The MedMal Room: Magnesium Sulfate - A Deadly But Effective Medication on Labor & Delivery

The Responsibility Clause - A proven treatment to protect the preterm brain and prevents the mother from having seizures with preeclampsia — but still not FDA-approved for neuroprotection of the baby

Magnesium sulfate is one of obstetrics’ most paradoxical drugs. It can save lives—and it has taken them. It is called a “high-alert medication” because mothers have died from it. It is given for two entirely different reasons, something rare in medicine. The first is to prevent or treat seizures in women with preeclampsia or eclampsia, a use that is FDA-approved. The second is to protect the premature baby’s brain, a use that is not. The same clear fluid dripping into an IV line can mean safety for the mother or protection for the fetus. Yet, both uses carry real risk if not managed precisely.

The Two Indications

1. Seizure Prophylaxis in Preeclampsia and Eclampsia (FDA-Approved)
For generations, magnesium sulfate has been the drug of choice for preeclampsia and eclampsia. It prevents seizures by depressing nerve and muscle activity in the mother’s brain and spinal cord. The Magpie Trial proved its power, cutting the rate of eclampsia by more than half.

• How it’s given: 4 to 6 grams IV loading dose over 15–20 minutes, followed by 1 to 2 grams per hour maintenance.

• How long: Continued for 24 hours after delivery or the last seizure.

2. Fetal Neuroprotection (Not FDA-Approved)
A generation later, magnesium sulfate found a second life—as a protector of the preterm brain. Babies born before 32 weeks’ gestation whose mothers received magnesium were less likely to develop cerebral palsy. The effect is not small. Major studies and meta-analyses show a roughly 30% reduction in severe motor impairment.

• How it’s given: 4 to 6 grams IV loading dose over 20–30 minutes, then 1 gram per hour up to 24 hours or until birth.

• Who receives it: Women expected to deliver before 32 weeks due to labor, ruptured membranes, or maternal complications.

Both indications use nearly the same drug and dosage. The difference is purpose: one treats the mother, the other protects the fetus.

The Safety Problem: A Powerful Drug With a Narrow Margin

Despite its benefits, magnesium sulfate is among the most dangerous medications on the labor and delivery floor. It is consistently listed by the Institute for Safe Medication Practices (ISMP) as a “high-alert medication”, a drug that can cause significant harm or death if used in error. The reason is simple: a small difference between therapeutic and toxic levels can mean respiratory arrest, cardiac collapse, or death.

Typical maternal toxicity warning signs include:

• The mother stops breathing

• Loss of deep tendon reflexes

• Drowsiness or confusion

• Respiratory rate below 12 per minute

• Urine output less than 25–30 mL/hour

• Cardiac arrhythmias or arrest at high serum levels

The antidote, 10 mL of 10% calcium gluconate IV, is lifesaving, but only if available and administered promptly. Many hospitals keep it right at bedside.

A Scenario That Still Happens

A 28-year-old woman with severe preeclampsia is admitted at 34 weeks. Her nurse begins the magnesium sulfate infusion after a 6-gram bolus. The infusion pump is accidentally programmed at 100 mL/hour instead of 10 mL/min. Within minutes, the patient becomes lethargic and stops breathing. Her reflexes are absent. A code is called. Calcium gluconate is not immediately available in the room. The team resuscitates her, but she sustains an anoxic injury. The baby is delivered urgently by cesarean and survives.

This is not a fictional story. Similar cases appear in malpractice records across the country. Most involve pump errors, misprogrammed doses, or failure to monitor reflexes and respirations. Or even using differet solutions of Magnesium sulfate. Magnesium sulfate toxicity can develop silently within minutes, especially if renal function is impaired.

The two main forms are highly concentrated solutions and pre-diluted solutions:

1. Highly Concentrated Solutions

The most common concentrated form is Magnesium Sulfate Injection, USP 50% (500 mg/mL).

• This is a concentrated solution that must be diluted to a concentration of 20% or less before intravenous (IV) infusion to prevent hypermagnesemia and other risks.

