min

Torsades de pointes, hypomagnesemia, refractory VF/VT

Adult

IV Infusion: 1-2 g (2-4 ml of a 50% solution) in 10 ml of D5W over 1-2 minutes; administer IV push in cardiac arrest

Pediatric

Not recommended

Special Consideration

Pregnancy Safety: Magnesium sulfate is administered for the treatment of toxemia of pregnancy. It is recommended that the drug not be administered in the 2 hours prior to delivery, if possible.

IV calcium gluconate or calcium chloride should be available as antagonist to magnesium if needed.

Convulsions may occur up to 48 hour after delivery, necessitating continued therapy.

The "cure" for toxemia is usually delivery of the baby.

Magnesium must be used with caution in patients with renal failure, since it is cleared by the kidneys and can reach toxic levels easily in those patients.

Prophylactic administration of magnesium sulfate for patients with AMI should be considered