Not e: Dosing units: All doses in this monograph are expressed as magnesium sulfate salt unless stated otherwise. One g of magnesium sulfate salt = 98.6 mg of elemental magnesium = 8.12 mEq of elemental magnesium = 4.06 mmol of elemental magnesium. Serum concentrations: Serum magnesium levels do not correlate well with total body stores as the majority of magnesium is intracellular; serum concentrations may be transiently elevated for a few hours after administration of an IV dose (Kraft 2005).
Asthma (severe exacerbations) (adjunct) (off-label use):
Note: For severe or life-threatening exacerbations in addition to or if nonresponsive to initial therapy (GINA 2020; NAEPP 2007).
IV: 2 g as a single dose over 20 minutes (GINA 2020).
Constipation (alternative agent):
Note: For occasional use only. Use in some patients (eg, in those with cardiac dysfunction, kidney disease) may result in electrolyte disturbances and volume overload (Lembo 2003).
OTC labeling (patient-guided therapy): Oral: 2 to 4 level teaspoons (~10 to 20 g) of granules dissolved in 8 ounces (240 mL) of water; may repeat in 4 hours. Do not exceed 2 doses per day (Guerrera 2009).
Eclampsia/preeclampsia, seizure prophylaxis and treatment:
Note: An optimal regimen has not been identified. Close monitoring (including kidney function [eg, urine output], respiration, and patellar reflexes) is required; monitoring of magnesium levels is recommended for patients with kidney impairment and in patients with signs of toxicity or seizure(s). Adjust dose to avoid maternal toxicity. Calcium gluconate should be available for treating severe magnesium toxicity (ACOG 2020; De Silva 2015; Duley 2010; Long 2017; Pratt 2016).
IV: Initial: 4 to 6 g loading dose over 15 to 30 minutes at onset of labor or induction/cesarean delivery, followed by 1 to 2 g/hour continuous infusion for at least 24 hours after delivery; maximum infusion rate: 3 g/hour. If seizure occurs while receiving magnesium, an additional bolus of 2 to 4 g may be administered over ≥5 minutes with frequent monitoring for toxicity (ACOG 2020; Eclampsia Trial Collaborative Group 1995; Kraft 2005; Norwitz 2022). Product labeling recommends a maximum dose of 40 g per 24 hours; however, this varies among regimens and institutional protocols.
IM (50% concentration): Initial: 10 g loading dose administered as 5 g in each buttock at onset of labor or induction/cesarean delivery, followed by 5 g every 4 hours for at least 24 hours after delivery. Note: Use IM route when unable to establish venous access (ACOG 2020; Altman 2002; Norwitz 2022).
Fetal neuroprotection for imminent preterm birth (maternal administration) (off-label use):
Note: An optimal regimen has not been identified. Close monitoring (including kidney function [eg, urine output], respiration, and patellar reflexes) is required (Simhan 2020). Generally used for pregnancies <32 weeks' gestation with expected delivery within 24 hours (ACOG 2016; Crowther 2003). Regimens vary; consult institutional protocols. An example regimen is listed below:
IV: Initial: 4 g loading dose over 20 to 30 minutes (Crowther 2003; Marret 2007); may follow with a 1 g/hour continuous infusion for a maximum of 24 hours or until delivery, whichever comes first (Crowther 2003).
Hypomagnesemia, treatment:
Note: Recommended dosing and infusion rates may vary among institutional protocols according to severity, clinical status (eg, if postoperative), and type of IV access (Siparsky 2022).
Asymptomatic patients: Note: Oral replacement using a different salt (eg, magnesium chloride) is generally preferred if tolerated (Yu 2021). Slow IV administration (≤1 g/hour) may provide more efficient repletion due to potential for rapid urinary elimination (Kraft 2005). Use IM only if IV access is unavailable (Ayuk 2014). Subsequent dosing may be based on daily serum magnesium concentrations; repletion may take several days (Kraft 2005).
Initial:
Mild deficiency (eg, serum magnesium >1.5 to 1.9 mg/dL):
IV: 1 to 2 g over 1 to 2 hours (Yu 2021).
IM (50% concentration): 1 g every 6 hours for 4 doses (Ayuk 2014; manufacturer's labeling).
Moderate deficiency (eg, serum magnesium 1 to 1.5 mg/dL):
IV: 2 to 4 g over 2 to 12 hours (Kraft 2005; Owen 2008; Todd 2009).
