3 Indications Where Magnesium Sulfate Should Be Administered Faster Than Normal

MARCH 28, 2016
Pharmacists are the last line of defense in preventing prescribing errors from reaching patients.
 
While many drugs carry a risk of harm to patients, few drugs are more potentially hazardous as electrolytes, and magnesium is no exception.
 
Under most circumstances, the maximum infusion rate of the sulfate salt is 1 g per 60 minutes in asymptomatic patients. However, there are a few situations in which the rate of administration needs to be much faster to take advantage of magnesium’s effects.

  1. Torsades de pointes: Magnesium sulfate 1 to 2 g in 10mL of 5% dextrose in water (D5W) over 5 to 20 minutes
Torsades is a feared rhythm caused by numerous medications or hereditary mutations in the potassium rectifier channels in the heart.
 
While the mainstay of treatment is direct current cardioversion, rapid administration of magnesium decreases the influx of calcium into cardiac cells, lowering the amplitude and suppressing early after depolarizations.

  1. Pulseless ventricular tachycardia: Magnesium sulfate 1 to 2 g in 10mL of D5W over 1 to 2 minutes
In the event of cardiac arrest, where the rhythm is a pulseless ventricular tachycardia, magnesium may be considered. The effects of magnesium may be due to several mechanisms, including improved potassium transport through myocardial potassium channels and shortening of the action potential duration.
 
The key, again, is rapid administration, since time is of the essence in any resuscitation effort.

  1. Eclampsia: Magnesium sulfate 4 to 6 g in a 10% or 20% solution over 3 to 4 minutes
Magnesium sulfate is the drug of choice for treating eclampsia and can be used as prophylaxis against it, as well. Magnesium can reduce the risk of eclampsia by more than 50%, and it may in fact reduce maternal death.

In order to achieve these effects, large doses are often required. These doses are generally well tolerated with flushing as a common adverse event, but absence of deep tendon (commonly patellar) reflexes are a warning signs of looming serious effects of respiratory depression and hypotension.
 


Craig Cocchio, PharmD
Craig Cocchio, PharmD
Craig Cocchio, PharmD, BCPS, is an Emergency Medicine Clinical Pharmacist at Trinity Mother Frances Hospital in Tyler, Texas. Follow on Twitter @iEMPharmD and on his blog at empharmd.blogspot.com
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