Magnesium Sulfate
Class
Electrolyte, 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 GI
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 IIa 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
1. Seizures of eclampsia (toxicity of pregnancy)
2. Torsades de pointes
3. Hypomagnesium
Contraindications
Heart block, renal disease, hypermagnesium
Adverse Reactions
1. CNS depression
2. Diaphoresis
3. Facial flushing
4. Hypotension
5. Depressed reflexes
6. Hypothermia
7. Reduced heart rate, cardiac arrest, asystole
8. Circulatory collapse
9. Respiratory depression
10. Diarrhea
Drug Interactions
1. CNS depressant effects may be enhanced if the patient is taking other CNS
depressants.
2. Serious changes in cardiac function may occur with cardiac glycosides.
Special Considerations
1. 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.
2. Convulsions may occur up to 48 hr after delivery, necessitating continued
therapy. The “cure” for toxemia is delivery of the baby.
3. 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.
4. Prophylactic administration of magnesium sulfate for patients with acute
myocardial infarction should be considered.
5. Use with caution with renal failure.
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