IM (50% concentration): 1 g every 6 hours for 4 doses (Ayuk 2014; manufacturer's labeling).
Severe deficiency (eg, serum magnesium <1 mg/dL):
IV: 4 to 8 g over 4 to 24 hours (Couture 2013; Kraft 2005).
Symptomatic patients (eg, tetany, arrhythmias, seizures) (excluding torsades de pointes and eclampsia/preeclampsia): Note: Continuous cardiac monitoring strongly recommended. Subsequent dosing may be based on serum magnesium levels assessed 6 to 12 hours after initial dosing. Repletion may take several days (Yu 2021).
IV:
Hemodynamically unstable: Initial: 1 to 2 g administered as a bolus over 2 to 15 minutes; may repeat as needed if patient remains unstable; once patient is stable, administer an additional 4 to 8 g over 12 to 24 hours (Yu 2021).
Hemodynamically stable: Initial: 1 to 2 g over 5 to 60 minutes, followed by an additional 4 to 8 g over 12 to 24 hours (Kraft 2005; Yu 2021).
Parenteral nutrition:
Note: Parenteral nutrition ordering requires advanced knowledge of nutrient and other metabolic requirements and should only be prescribed by clinicians trained in assessment and order writing for parenteral nutrition (ASPEN [Guenter 2015]).
Standard daily magnesium requirement: IV: Elemental magnesium 8 to 20 mEq (4 to 10 mmol) daily as component of parenteral nutrition; adjust daily dose based on serum magnesium and clinical considerations (ASPEN 2019).
Torsades de pointes (off-label use):
Polymorphic ventricular tachycardia (with pulse) associated with QT prolongation (torsades de pointes):
IV: 1 to 2 g (diluted in 50 to 100 mL D5W) over 15 minutes (range: 5 to 60 minutes). If no response or torsades de pointes recurs, may repeat dose up to a total of 4 g in 1 hour; may follow with a continuous IV infusion of 0.5 to 1 g/hour (AHA [Hazinski 2015]; AHA [Neumar 2010]; AHA [Panchal 2018]; Berul 2021).
Ventricular fibrillation/pulseless ventricular tachycardia associated with torsades de pointes: Note: Administer in conjunction with electrical cardioversion/defibrillation.
IV/intraosseous: 1 to 2 g (diluted in 10 mL D5W) administered as a bolus over ≥1 to 2 minutes; if ineffective, may repeat immediately (AHA [Neumar 2010]; AHA [Panchal 2018]; Berul 2021); use intraosseous route if IV not available. Some experts recommend a 2 g bolus initially (Pozner 2021) and repeat up to 2 additional 2 g bolus doses as needed; maximum total dose: 6 g (Berul 2021).
Eclampsia/preeclampsia, seizure prophylaxis and treatment: Severe renal impairment: IV: Initial: 4 to 6 g loading dose over 15 to 30 minutes, followed by 1 g/hour continuous infusion for at least 24 hours after delivery (ACOG 2020). Per the manufacturer, do not exceed 20 g during a 48-hour period. Note: Frequent monitoring of magnesium levels is important to avoid adverse effects in patients with renal impairment (ACOG 2020).
Constipation (alternative agent): Renal dysfunction: There are no dosage adjustments provided in the manufacturer's labeling; however, magnesium is renally excreted. Use with caution; accumulation in renal impairment may lead to magnesium toxicity.
Hypomagnesemia, treatment: Renal dysfunction: Reduce dose by 50% (Kraft 2005). Use with caution; monitor for hypermagnesemia; close monitoring is required.
No dosage adjustment necessary.
(For additional information see "Magnesium sulfate: Pediatric drug information")
Note: 1,000 mg of magnesium sulfate = 98.6 mg elemental magnesium = 8.12 mEq elemental magnesium = 4.06 mmol elemental magnesium. Serum magnesium is poor reflection of repletion 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.
Hypomagnesemia: Infants, Children, and Adolescents: Note: Dose depends on clinical condition and serum magnesium concentration.
Dose expressed as magnesium sulfate: IV, Intraosseous: 25 to 50 mg /kg/dose every 6 hours for 2 to 3 doses, then recheck serum concentration; maximum dose: 2,000 mg/dose (AAP [Shenoi 2020]; Kliegman 2020; PALS [Kleinman 2010]).
