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Magnesium Sulfate

Pronunciation

Pronunciation

(mag NEE zhum SUL fate)

Index Terms

  • Epsom Salts
  • MgSO4 (error-prone abbreviation)

Dosage Forms

Excipient information presented when available (limited, particularly for generics); consult specific product labeling. [DSC] = Discontinued product

Capsule, Oral:

Generic: 70 mg

Granules, Oral:

Epsom Salt: (454 g, 1810 g, 1816 g)

GoodSense Epsom Salt: (1810 g)

Solution, Injection:

Generic: 50% (2 mL, 10 mL, 20 mL, 50 mL [DSC])

Solution, Injection [preservative free]:

Generic: 50% (20 mL, 50 mL)

Solution, Intravenous:

Generic: 10 mg/mL (100 mL); 20 mg/mL (500 mL); 2 g/50 mL (50 mL); 4 g/50 mL (50 mL); 4 g/100 mL (100 mL); 20 g/500 mL (500 mL); 40 g/1000 mL (1000 mL); 40 mg/mL (50 mL, 100 mL, 500 mL, 1000 mL); 80 mg/mL (50 mL)

Brand Names: U.S.

  • Epsom Salt [OTC]
  • GoodSense Epsom Salt [OTC]

Pharmacologic Category

  • Anticonvulsant, Miscellaneous
  • Electrolyte Supplement, Parenteral
  • Magnesium Salt

Pharmacology

When taken orally, magnesium promotes bowel evacuation by causing osmotic retention of fluid which distends the colon with increased peristaltic activity; parenterally, magnesium decreases acetylcholine in motor nerve terminals and acts on myocardium by slowing rate of S-A node impulse formation and prolonging conduction time. Magnesium is necessary for the movement of calcium, sodium, and potassium in and out of cells, as well as stabilizing excitable membranes.

Intravenous magnesium may improve pulmonary function in patients with asthma; causes relaxation of bronchial smooth muscle independent of serum magnesium concentration.

Absorption

Oral: Slow and poor (approximately one-third absorbed)

Distribution

Bone (50% to 60%); extracellular fluid (1% to 2%) (IOM, 1997)

Excretion

Urine (as magnesium); feces (as unabsorbed drug)

Onset of Action

Anticonvulsant: IM: 1 hour; Anticonvulsant: IV: Immediate; Laxative: Oral: 0.5 to 6 hours

Duration of Action

Anticonvulsant activity: IM: 3-4 hours; IV: 30 minutes

Protein Binding

30%, to albumin

Use: Labeled Indications

Oral: Laxative for the relief of occasional constipation (OTC labeling)

Parenteral: Treatment and prevention of hypomagnesemia; prevention and treatment of seizures in severe pre-eclampsia or eclampsia, pediatric acute nephritis; treatment of cardiac arrhythmias (VT/VF) caused by hypomagnesemia

Topical: Soaking aid for minor cuts and bruises (OTC labeling)

Use: Unlabeled

Asthma exacerbation (life-threatening) unresponsive to 1 hour intensive conventional treatment; torsade de pointes or VF/pulseless VT associated with torsade de pointes

Contraindications

Hypersensitivity to any component of the formulation; heart block; myocardial damage; IV use for pre-eclampsia/eclampsia during the 2 hours prior to delivery

Dosing: Adult

Dose represented as magnesium sulfate unless stated otherwise. Note: Serum magnesium is poor reflection of repletional status as the majority of magnesium is intracellular; serum concentrations may be transiently normal for a few hours after a dose is given, therefore, aim for consistently high normal serum concentrations in patients with normal renal function for most efficient repletion.

Note: 1 g of magnesium sulfate = 98.6 mg elemental magnesium = 8.12 mEq elemental magnesium = magnesium 4.06 mmol

Constipation (occasional): Oral: 2 to 4 level teaspoons of granules dissolved in 8 ounces of water; may repeat in 6 hours. Do not exceed 2 doses per day.

