Magnesium Sulfate Dosage

Medically reviewed by Drugs.com. Last updated on Jun 12, 2024.

Usual Adult Dose for Hypomagnesemia

1 gram IM every 6 hours for 4 doses (mild hypomagnesemia) or as much as 250 mg/kg IM within a 4-hour period (severe hypomagnesemia)
OR
5 grams in 1 liter of appropriate diluent IV over 3 hours

• Do not exceed IV infusion rate of 150 mg/minute

Comments:

• Appropriate diluents include 5% dextrose or 0.9% sodium chloride.
• Use caution to prevent exceeding renal excretory capacity.
• May be given undiluted intramuscularly.
• Carefully adjust dosage to individual requirements and response.
• Discontinue as soon as the desired effect is obtained.

Usual Adult Dose for Atrial Tachycardia

3 to 4 grams (30 to 40 mL of a 10% solution) IV over 30 seconds

Comments:

• Use with EXTREME CAUTION.
• Use only if simpler methods have failed and there is no evidence of myocardial damage.

Use: Paroxysmal atrial tachycardia

Usual Adult Dose for Pre-eclampsia/Eclampsia

Severe pre-eclampsia or eclampsia:
Initial dose: 4 to 5 grams IV in 250 mL of appropriate diluent, with simultaneous IM administration of up to 5 grams (10 mL undiluted solution) in EACH buttock; total dose: 10 to 14 grams

• Initial IV dose of 4 grams may also be diluted to a 10% or 20% solution and injected IV over 3 to 4 minutes

Maintenance dose: 4 to 5 grams IM into alternate buttocks every 4 hours as needed
OR
Maintenance dose: 1 to 2 grams/hour IV by constant infusion

• Continue therapy until paroxysms cease

Maximum dose: 30 to 40 grams/day

Comments:

• Appropriate diluents include 5% dextrose or 0.9% sodium chloride.
• A serum magnesium level of 6 mg/100 mL is considered optimal for seizure control.
• The need to continue therapy is based on the continuing presence of patellar reflex and adequate respiratory function.
• Continuous maternal administration beyond 5 to 7 days can cause fetal abnormalities.
• Monitor serum magnesium and patient clinical status to avoid overdosage.
• Clinical indications of a safe dose include presence of patellar reflex (knee jerk) and absence of respiratory depression (about 16 breaths/minute or more).
• Test patellar reflex before repeat doses and do not administer magnesium if absent.
• Deep tendon reflexes begin to diminish at magnesium levels above 4 mEq/L.
• Reflexes may be absent at 10 mEq/L, where there is potential for respiratory paralysis.
• An injectable calcium salt should be immediately available to counteract magnesium intoxication.

Uses: Prevention and control of seizures in pre-eclampsia and eclampsia

Usual Adult Dose for Constipation

2 to 4 level teaspoons dissolved in 8 ounces water orally

• Repeat dose in 4 hours if needed.

Maximum dose: 2 doses per day

Uses: Cathartic or laxative

Usual Adult Dose for Barium Poisoning

1 to 2 grams IV

• Do not exceed IV infusion rate of 150 mg/minute

Use: To counteract the muscle-stimulating effects of barium poisoning

Usual Adult Dose for Seizures

1 gram intramuscularly or IV

• Do not exceed IV infusion rate of 150 mg/minute

Use: Seizures associated with epilepsy, glomerulonephritis, or hypothyroidism

Usual Adult Dose for Cerebral Edema

2.5 grams (25 mL of a 10% solution) IV

• Do not exceed IV infusion rate of 150 mg/minute

Use: Reduction of cerebral edema

Usual Pediatric Dose for Constipation

Epsom Salt:

12 years and older: 2 to 4 level teaspoons dissolved in 8 ounces water orally
6 to 11 years: 1 to 2 level teaspoons dissolved in 8 ounces of water orally
Under 6 years: Not recommended
Maximum dose: 2 doses per day

Comments:

• Repeat dose in 4 hours if needed.
• Generally produces a bowel movement in 30 minutes to 6 hours.

Uses: Cathartic or laxative

Renal Dose Adjustments

Use with caution.

• Magnesium is removed from the body solely by the kidneys.
• Parenteral use in renal insufficiency may lead to magnesium intoxication.
• Urine output should be maintained at 100 mL or more during the 4 hours preceding each dose.
• Monitoring serum magnesium and patient clinical status is essential to avoid overdose in toxemia of pregnancy.
• Reserve IV use for immediate control of life-threatening convulsions.

Prevention/Control of pre-eclamptic and eclamptic seizures:

• Maximum dosage is 20 grams/48 hours for severe renal insufficiency.
• Obtain serum magnesium concentrations frequently.
• Continuous maternal administration beyond 5 to 7 days can cause fetal abnormalities.

Liver Dose Adjustments

No adjustment recommended.

Dialysis

Data not available

Other Comments

Administration advice:

• Solutions for IV administration must be diluted to a concentration of 20% or less.
• Deep intramuscular administration of the undiluted parenteral solution is appropriate for adults.
• Dilute the parenteral solution to a concentration of 20% or less for IM administration to children.

IV compatibility:

• Compatible with 5% dextrose and 0.9% sodium chloride solutions
• The manufacturer product information should be consulted for a list of incompatible substances.

Monitoring:

• Monitor serum magnesium and patient clinical status to avoid overdosage in toxemia of pregnancy.
• Clinical indications of a safe dose include presence of patellar reflex (knee jerk) and absence of respiratory depression (about 16 breaths/minute or more).
• Test patellar reflex before repeat doses and do not administer magnesium if absent.
• Deep tendon reflexes begin to diminish at magnesium levels above 4 mEq/L.
• Reflexes may be absent at 10 mEq/L, where there is potential for respiratory paralysis.
• Serum magnesium levels of 3 to 6 mg/100 mL (2.5 to 5 mEq/L) are usually sufficient to control convulsions.
• An injectable calcium salt should be immediately available to counteract magnesium intoxication in toxemia of pregnancy.

Frequently asked questions

• When is the best time to take magnesium, morning or night?
• Should I take magnesium with or without food?
• Does magnesium help with restless leg syndrome (RLS)?
• Does magnesium help with headaches and migraines?
• Does magnesium help with weight loss?

See also:

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Medical Disclaimer