Dose expressed as elemental magnesium: IV: 2.5 to 5 mg/kg/dose every 6 hours for 2 to 3 doses (Kliegman 2020).
Constipation, occasional: Note: With OTC use, should not exceed recommended treatment duration (7 days) unless directed by health care provider.
Children 6 to <12 years: Oral: 1 to 2 level teaspoons of granules dissolved in 8 ounces of water; may repeat in 4 hours. Do not exceed 2 doses per day.
Children ≥12 years and Adolescents: Oral: 2 to 4 level teaspoons of granules dissolved in 8 ounces of water; may repeat in 4 hours. Do not exceed 2 doses per day.
Parenteral nutrition, maintenance magnesium requirement (ASPEN [Mirtallo 2004]): Dose expressed as elemental magnesium:
Infants and Children ≤50 kg: IV: 0.3 to 0.5 mEq/kg/day as an additive to parenteral nutrition solution.
Children >50 kg and Adolescents: IV: 10 to 30 mEq/day as an additive to parenteral nutrition solution.
Torsade de pointes or ventricular fibrillation/pulseless ventricular tachycardia associated with torsade de pointes: Dose expressed as magnesium sulfate:
Infants, Children, and Adolescents: IV, Intraosseous: 25 to 50 mg/kg/dose; maximum dose: 2,000 mg/dose (PALS [Kleinman 2010]).
Asthma, acute refractory exacerbation: Limited data available: Dose expressed as magnesium sulfate:
IV: Infants, Children, and Adolescents: 50 mg/kg/dose as a single dose (Becker 2019); usual dose range: 25 to 75 mg/kg/dose; maximum dose: 2,000 mg/dose; recommended as adjunctive therapy in severe acute asthma for patients who have life-threatening exacerbations and in those whose exacerbations remain in the severe category after 1 hour of intensive conventional therapy (AAP [Shenoi 2020]; GINA 2020; NAEPP 2007). Efficacy results have been variable in trials; some have shown significant improvement with single doses of 25 mg/kg/dose and 40 mg/kg/dose (Ciarallo 1996; Ciarallo 2000) while others found no statistically significant difference compared to placebo (Scarfone 2000). A pharmacokinetic modeling study of pediatric severe asthma suggested doses between 50 and 75 mg/kg to achieve concentrations within the hypothesized target range between 25 and 40 mg/L (Rower 2017).
Oral inhalation: Severe exacerbation: Limited data available: Children ≥2 years and Adolescents: Nebulized 150 mg isotonic magnesium sulfate mixed with albuterol and ipratropium every 20 minutes for 3 doses in the first hour of treatment to patients with severe acute asthma who did not respond to standard inhalation treatment (GINA 2020; Powell 2013). In a large randomized, placebo-controlled trial (n=508, including 252 who received magnesium sulfate treatment; ages: 2 to 16 years) improvement was statistically significant, but clinically significant changes were only observed in the most severe patients (SaO2 <92% with symptoms lasting <6 hours) (Powell 2013).
Hypomagnesemia: There are no dosage adjustments provided in the manufacturer's labeling; use with caution; monitor closely for hypermagnesemia.
No dosage adjustment necessary.
Refer to adult dosing.
Refer to indication-specific dosing for obesity-related information (may not be available for all indications).
Excipient information presented when available (limited, particularly for generics); consult specific product labeling. [DSC] = Discontinued product
Capsule, Oral:
M2 Magnesium: 100 mg
Magnacaps: 100 mg [DSC] [corn free, rye free, wheat free]
Generic: 70 mg
Granules, Oral:
Epsom Salt: (454 g, 1810 g)
GoodSense Epsom Salt: (454 g, 1810 g)
Solution, Injection:
Generic: 50% (10 mL, 20 mL)
Solution, Injection [preservative free]:
Generic: 50% (2 mL, 10 mL, 20 mL, 50 mL)
Solution, Intravenous:
Generic: 4 g/100 mL (100 mL); 1 g/100 mL (100 mL); 2 g/50 mL (50 mL); 20 g/500 mL (500 mL); 4 g/50 mL (50 mL); 40 g/1000 mL (1000 mL)
Solution, Intravenous [preservative free]:
Generic: 4 g/100 mL (100 mL); 1 g/100 mL (100 mL); 2 g/50 mL (50 mL); 4 g/50 mL (50 mL)
Yes
1 g of magnesium sulfate = 98.6 mg of elemental magnesium = 8.12 mEq of elemental magnesium = 4.06 mmol of elemental magnesium.