Eclampsia/pre-eclampsia (severe):

Manufacturer's labeling: IV: An initial total dose of 10 to 14 g administered as follows: 4 g infusion with simultaneous IM injections of 4 to 5 g in each buttock. After the initial IV/IM doses, may administer a 1 to 2 g/hour continuous infusion or may follow with IM doses of 4 to 5 g into alternate buttocks every 4 hours as necessary. Maximum: 40 g/24 hours. IV use for pre-eclampsia/eclampsia is contraindicated during the 2 hours prior to delivery.

Alternate dosing (off-label): IV: 4 to 6 g loading dose followed by 1 to 2 g/hour continuous infusion for at least 24 hours (ACOG, 2013)

Hypomagnesemia, treatment: Note: Treatment depends on severity and clinical status. In asymptomatic patients (when oral route is available), oral replacement therapy is a better replacement method than IV administration.

Mild deficiency: IM: Manufacturer's labeling: 1 g every 6 hours for 4 doses, or as indicated by serum magnesium concentrations

Mild-to-moderate (serum concentration 1 to 1.5 mg/dL): IV: 1 to 4 g (up to 0.125 g/kg), administer at ≤1 g/hour if asymptomatic; do not exceed 12 g over 12 hours (Kraft, 2005). Note: Additional supplementation may be required after the initial dose with replenishment occurring over several days.

Severe deficiency:

IM: Manufacturer’s labeling: Up to 250 mg/kg within a 4-hour period

IV:

Severe (<1 mg/dL): 4 to 8 g (up to 0.1875 g/kg), administer at ≤1 g/hour if asymptomatic; in symptomatic patients, may administer ≤4 g over 4-5 minutes (Kraft, 2005)

With polymorphic VT (including torsade de pointes): IV push: 1 to 2 g (ACLS, 2010)

Obesity: Weight >130% of ideal body weight (IBW) or body mass index (BMI) ≥30 kg/m2: When determining maximum per kg dose for replacement, some clinicians suggest using adjusted body weight (AdjBW) (Kraft, 2005).

AdjBW (men) = ([wt (kg) -IBW (kg)] x 0.3) + IBW

AdjBW (women) = ([wt (kg) -IBW (kg)] x 0.25) + IBW

Hypomagnesemia, prevention (parenteral nutrition supplementation): IV: 8 to 20 mEq elemental magnesium daily (ASPEN [Mirtallo, 2004])

Soaking aid: Topical: Dissolve 2 cupfuls of granules per gallon of warm water; may also soak a towel with the solution to apply as a wet dressing.

Asthma (acute severe exacerbations) (off-label use): IV: 2 g as a single dose over 20 minutes (NAEPP, 2007; GINA, 2015); recommended as adjunctive therapy for severe life-threatening exacerbations and for exacerbations that remain severe after 1 hour of intensive conventional therapy (NAEPP, 2007)

Torsade de pointes or VF/pulseless VT associated with torsade de pointes (off-label use): IV, I.O.: 1 to 2 g over 15 minutes (ACLS, 2010)

RDA (IOM, 1997):

Adults 19 to 30 years:

Females: 310 mg elemental magnesium daily

Pregnant females: 350 mg elemental magnesium daily

Breast-feeding females: 310 mg elemental magnesium daily

Males: 400 mg elemental magnesium daily

Adults ≥31 years:

Females: 320 mg elemental magnesium daily

Pregnant females: 360 mg elemental magnesium daily

Breast-feeding females: 320 mg elemental magnesium daily

Males: 420 mg elemental magnesium daily

Dosing: Geriatric

Refer to adult dosing.

Dosing: Pediatric

Dose represented as magnesium sulfate unless stated otherwise. Note: Serum magnesium is poor reflection of repletional status as the majority of magnesium is intracellular; serum concentrations may be transiently normal for a few hours after a dose is given, therefore, aim for consistently high normal serum concentrations in patients with normal renal function for most efficient repletion.

