Class: CNS depressant

Description

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 to manage seizures associated with toxemia of pregnancy. Other uses 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 Gl tract, and in the initial therapy for convulsions. Magnesium sulfate is gaining popularity as an initial treatment in the management of various dysrhythmias, particularly torsades de pointes, and dysrhythmias secondary to a tricyclic antidepressant overdose or digitalis toxicity. The drug is also considered as a class Ila agent (probably helpful) for refractory ventricular fibrillation and ventricular tachycardia after administration of lidocaine or bretylium doses.

Onset & Duration

Onset: Immediate

Duration: 3-4 hr

Indications

Seizures of eclampsia (toxemia of pregnancy)

Torsades de pointes

Contraindications

Heart block

Adverse Reactions

Diaphoresis Facial flushing Hypotension

Depressed reflexes Hypothermia

Reduced heart rate Circulatory collapse

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.

How Supplied

5 and 10 ml of a 10% solution in prefilled syringe

Dosage and Administration

seizure activity associated with pregnancy

Adult: 1-4 g (8-32 mEq); maximum dose of 1.5 ml/min

Pediatric: NA

For magnesium deficiency related to cardiac dysrhythmias, torsades de pointes, or

refractory ventricular fibrillation:

Adult: 1-2 g diluted in 100 ml of D5W administered over 1-2 minutes

Pediatric: Not recommended

Special Considerations

Pregnancy safety: Magnesium sulfate is administered to treat toxemia of pregnancy. It is recommended that the drug not be administered in the 2 hours before delivery, if possible. IV calcium gluconate or calcium chloride should be available as an antagonist to magnesium if needed.

Convulsions may occur up to 48 hr after delivery, necessitating continued therapy. The "cure" for toxemia is 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 acute mvocardial infarction should be considered.