Magnesium sulfate 1% [10 mg/mL] in Dextrose 5% injection is equivalent to elemental magnesium 0.081 mEq/mL.
Magnesium sulfate 2% [20 mg/mL] in Dextrose 5% injection is equivalent to elemental magnesium 0.162 mEq/mL.
Magnesium sulfate 4% [40 mg/mL] in Water injection is equivalent to elemental magnesium 0.325 mEq/mL.
Magnesium sulfate 8% [80 mg/mL] in Water injection is equivalent to elemental magnesium 0.65 mEq/mL.
Magnesium sulfate 50% injection is equivalent to elemental magnesium 4 mEq/mL.
Magnesium sulfate USP is supplied as magnesium sulfate heptahydrate
Excipient information presented when available (limited, particularly for generics); consult specific product labeling. [DSC] = Discontinued product
Solution, Injection:
Generic: 20% (10 mL); 49.3% (500 mL); 50% (10 mL, 30 mL, 50 mL)
Solution, Intravenous:
Generic: 20 g/1000 mL in dextrose 5% ([DSC])
Injection: May be administered IM, intraosseous (IO), or IV.
IM: Adults: 50% concentration.
Eclampsia/preeclampsia: May mix with lidocaine 2% to reduce injection pain (ACOG 2019).
IV, intraosseous: Must be diluted to a ≤20% solution for IV infusion and may be administered IVP, IVPB, as a continuous IV infusion, or IO. When giving IV push, must dilute first and should generally not be given any faster than 150 mg/minute. In patients not in cardiac arrest, hypotension and asystole may occur with rapid administration. Refer to indication-specific infusion rates in dosing for detailed recommendations.
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.
Oral: Must dissolve granules prior to administration. When used as a laxative, the patient should drink a full 8 ounces of liquid following each dose. Lemon juice may be added to the initial solution to improve the taste. Note: Most effective when taken on an empty stomach.
Oral inhalation: Nebulization: Mix injectable solution with albuterol ± ipratropium and administer over 15 to 20 minutes (Powell 2013).
Parenteral:
IM: Infants and Children: Dilute prior to injection; in adults, doses are administered undiluted (50%) or diluted in a compatible fluid.
IV: Dilute in an appropriate fluid prior to administration. Rate of infusion dependent upon use:
Hypomagnesemia: Note: Rate should be slowed if patient experiences diaphoresis, flushing, or a warm sensation (Kliegman 2020).
Asymptomatic: In asymptomatic patients, a rate of ≤0.1 mEq/kg/hour of elemental magnesium (~12.5 mg/kg/hour magnesium sulfate) may be considered (in adults, the usual rate is ≤1,000 mg/hour of magnesium sulfate) (ASPEN [Corkins 2015]).
Urgent/emergent: Infuse slowly over 15 to 20 minutes (AAP [Shenoi 2020]).
Pulseless ventricular tachycardia (VT) associated with torsades: May administer as a bolus over several minutes (AAP [Shenoi 2020]; PALS [Kleinman 2010]).
VT with pulses associated with torsades: Infuse over 10 to 20 minutes; rapid infusion may cause hypotension (AAP [Shenoi 2020].
Asthma exacerbation (severe): Infuse over 15 to 60 minutes (AAP [Shenoi 2020]; GINA 2020).
Continuous IV infusion: After dilution, administer via an infusion pump.
Oral: Laxative for the relief of occasional constipation (OTC labeling).
Parenteral: Treatment and prevention of hypomagnesemia; prevention and treatment of seizures in severe preeclampsia or eclampsia; and treatment of cardiac arrhythmias (ventricular tachycardia/ventricular fibrillation) caused by hypomagnesemia.
Asthma (severe exacerbations); Fetal neuroprotection for imminent preterm birth (maternal administration); Torsades de pointes: Polymorphic ventricular tachycardia (with pulse) associated with QT prolongation (torsades de pointes) or ventricular fibrillation/pulseless ventricular tachycardia associated with torsades de pointes
Magnesium sulfate may be confused with manganese sulfate, morphine sulfate
MgSO4 is an error-prone abbreviation (mistaken as morphine sulfate)
The Institute for Safe Medication Practices (ISMP) includes this medication (IV formulation) among its list of drugs which have a heightened risk of causing significant patient harm when used in error.