Note: 1 g of magnesium sulfate = 98.6 mg elemental magnesium = 8.12 mEq elemental magnesium = magnesium 4.06 mmol

Constipation (occasional): Oral:

Children 6 to <12 years: 1 to 2 level teaspoons of granules dissolved in water; may repeat in 4 to 6 hours (maximum: 2 doses/24 hours)

Children ≥12 years and Adolescents: Refer to adult dosing.

Hypomagnesemia, treatment: Note: Treatment depends on severity and clinical status: IV, I.O.: 25 to 50 mg/kg/dose over 10 to 20 minutes (over several minutes for torsade de pointes); maximum single dose: 2000 mg (PALS, 2010)

Hypomagnesemia, prevention (parenteral nutrition supplementation) (ASPEN [Mirtallo, 2004]): IV:

≤50 kg: 0.3 to 0.5 mEq elemental magnesium/kg/day

>50 kg: 10 to 30 mEq elemental magnesium daily

Asthma (acute severe exacerbations) (off-label use): IV: Children and Adolescents: 25 to 75 mg/kg (maximum: 2000 mg) as a single dose over 20 to 60 minutes (GINA 2015; NAEPP, 2007); recommended as adjunctive therapy for severe life-threatening exacerbations and for exacerbations that remain severe after 1 hour of intensive conventional therapy (NAEPP, 2007)

RDA (IOM, 1997): Children

1 to 3 years: 80 mg elemental magnesium daily

4 to 8 years: 130 mg elemental magnesium daily

9 to 13 years: 240 mg elemental magnesium daily

14 to 18 years:

Females: 360 mg elemental magnesium daily

Pregnant females: 400 mg elemental magnesium daily

Breast-feeding females: 360 mg elemental magnesium daily

Males: 410 mg elemental magnesium daily

Dosing: Renal Impairment

Hypomagnesemia: Renal dysfunction: Reduce dose by 50% (Kraft, 2005). Use with caution; monitor for hypermagnesemia; Close monitoring is required.

Pre-eclampsia/eclampsia: Severe renal impairment: Per the manufacturer, do not exceed 20 grams during a 48 hour period.

Dosing: Hepatic Impairment

No dosage adjustment necessary.

Dosing: Obesity

Refer to indication-specific dosing for obesity-related information (may not be available for all indications).

Reconstitution

IV: Dilute to a ≤20% solution for IV infusion.

IM: A 25% or 50% concentration may be used for adults and dilution to a ≤20% solution is recommended for children.

Oral: Dissolve granules in 8 ounces of water prior to administration. May add lemon juice to improve taste.

Topical: Dissolve 2 cups of granules per gallon of warm water to use as a soaking aid.

Administration

Injection: May be administered IM or IV

IM: Must be diluted prior to administration for children (Adults: 25% or 50% concentration; Children: ≤20% diluted solution)

IV: Must be diluted to a ≤20% solution for IV infusion and may be administered IV push, IVPB, or continuous IV infusion. When giving IV push, must dilute first and should generally not be given any faster than 150 mg/minute; may administer over 1 to 2 minutes in patients with persistent pulseless VT or VF with known hypomagnesemia (Dager, 2006). ACLS guidelines recommend administration over 15 minutes in patients with torsade de pointes (ACLS, 2010). In patients not in cardiac arrest, hypotension and asystole may occur with rapid administration. In patients with asthma (acute severe exacerbation) (off-label use), may administer single dose over 20 minutes to 60 minutes (GINA 2015; NAEPP 2007).

Maximal rate of infusion: Up to 50% of an IV dose may be eliminated in the urine, therefore, slower administration may improve retention (maximum rate: 1 g/hour in asymptomatic patients). For doses <6 g, infuse over 8 to 12 hours and for larger doses infuse over 24 hours if patient is asymptomatic. If patient is severely symptomatic (or has conditions such as preeclampsia or eclampsia) more aggressive therapy (≤4 g over 4 to 5 minutes) may be required; patients should be closely monitored (Kraft, 2005).