• The undiluted 50% solution is sometimes used for deep intramuscular (IM) injection in adults, but dilution is required for IM injection in children.

2. Pre-Diluted Solutions (Ready for IV Use)

Magnesium sulfate is also supplied in lower concentrations, often mixed with an IV solution like 5% Dextrose in Water ($\text{D5W}$) or Water for Injection, and is ready for intravenous infusion. Common pre-diluted concentrations include:

• 4% (40 mg/mL)

• 8% (80 mg/mL)

• 1% (10 mg/mL)

The specific concentration used depends on the medical condition being treated, whether it’s for a loading dose or maintenance infusion, and the route of administration.

Giving It Safely

Safe magnesium administration requires discipline, vigilance, and teamwork. It also requires a very clear policy and labels that are visible on the IV solutions.

Key safety practices include:

• Use premixed solutions only. Never allow staff to mix magnesium sulfate manually. Premixed 40 g/1000 mL bags reduce human error.

• Color code the label. Make sure staff knows the difference.

• Always use a smart infusion pump with an obstetric drug library and dose limits.

• Do regular huddles. This ensures everyone on L&D is aware.

• Never administer without a documented attending order that specifies indication, dose, and monitoring plan.

• Continuous monitoring of respiratory rate, reflexes, and urine output is mandatory.

• Keep calcium gluconate at bedside and ensure all staff know its location and dose.

• Stop the infusion immediately if reflexes disappear or respirations fall below 12.

• Do not run multiple magnesium drips for different indications concurrently. If neuroprotection and preeclampsia overlap, use one protocol and document the indication.

• Educate every nurse and resident at least annually through simulation and competency checks.

The line between therapeutic and toxic levels is thin. The margin for error is thinner still.

The Ethical Dimension

Using magnesium sulfate for neuroprotection remains off-label, despite universal endorsement. Ethically, that fact must be disclosed. Patients have the right to know that while the treatment is standard and evidence-based, it is not FDA-approved for protecting the fetal brain. The American Medical Association and ACOG both require disclosure of off-label use when it is material to informed decision-making. Yet many clinicians skip this detail, assuming it adds unnecessary fear.

But omission is not kindness. It is condescension. Patients can handle complexity if it’s explained simply:

“This medicine is approved to prevent seizures in women with preeclampsia, and we also use it to protect very premature babies’ brains. That second use is not on the drug’s label, but strong research supports it. We’ll monitor you closely because high doses can affect breathing.”

That 20-second explanation turns a paternalistic order into a transparent partnership.

Why the FDA Hasn’t Acted

The FDA never reviewed magnesium sulfate for fetal neuroprotection simply because no one applied. The drug is old, generic, and unprofitable. Conducting the necessary regulatory trials would cost more than any company could recover. It is not a matter of safety or science, but of economics. As with corticosteroids for lung maturity and misoprostol for induction, the system favors profit-driven innovation over public good.

Lessons for Labor and Delivery Units

Every labor unit should treat magnesium sulfate as a critical medication, not a routine one. That means standardized orders, simulation training, and immediate access to antidote kits. Many hospitals now require a second nurse to verify all pump settings before infusion begins, a small step that prevents tragedy.

Clinicians should also document the specific indication each time magnesium sulfate is ordered. “For preeclampsia prophylaxis” and “for fetal neuroprotection” are not interchangeable. Confusion in documentation can lead to miscommunication, overlapping infusions, or errors in duration.

Patients should provide informed consent and be aware of symptoms of intoxication.

The Paradox of Trust

Magnesium sulfate symbolizes both the power and peril of modern obstetrics. It demonstrates how deeply we can save life—and how easily we can lose it through complacency. Its dual purpose forces us to remember that drugs don’t save lives, systems do. When vigilance fades, even good medicine becomes dangerous.

Reflection / Closing

Magnesium sulfate has two stories: one of triumph, one of warning. It protects mothers from seizures and babies from brain injury, yet it can harm both if used carelessly or explained incompletely. The drug’s chemistry is fixed; our responsibility is not. Safety lies in the details, and ethics lies in the truth. Every infusion should carry two commitments: to give carefully and to speak honestly.