magnesium sulfate (Rx)

Brand and Other Names:MgSO4
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Dosing & Uses

AdultPediatric

Dosage Forms & Strengths

injectable solution

  • 40mg/mL
  • 80mg/mL
  • 50%

infusion solution

  • 1g/100mL
  • 2g/100mL

Hypomagnesemia

Mild: 1 g IM q6hr for 4 doses

Severe

  • Asymptomatic: 4-8 g at ≤1 g/hr
  • Symptomatic: 4-8 g at ≤4 g over 4-5 min

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) IV in combination with either (a) up to 10 g (20 mL of undiluted 50% solution) divided and administered IM into each buttock or (b) after initial IV dose, 1-2 g/hr IV; may administer q4hr as necessary

Torsades de Pointes

With pulse (ACLS): 1-2 g slow IV (diluted in 50-100 mL D5W) over 5-60 minutes, then 0.5-1 g/hr 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 tocolytic to stop preterm labor

Loading dose: 4-6 g IV over 20 minutes; maintenance: 2-4 g/hr 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 hypocalcemia in developing fetus resulting in neonates with skeletal abnormalities related to osteopenia

Dosing Modifications

Severe renal impairment: Do not exceed 20 g/48 hr

Dosage Forms & Strengths

injectable solution

  • 40mg/mL
  • 80mg/mL
  • 50%

infusion solution

  • 1g/100mL
  • 2g/100mL

Acute Nephritis

100 mg/kg IM q4-6hr PRN or 20-40 mg/kg IM PRN  

Severe: 100-200 mg/kg IV as 1-3% solution; administer total dose within 1 hr, one-half within first 15-20 minutes

Hypomagnesemia

IV/IM: 25-50 mg/kg q4-6hr for 3-4 doses PRN  

PO: 100-200 mg/kg q6hr

Bronchospasm (Off-label)

25-50 mg/kg IV over 10-20 minutes

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Interactions

Interaction Checker

and magnesium sulfate

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            Adverse Effects

            Frequency Not Defined

            Circulatory collapse

            Respiratory paralysis

            Hypothermia

            Pulmonary edema

            Depressed reflexes

            Hypotension

            Flushing

            Drowsiness

            Depressed cardiac function

            Diaphoresis

            Hypocalcemia

            Hypophosphatemia

            Hyperkalemia

            Visual changes

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            Warnings

            Contraindications

            Hypersensitivity

            Myocardial damage, diabetic coma, heart block

            Hypermagnesemia

            Hypercalcemia

            Administration during 2 hours preceding delivery for mothers with toxemia of pregnancy

            Cautions

            Fetal skeletal demineralization, hypocalcemia, and hypermagnesemia abnormalities reported with continuous long-term use (ie, longer than 5-7 days) for off-label treatment of preterm labor in pregnant women; the effect on the developing fetus may result in neonates with skeletal abnormalities

            In patients with renal impairment, ensure that renal excretory capacity is not exceeded

            Use with caution in digitalized patients

            Use with extreme caution in patients with myasthenia gravis or other neuromuscular disease

            Hypomagnesemia is usually associated with hypokalemia (potassium levels must be normalized)

            Monitor renal function, blood pressure, respiratory rate, and deep tendon reflex when magnesium sulfate is administered parenterally

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            Pregnancy & Lactation

            Pregnancy category: D

            Fetal skeletal demineralization, hypocalcemia, and hypermagnesemia reported with continuous long-term use (ie, longer than 5-7 days) for off-label treatment of preterm labor in pregnant women; the effect on the developing fetus may result in neonates with skeletal abnormalities

            Continuous administration of magnesium sulfate injection to treat preterm labor is not approved and that the safety and efficacy of use for this indication are not established

            Lactation: Safe

            Pregnancy Categories

            A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.

            B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.

            C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.

            D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.

            X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.

            NA: Information not available.

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            Pharmacology

            Mechanism of Action

            Depresses CNS, blocks peripheral neuromuscular transmission, produces anticonvulsant effects; decreases amount of acetylcholine released at end-plate by motor nerve impulse

            Slows rate of SA node impulse formation in myocardium and prolongs conduction time

            Promotes movement of calcium, potassium, and sodium in and out of cells and stabilizes excitable membranes

            Promotes osmotic retention of fluid in colon, causing distention and increased peristaltic activity, which subsequently results in bowel evacuation

            Absorption

            Onset (anticonvulsant): IV, immediate; IM, 1 hr

            Duration (anticonvulsant): IV, 30 min; IM, 3-4 hr

            Distribution

            Protein bound: 30%

            Extracellular distribution: 1-2%

            Elimination

            Excretion: Urine

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            Administration

            IV Incompatibilities

            Solution: IV fat emulsion 10%

            Additive: Amphotericin B, cyclosporine, dobutamine, polymyxin B sulfate, procaine, sodium bicarbonate

            Y-site: Alatrofloxacin, amiodarone (at 500 mg/mL MgSO4; may be compatible at 20 mg/mL), amphotericin B cholesteryl sulfate, cefepime, ciprofloxacin (?)

            IV Preparation

            Intermittent infusion: Dilute to 60 mg/mL

            IV Administration

            Infuse over 2-4 hr (hypomagnesemia) or as otherwise specified; rate not to exceed 125 mg/kg/hr

            In severe cases, half of the dose may be infused over first 15-20 minutes

            Rapid infusions (over 10-20 minutes) may be used for treatment of severe asthma or torsades de pointes ventricular tachycardia

            Cautiously infuse diluted solution through patent IV line

            IM Administration

            Dilute to maximum concentration of 200 mg/mL before injection

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            Formulary

            FormularyPatient Discounts

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            Tier Description
            1 This drug is available at the lowest co-pay. Most commonly, these are generic drugs.
            2 This drug is available at a middle level co-pay. Most commonly, these are "preferred" (on formulary) brand drugs.
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            NC NOT COVERED – Drugs that are not covered by the plan.
            Code Definition
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            Medscape prescription drug monographs are based on FDA-approved labeling information, unless otherwise noted, combined with additional data derived from primary medical literature.