Oral: When used as a laxative, dissolve dose in 8 ounces of water prior to ingesting. Lemon juice may be added to the solution to improve the taste.

Topical: May dissolve granules to prepare a solution for use as a soaking aid or as a compress. To make a compress, use a towel to apply as a wet dressing.

Dietary Considerations

Whole grains, legumes and dark-green leafy vegetables are dietary sources of magnesium (IOM, 1997).

Compatibility

Stable in D5W, D10W, D51/4NS, D5NS, LR, NS, R; incompatible with fat emulsion 10%.

Y-site administration: Incompatible with amphotericin B cholesteryl sulfate complex, cefepime, drotrecogin alfa.

Compatibility in syringe: Incompatible with calcium chloride, pantoprazole, phytonadione.

Storage

Prior to use, store at room temperature of 20°C to 25°C (68°F to 77°F). Do not freeze. Refrigeration of solution may result in precipitation or crystallization.

Drug Interactions

Alfacalcidol: May increase the serum concentration of Magnesium Salts. Consider therapy modification

Alpha-Lipoic Acid: Magnesium Salts may decrease the absorption of Alpha-Lipoic Acid. Alpha-Lipoic Acid may decrease the absorption of Magnesium Salts. Consider therapy modification

Bisphosphonate Derivatives: Magnesium Salts may decrease the serum concentration of Bisphosphonate Derivatives. Management: Avoid administration of oral magnesium salts within: 2 hours before or after tiludronate/clodronate/etidronate; 60 minutes after oral ibandronate; or 30 minutes after alendronate/risedronate. Exceptions: Pamidronate; Zoledronic Acid. Consider therapy modification

Calcitriol (Systemic): May increase the serum concentration of Magnesium Salts. Consider therapy modification

Calcium Channel Blockers: May enhance the adverse/toxic effect of Magnesium Salts. Magnesium Salts may enhance the hypotensive effect of Calcium Channel Blockers. Monitor therapy

Calcium Polystyrene Sulfonate: Laxatives (Magnesium Containing) may enhance the adverse/toxic effect of Calcium Polystyrene Sulfonate. More specifically, concomitant use of calcium polystyrene sulfonate with magnesium-containing laxatives may result in metabolic alkalosis or with sorbitol may result in intestinal necrosis. Management: Avoid concomitant use of calcium polystyrene sulfonate (rectal or oral) and magnesium-containing laxatives. Avoid combination

CNS Depressants: Magnesium Sulfate may enhance the CNS depressant effect of CNS Depressants. Monitor therapy

Deferiprone: Magnesium Salts may decrease the serum concentration of Deferiprone. Management: Separate administration of deferiprone and oral medications or supplements that contain polyvalent cations by at least 4 hours. Consider therapy modification

Dolutegravir: Magnesium Salts may decrease the serum concentration of Dolutegravir. Management: Administer dolutegravir at least 2 hours before or 6 hours after oral magnesium salts. Consider therapy modification

Eltrombopag: Magnesium Salts may decrease the serum concentration of Eltrombopag. Management: Administer eltrombopag at least 2 hours before or 4 hours after oral administration of any magnesium-containing product. Consider therapy modification

Gabapentin: Magnesium Salts may enhance the CNS depressant effect of Gabapentin. Specifically, high dose intravenous/epidural magnesium sulfate may enhance the CNS depressant effects of gabapentin. Magnesium Salts may decrease the serum concentration of Gabapentin. Management: Administer gabapentin at least 2 hours after oral magnesium salts administration. Monitor patients closely for evidence of reduced response to gabapentin therapy. Monitor for CNS depression if high dose IV/epidural magnesium sulfate is used. Consider therapy modification