The following adverse drug reactions and incidences are derived from product labeling unless otherwise specified. 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
Hypersensitivity to any component of the formulation; heart block (see Note); myocardial damage; IV use for preeclampsia/eclampsia during the 2 hours prior to delivery (see Note)
Note: Although the manufacturers' labeling for some IV formulations state use in preeclampsia/eclampsia during the 2 hours prior to (cesarean) delivery is contraindicated due to interaction with neuromuscular-blocking agents intraoperatively; stopping magnesium sulfate prior to cesarean delivery in these patients is not recommended and increases the risk of seizure. Instead, magnesium should be continued prior to and during the delivery (ACOG 2013). Additionally, the manufacturers' labeling for some IV formulations contraindicate the use of magnesium sulfate in the setting of heart block; however, the use of magnesium is appropriate in patients with serious conditions requiring magnesium therapy who either have mild degrees of heart block (eg, first degree) or more severe forms of heart block with a temporary or permanent cardiac pacemaker.
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) are 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 laxative, patients should consult a health care 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.
Multiple salt forms of magnesium exist; close attention must be paid to the salt form when ordering and administering magnesium; incorrect selection or substitution of one salt for another without proper dosage adjustment may result in serious over- or underdosing.
None known.
Alfacalcidol: May increase the serum concentration of Magnesium Salts. Management: Consider using a non-magnesium-containing antacid or phosphate-binding product in patients also receiving alfacalcidol. If magnesium-containing products must be used with alfacalcidol, serum magnesium concentrations should be monitored closely. Risk D: 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. Management: Separate administration of alpha-lipoic acid from that of any magnesium-containing compounds by several hours. If alpha-lipoic acid is given 30 minutes before breakfast, then administer oral magnesium-containing products at lunch or dinner. Risk D: Consider therapy modification
Baloxavir Marboxil: Polyvalent Cation Containing Products may decrease the serum concentration of Baloxavir Marboxil. Risk X: Avoid combination
Bictegravir: Polyvalent Cation Containing Products may decrease the serum concentration of Bictegravir. Management: Administer bictegravir under fasting conditions at least 2 hours before or 6 hours after polyvalent cation containing products. Coadministration of bictegravir with or 2 hours after most polyvalent cation products is not recommended. Risk D: Consider therapy modification
Bisphosphonate Derivatives: Polyvalent Cation Containing Products may decrease the serum concentration of Bisphosphonate Derivatives. Management: Avoid administration of oral medications containing polyvalent cations within: 2 hours before or after tiludronate/clodronate/etidronate; 60 minutes after oral ibandronate; or 30 minutes after alendronate/risedronate. Risk D: Consider therapy modification
Cabotegravir: Polyvalent Cation Containing Products may decrease the serum concentration of Cabotegravir. Management: Administer polyvalent cation containing products at least 2 hours before or 4 hours after oral cabotegravir. Risk D: Consider therapy modification
Calcitriol (Systemic): May increase the serum concentration of Magnesium Salts. Management: Consider using a non-magnesium-containing antacid or phosphate-binding product in patients also receiving calcitriol. If magnesium-containing products must be used with calcitriol, serum magnesium concentrations should be monitored closely. Risk D: Consider therapy modification
Calcium Channel Blockers (Dihydropyridine): Magnesium Sulfate may enhance the adverse/toxic effect of Calcium Channel Blockers (Dihydropyridine). Specifically, the risk of hypotension or muscle weakness may be increased. Risk C: 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. Risk X: Avoid combination
CNS Depressants: Magnesium Sulfate may enhance the CNS depressant effect of CNS Depressants. Risk C: Monitor therapy
Deferiprone: Polyvalent Cation Containing Products 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. Risk D: 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. Administer the dolutegravir/rilpivirine combination product at least 4 hours before or 6 hours after oral magnesium salts. Risk D: Consider therapy modification
Doxercalciferol: May enhance the hypermagnesemic effect of Magnesium Salts. Management: Consider using a non-magnesium-containing antacid or phosphate-binding product in patients also receiving doxercalciferol. If magnesium-containing products must be used with doxercalciferol, serum magnesium concentrations should be monitored closely. Risk D: Consider therapy modification
