magnesium sulfate (antidote)

• Magnesium sulfate is used as an antidote to reverse toxicity caused by digitalis. Digitalis is a chemical found in plants such as foxgloves, which is used to produce digoxin, a drug used to treat irregular heart rhythms (cardiac arrhythmia) and congestive heart failure. Digitalis toxicity causes arrhythmia and magnesium works as an antidote by stabilizing the heartbeat. Magnesium is also used to treat torsades de pointes, a life-threatening heart rhythm disorder that results from low blood magnesium levels (hypomagnesemia).
• Magnesium sulfate is a salt of magnesium, a naturally occurring mineral that is important for the normal functioning of many systems in the body, including nerve function, electrical conduction in the heart, protein synthesis, bone formation and blood pressure regulation. Magnesium sulfate (antidote) is administered as an intravenous injection or infusion.
• Magnesium lowers the heart rate by slowing down the electrical impulse formation in the sinoatrial (SA) node, the natural pacemaker of the heart, and prolongation of the conduction time. Magnesium also facilitates normal movement of calcium, potassium, and sodium in and out of cells and stabilizes excitable cell membranes. These actions help correct the arrhythmia caused by digitalis toxicity or hypomagnesemia.
• Intravenous magnesium may also be administered to correct electrolyte imbalance that can be caused by systemic poisoning from hydrofluoric acid exposure, along with calcium and potassium.

• Do not administer magnesium (antidote) in patients with the following conditions:
  • Hypersensitivity to magnesium sulfate or any of its components
  • Heart muscle (myocardial) damage or heart block
  • Diabetic coma
  • High magnesium levels (hypermagnesemia)
• Magnesium levels of patients receiving magnesium should be continuously monitored to prevent magnesium overdose and toxicity which can cause life-threatening respiratory depression and low blood pressure (hypotension). 
• Injectable calcium salt should be readily available to counteract magnesium toxicity, in the event of overdosage.
• Use with extreme caution in patients with myasthenia gravis or other neuromuscular diseases, magnesium can precipitate a life-threatening myasthenic crisis. If myasthenic crisis is suspected, discontinue magnesium sulfate, secure patient’s airway, provide ventilatory support if required, and institute appropriate intensive care.
• Use with caution in patients with kidney impairment. Magnesium antidote injection solution contains aluminum that can reach toxic concentrations with prolonged intravenous administration to patients with impaired kidney function.
• Use with caution in patients with diabetes mellitus, magnesium antidote is administered in dextrose solution which can increase blood glucose levels.
• Avoid administration of magnesium sulfate with unapproved labor-delaying (tocolytic) drugs such as terbutaline or nifedipine in pregnant women with preterm labor. Serious adverse events such as pulmonary edema and hypotension can result.

Common side effects of magnesium (antidote) include:

• Central nervous system (CNS) depression
• Motor and respiratory paralysis
• Abnormal ECG
• Heart block
• Flushing
• Low core body temperature (hypothermia)
• Low blood pressure (hypotension)
• Diarrhea
• Prolonged bleeding time

Call your doctor immediately if you experience any of the following symptoms or serious side effects while using this drug:

• Serious heart symptoms include fast or pounding heartbeats, fluttering in your chest, shortness of breath, and sudden dizziness;
• Severe headache, confusion, slurred speech, severe weakness, vomiting, loss of coordination, feeling unsteady;
• Severe nervous system reaction with very stiff muscles, high fever, sweating, confusion, fast or uneven heartbeats, tremors, and feeling like you might pass out; or
• Serious eye symptoms include blurred vision, tunnel vision, eye pain or swelling, or seeing halos around lights.

This is not a complete list of all side effects or adverse reactions that may occur from the use of this drug. Call your doctor for medical advice about serious side effects or adverse reactions. You may also report side effects or health problems to the FDA at 1-800-FDA-1088.

IV infusion, premixed in dextrose 5% in water (D5W)

• 10 mg/mL
• 20 mg/mL

IV infusion, premixed in water

• 40 mg/mL
• 80 mg/mL

Injection for dilution

• 500 mg/mL

Adult:

Digitalis Toxicity

• 1-2 g intravenous push (IVP) administration over 5 minutes, then 1 g/hour drip (if Digibind not available)
• Monitor levels every 2 hours; therapeutic goal is 4.5 mEq/L

Other Indications and Uses

• Hydrofluoric acid burns

Pediatric:

Hypomagnesemia or Torsades de Pointes

• Indicated for the treatment of documented hypomagnesemia or for torsades de pointes (polymorphic VT associated with long QT interval)
• There is insufficient evidence to recommend for or against the routine administration of magnesium during cardiac arrest
• 25-50 mg/kg intravenous/intraosseous (IV/IO) over 10-20 minutes (may infuse faster in torsades de pointes); not to exceed 2 g/dose

Overdose

• Magnesium, when used as an antidote, is administered under clinical conditions and is unlikely to result in an overdose, because the patient’s magnesium levels are monitored.
• Symptoms of magnesium overdose include the absence of kneecap reflex, a sharp drop in blood pressure, and respiratory paralysis.
• Overdose may be treated with discontinuation of magnesium, artificial ventilation, and administration of intravenous calcium to counteract the effects of excess magnesium.

Inform your doctor of all medications you are currently taking, who can advise you on any possible drug interactions. Never begin taking, suddenly discontinue, or change the dosage of any medication without your doctor’s recommendation.

• Interactions with the following drugs or drug classes can cause drug-induced renal loss of magnesium:
  • aminoglycosides
  • amphotericin B
  • cyclosporine
  • diuretics
  • digitalis
  • cisplatin
  • alcohol

The drug interactions listed above are not all of the possible interactions or adverse effects. For more information on drug interactions, visit the RxList Drug Interaction Checker.

It is important to always tell your doctor, pharmacist, or health care provider about all prescription and over-the-counter medications you use, as well as the dosage for each, and keep a list of the information. Check with your doctor or healthcare provider if you have any questions about the medication.

• Magnesium (antidote) may be used during pregnancy only if clearly needed.
• Continuous administration of magnesium sulfate for longer than 5-7 days in pregnant women can result in low blood calcium (hypocalcemia), bone mineral loss, bone abnormalities, and low bone density (osteopenia) in the fetus.
• Magnesium administered to pregnant women may cause magnesium toxicity in the newborn with symptoms that may include reduced reflexes (hyporeflexia), low muscle tone (hypotonia), and respiratory depression.
• Magnesium sulfate in 5% dextrose injection is approved for use in pregnant women for the prevention of eclampsia in women with preeclampsia and treatment of seizures and prevention of recurrent seizures in women with eclampsia.
• Continuous administration of magnesium sulfate injection is not approved to treat preterm labor.
• Magnesium is present in breastmilk and IV administration of magnesium should be used with caution in nursing mothers.