Levothyroxine: Magnesium Salts may decrease the serum concentration of Levothyroxine. Management: Separate administration of oral levothyroxine and oral magnesium salts by at least 4 hours. Consider therapy modification

Multivitamins/Fluoride (with ADE): Magnesium Salts may decrease the serum concentration of Multivitamins/Fluoride (with ADE). Specifically, magnesium salts may decrease fluoride absorption. Management: To avoid this potential interaction separate the administration of magnesium salts from administration of a fluoride-containing product by at least 1 hour. Consider therapy modification

Mycophenolate: Magnesium Salts may decrease the serum concentration of Mycophenolate. Management: Separate doses of mycophenolate and oral magnesium salts. Monitor for reduced effects of mycophenolate if taken concomitant with oral magnesium salts. Consider therapy modification

Neuromuscular-Blocking Agents: Magnesium Salts may enhance the neuromuscular-blocking effect of Neuromuscular-Blocking Agents. Monitor therapy

Phosphate Supplements: Magnesium Salts may decrease the serum concentration of Phosphate Supplements. Management: This applies only to oral phosphate and magnesium administration. Administer oral phosphate supplements at least 1 hour before, or 2 hours after, oral magnesium salt administration. Exceptions: Sodium Glycerophosphate Pentahydrate. Consider therapy modification

Quinolone Antibiotics: Magnesium Salts may decrease the serum concentration of Quinolone Antibiotics. Management: Administer oral quinolones at least several hours before (4 h for moxi- and sparfloxacin, 2 h for others) or after (8 h for moxi-, 6 h for cipro-, 4 h for lome-, 3 h for gemi-, and 2 h for levo-, nor-, or ofloxacin or nalidixic acid) oral magnesium salts. Exceptions: LevoFLOXacin (Oral Inhalation). Consider therapy modification

Raltegravir: Magnesium Salts may decrease the serum concentration of Raltegravir. Management: Avoid the use of oral / enteral magnesium salts with raltegravir. No dose separation schedule has been established that adequately reduces the magnitude of interaction. Avoid combination

Sodium Polystyrene Sulfonate: Laxatives (Magnesium Containing) may enhance the adverse/toxic effect of Sodium Polystyrene Sulfonate. More specifically, concomitant use of sodium polystyrene sulfonate with magnesium-containing laxatives may result in metabolic alkalosis or with sorbitol may result in intestinal necrosis. Management: Avoid concomitant use of sodium polystyrene sulfonate (rectal or oral) and magnesium-containing laxatives. Avoid combination

Tetracycline Derivatives: Magnesium Salts may decrease the absorption of Tetracycline Derivatives. Only applicable to oral preparations of each agent. Consider therapy modification

Trientine: May decrease the serum concentration of Magnesium Salts. Magnesium Salts may decrease the serum concentration of Trientine. Consider therapy modification

Adverse Reactions

Adverse effects on neuromuscular function may occur at lower concentrations in patients with neuromuscular disease (eg, myasthenia gravis).

Frequency not defined:

Cardiovascular: Flushing (IV; dose related), hypotension (IV; rate related), vasodilation (IV; rate related)

Endocrine & metabolic: Hypermagnesemia

Warnings/Precautions

Disease-related concerns:

• Neuromuscular disease: Use with extreme caution in patients with myasthenia gravis or other neuromuscular disease.

• Renal impairment: Use with caution in patients with renal impairment; accumulation of magnesium may lead to magnesium intoxication.

Special populations:

• Obstetrics: Vigilant monitoring and safe administration techniques (ISMP, 2005) recommended to avoid potential for errors resulting in toxicity. Monitor mother and fetus closely. Use longer than 5 to 7 days may cause adverse fetal events.

