Magnesium Sulfate and Labetalol: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Labetalol
Magnesium Sulfate
No brand names on record
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Bradycardia and decreased cardiac output (shortness of breath, lightheadedness, or fainting spells)
Interaction Deep Dive
A significant bradycardic event occurred in a pre-eclamptic patient who received magnesium sulfate and labetalol. The patient was treated with labetalol for hypertension and immediately following this infusion received a bolus of magnesium sulfate. The patient became bradycardic and began to lose consciousness. Her symptoms resolved when the magnesium sulfate was temporarily discontinued. Magnesium sulfate was reinstated and no further episodes of bradycardia were experienced1.
Why it happens (mechanism)
Decrease in sinus node rate caused by magnesium
Literature reports
1 report — tap to read
a) A case report involving an 18-year-old female undergoing treatment for preeclampsia demonstrates an interaction with concomitant labetalol and magnesium sulfate leading to bradycardia. The patient was treated in the delivery room at 36 weeks gestation with hydralazine (10 mg intravenous) for hypertension. Her pulse rate subsequently increased from 100 to 150-160 beats per minute. Sinus tachycardia was evident on the electrocardiograph. The patient was subsequently treated with labetalol intravenously. Cardiovascular parameters improved and no further antihypertensive agents were administered. A magnesium sulfate bolus was infused for pre-eclampsia. The patient felt faint and started to lose consciousness approximately 20 minutes after initiation of the infusion. An electrocardiogram revealed that her heart rate had plummeted from 110 to less than 40 beats per minute. At this point, labetalol had been discontinued for at least 30 minutes. The magnesium sulfate infusion was subsequently discontinued and the patient was treated with atropine and oxygen. Her heart rate increased to 70 beats per minute shortly thereafter. Magnesium sulfate was restarted ten minutes after the bradycardic episode and no further episodes of bradycardia were experienced 1.
Common questions
Can I take Magnesium Sulfate and Labetalol together?
Bradycardia and decreased cardiac output (shortness of breath, lightheadedness, or fainting spells) Always confirm with your pharmacist or prescriber before making any change.
How serious is the Magnesium Sulfate and Labetalol interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
How quickly could this interaction happen?
The documented onset is "rapid". Effects can appear quickly, often within about 24 hours of combining the drugs.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Magnesium Sulfate or Labetalol need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there anything you'd monitor while I'm on both?
References (1)
- Pittman J: Magnesium sulphate for pre-eclampsia and a sudden bradycardia. Br J Anaesth 2000; 85:327-328.
Keep reading about Labetalol
Keep reading about Magnesium Sulfate
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