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Generic Name: magnesium sulfate
Brand and Other Names: MgSO4
Drug Class: Antidysrhythmics, V; Electrolytes
What is magnesium sulfate, and what is it used for?
Magnesium sulfate is a salt of magnesium, a naturally occurring mineral that is important for normal functioning of many systems in the body, particularly nerves and muscles. Magnesium sulfate is administered to prevent and treat convulsions (seizures) from preeclampsia and eclampsia (toxemia) in pregnant women. Toxemia in pregnancy is a condition with high blood pressure and damage to organs such as liver or kidney.
Magnesium sulfate is also used to treat certain heart rhythm disorders, magnesium deficiency, and acute kidney inflammation (nephritis) in children. Magnesium sulfate works in the following ways:
- Prevents convulsions by depressing the central nervous system and blocking the transmission of nerve signals to the muscles to make them contract
- Reduces the release of acetylcholine, a chemical that nerve cells secrete to make muscles contract
- Lowers the heart rate by slowing down the electrical impulse formation in the heart and prolongation of the conduction time
- Improves kidney function by facilitating normal movement of calcium, potassium, and sodium in and out of cells and stabilizing excitable cell membranes
Magnesium sulfate is used in the treatment of following conditions:
Adult
- Hypomagnesemia (low magnesium levels in blood)
- Toxemia of pregnancy (preeclampsia and eclampsia)
- Torsades de pointes (a type of life-threatening abnormality in heart rhythm)
- Preterm labor (off-label)
Pediatric
- Acute nephritis
- Hypomagnesemia
- Bronchospasm (off-label)
Warnings
- Do not administer magnesium sulfate to patients who:
- Are hypersensitive to magnesium sulfate or any of its components
- Have myocardial damage or heart block
- Are in a diabetic coma
- Have high magnesium levels (hypermagnesemia)
- Have high calcium levels (hypercalcemia)
- Do not administer magnesium sulfate during 2 hours preceding delivery in mothers with toxemia of pregnancy
- In patients with kidney impairment, ensure that renal excretory capacity is not exceeded
- Use with caution in patients treated with digitalis (digoxin), a drug used to treat heart failure and abnormal heart rhythms
- Use with extreme caution in patients with myasthenia gravis or other neuromuscular diseases
- Hypomagnesemia is usually associated with drop in potassium levels (hypokalemia)
- Monitor kidney function, blood pressure, respiratory rate, and deep tendon reflex when magnesium sulfate is administered intravenously (parenterally)
What are the side effects of magnesium sulfate?
Side effects of magnesium sulfate, which are usually the result of magnesium sulfate intoxication, include:
- Flushing (warmth, redness, or tingly feeling)
- Increased sweating
- Low blood pressure (hypotension)
- Depressed/poor reflexes
- Flaccid paralysis
- Low core body temperature (hypothermia)
- Circulatory collapse
- Depressed cardiac function
- Central nervous system (CNS) depression
- Respiratory paralysis
- Excess fluid in the lungs (pulmonary edema)
- Extreme drowsiness
- Low blood calcium (hypocalcemia)
- Low blood phosphates (hypophosphatemia)
- Low blood potassium (hyperkalemia)
- Visual changes
- Headache
- Breathing difficulties
- Muscle tightness or contraction
- Weakness
- Feeling faint
- Cold feeling
- Confusion
- Anxiety
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.
What are the dosages of magnesium sulfate?
Injectable solution
- 40mg/mL
- 80mg/mL
Infusion solution
- 1g/100mL
- 2g/100mL
Adult
Hypomagnesemia
- Mild: 1 g intramuscularly (IM) every 6 hours for 4 doses
- Severe: 5 g intravenously (IV) over 3 hours
- Maintenance: 30-60 mg/kg/day IV
Toxemia of Pregnancy
- Indicated to prevent seizures associated with pre-eclampsia, and for control of seizures with eclampsia
- 4-5 g (diluted in 250 mL NS/D5W) intravenously (IV) in combination with either (a) up to 10 g (10 mL of undiluted 50% solution) divided and administered intramuscularly (IM) into each buttock or (b) after initial IV dose, 1-3 g/ hour IV
Torsades de Pointes
- With pulse (advanced cardiac life support – ACLS): 1-2 g slow intravenous (IV) (diluted in 50-100 mL D5W) over 5-60 minutes, then 0.5-1 g/ hour IV
- Cardiac arrest (ACLS): 1-2 g slow IV (diluted in 10 mL D5W) over 5-20 minutes
Preterm Labor (Off-label)
Used as a labor suppressant (tocolytic) to stop preterm labor
- Loading dose: 4-6 g intravenously (IV) over 20 minutes; maintenance: 2-4 g/hour IV for 12-24 hours as tolerated after contractions cease
- Do not exceed 5-7 days of continuous treatment; longer treatment duration may lead to low blood calcium (hypocalcemia) in developing fetuses resulting in neonates with skeletal abnormalities related to osteopenia
Dosing Modifications
- Severe renal impairment: Do not exceed 20 g/48 hours
Pediatric
Acute Nephritis
- 100 mg/kg intramuscularly (IM) every 4-6 hours as needed or 20-40 mg/kg IM as needed
- Severe: 100-200 mg/kg intravenously (IV) as 1-3% solution; administer total dose within 1 hour, one-half within first 15-20 minutes
Hypomagnesemia
- Intravenous/intramuscular (IV/IM): 25-50 mg/kg every 4-6 hours for 3-4 doses as needed
- Oral: 100-200 mg/kg every 6 hours
Bronchospasm (Off-label)
- 25-50 mg/kg intravenously (IV) over 10-20 minutes
Overdose
- Symptoms of magnesium overdose include a sharp drop in blood pressure and respiratory paralysis
- Onset of magnesium intoxication may be detected by the disappearance of kneecap (patellar) reflex
- Treatment of magnesium overdose often requires artificial ventilation, and intravenous calcium is used to counteract the effects of excess magnesium (hypermagnesemia)
- Hypermagnesemia in the newborn may require resuscitation, assisted ventilation and intravenous calcium
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What drugs interact with magnesium sulfate?
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.
Magnesium sulfate has no known severe interactions with other drugs.
- Serious interactions of magnesium sulfate include:
- demeclocycline
- doxycycline
- eltrombopag
- lymecycline
- minocycline
- oxytetracycline
- tetracycline
- Magnesium sulfate has moderate interactions with at least 24 different drugs.
- Magnesium sulfate has mild interactions with at least 43 different drugs.
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 of 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 health care provider if you have any questions about the medication.
Pregnancy and breastfeeding
- Use magnesium sulfate during pregnancy only in life-threatening emergencies when no safer drug is available.
- Magnesium sulfate can cause fetal abnormalities when used for longer than 5-7 days in pregnant women.
- Abnormalities such as fetal skeletal mineral loss, low blood calcium (hypocalcemia), and high blood magnesium (hypermagnesemia) are reported with continuous long-term use (more than 5-7 days) for off-label treatment of preterm labor in pregnant women; the effect on the developing fetus may result in skeletal abnormalities in newborns.
- Magnesium sulfate administered by continuous IV infusion (especially for longer than 24 hours preceding delivery) in toxemic women to control convulsions may cause magnesium toxicity in the newborn.
- The safety and efficacy of use for delaying preterm labor are not established, continuous administration of magnesium sulfate injection to treat preterm labor is not approved.
- Magnesium sulfate is present in milk with use of intravenous (parenteral) magnesium sulfate and should be used with caution in nursing mothers.