Dosage form specific issues:

• Aluminum: The parenteral product may contain aluminum; toxic aluminum concentrations may be seen with high doses, prolonged use, or renal dysfunction. Premature neonates are at higher risk due to immature renal function and aluminum intake from other parenteral sources. Parenteral aluminum exposure of >4 to 5 mcg/kg/day is associated with CNS and bone toxicity; tissue loading may occur at lower doses (Federal Register, 2002). See manufacturer’s labeling.

Other warnings/precautions:

• Appropriate use: Unlikely to effectively terminate irregular/polymorphic VT (with normal baseline QT interval) (AHA [Neumar 2010]).

• Electrolyte abnormalities: Concurrent hypokalemia or hypocalcemia can accompany a magnesium deficit. Hypomagnesemia is frequently associated with hypokalemia and requires correction in order to normalize potassium.

• Parenteral administration: Magnesium toxicity can lead to fatal cardiovascular arrest and/or respiratory paralysis.

• Self-medication (OTC Use): When used as a soaking aid, patients should not use if there is evidence of infection or prompt relief is not obtained. When used as a laxative, patients should consult a healthcare provider prior to use if they have: kidney disease; are on a magnesium-restricted diet; have abdominal pain, nausea, or vomiting; change in bowel habits lasting >2 weeks; have already used a laxative for >1 week.

Monitoring Parameters

IV: Rapid administration: ECG monitoring, vital signs, deep tendon reflexes; magnesium concentrations if frequent or prolonged dosing required particularly in patients with renal dysfunction, calcium, and potassium concentrations; renal function

Obstetrics: Patient status including vital signs, oxygen saturation, deep tendon reflexes, level of consciousness, fetal heart rate, maternal uterine activity.

Pregnancy Risk Factor

D

Pregnancy Considerations

Magnesium crosses the placenta; serum concentrations in the fetus are similar to those in the mother (Idama, 1998; Osada, 2002). Continuous maternal use for >5-7 days (in doses such as those used for preterm labor, an off-label use) may cause fetal hypocalcemia and bone abnormalities, as well as fractures in the neonate. Magnesium sulfate injection is used for the prevention and treatment of seizures in pregnant or postpartum women with severe pre-eclampsia or eclampsia (ACOG, 2013). Magnesium sulfate may also be used prior to early preterm delivery to reduce the risk of cerebral palsy (ACOG, 2010; Reeves, 2011). Tocolytics may be used for the short-term (48 hour) prolongation of pregnancy to allow for the administration of antenatal steroids and should not be used prior to fetal viability or when the risks of use to the fetus or mother are greater than the risk of preterm birth; maintenance therapy with tocolytics is ineffective and not recommended. Magnesium sulfate injection may be used in conjunction with tocolytics for neuroprotection (it is not preferred for use as a tocolytic); however, an increased risk of maternal complications may be observed when used in combination with some tocolytic agents (ACOG, 2012).

Patient Education

• Discuss specific use of drug and side effects with patient as it relates to treatment. (HCAHPS: During this hospital stay, were you given any medicine that you had not taken before? Before giving you any new medicine, how often did hospital staff tell you what the medicine was for? How often did hospital staff describe possible side effects in a way you could understand?)

• Patient may experience injection site irritation. Have patient report immediately to prescriber arrhythmia, severe dizziness; passing out; severe loss of strength and energy; sweating a lot; vision changes; confusion; severe flushing; severe edema; muscle weakness; difficulty moving; seizures; severe diarrhea; severe nausea; severe vomiting; black, tarry, or bloody stools; or cramps (HCAHPS).

• Educate patient about signs of a significant reaction (eg, wheezing; chest tightness; fever; itching; bad cough; blue skin color; seizures; or swelling of face, lips, tongue, or throat). Note: This is not a comprehensive list of all side effects. Patient should consult prescriber for additional questions.

Intended Use and Disclaimer: Should not be printed and given to patients. This information is intended to serve as a concise initial reference for healthcare professionals to use when discussing medications with a patient. You must ultimately rely on your own discretion, experience and judgment in diagnosing, treating and advising patients.

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