Eltrombopag: Polyvalent Cation Containing Products may decrease the serum concentration of Eltrombopag. Management: Administer eltrombopag at least 2 hours before or 4 hours after oral administration of any polyvalent cation containing product. Risk D: Consider therapy modification
Elvitegravir: Polyvalent Cation Containing Products may decrease the serum concentration of Elvitegravir. Management: Administer elvitegravir 2 hours before or 6 hours after the administration of polyvalent cation containing products. Risk D: 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 use of a magnesium-containing antacid. Monitor patients closely for evidence of reduced response to gabapentin therapy. Monitor for CNS depression if high dose IV/epidural magnesium sulfate is used. Risk D: 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. Risk D: 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. Risk D: Consider therapy modification
Neuromuscular-Blocking Agents: Magnesium Salts may enhance the neuromuscular-blocking effect of Neuromuscular-Blocking Agents. Risk C: Monitor therapy
PenicillAMINE: Polyvalent Cation Containing Products may decrease the serum concentration of PenicillAMINE. Management: Separate the administration of penicillamine and oral polyvalent cation containing products by at least 1 hour. Risk D: Consider therapy modification
Phosphate Supplements: Magnesium Salts may decrease the serum concentration of Phosphate Supplements. Management: Administer oral phosphate supplements as far apart from the administration of an oral magnesium salt as possible to minimize the significance of this interaction. Risk D: Consider therapy modification
Quinolones: Magnesium Salts may decrease the serum concentration of Quinolones. Management: Administer oral quinolones several hours before (4 h for moxi/pe/spar/enox-, 2 h for others) or after (8 h for moxi-, 6 h for cipro/dela-, 4 h for lome/pe/enox-, 3 h for gemi-, and 2 h for levo-, nor-, or ofloxacin or nalidixic acid) oral magnesium salts. Risk D: 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. Risk X: Avoid combination
Ritodrine: May enhance the adverse/toxic effect of Magnesium Sulfate. Risk C: Monitor therapy
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. Risk X: Avoid combination
Tetracyclines: Magnesium Salts may decrease the absorption of Tetracyclines. Only applicable to oral preparations of each agent. Management: Avoid coadministration of oral magnesium salts and oral tetracyclines. If coadministration cannot be avoided, administer oral magnesium at least 2 hours before, or 4 hours after, oral tetracyclines. Monitor for decreased tetracycline therapeutic effects. Risk D: Consider therapy modification
Trientine: Polyvalent Cation Containing Products may decrease the serum concentration of Trientine. Management: Avoid concomitant administration of trientine and oral products that contain polyvalent cations. If oral iron supplements are required, separate the administration by 2 hours. If other oral polyvalent cations are needed, separate administration by 1 hour. Risk D: Consider therapy modification
Increased alcohol intake can deplete magnesium stores (IOM, 1997).
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 to 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 preeclampsia or eclampsia (ACOG 2020). Magnesium sulfate may also be used prior to early preterm delivery for neuroprotection to reduce the risk of cerebral palsy (ACOG 2010; Reeves 2011); treatment may be of benefit when birth is anticipated before 32 weeks' gestation (ACOG 2016). 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 can be used up to 48 hours in women at risk of delivery within 7 days; however, it is not the preferred tocolytic (ACOG 2016). Magnesium sulfate injection may be used in conjunction with other tocolytics for neuroprotection; however, an increased risk of maternal complications may be observed when used in combination with some tocolytic agents (ACOG 2016).
Magnesium is present in breast milk.
When magnesium sulfate is used in the intrapartum management of eclampsia, breast milk concentrations are generally increased for only ~24 hours after the end of treatment. In one study, this amounted to an increase of only 1.5 mg of magnesium to the breastfed infant on the first day after maternal therapy was stopped (Cruikshank 1982; Idama 1998).
Magnesium is endogenous to breast milk; concentrations remain constant during the first year of lactation and are not influenced by dietary intake under normal conditions (IOM 1997). Milk concentrations of magnesium are variable between females, but are generally consistent within a given mother (Dórea 2000).
Magnesium requirements are the same in breastfeeding and nonbreastfeeding females (IOM 1997). Although the manufacturer recommends that caution be used if administered to breastfeeding females; magnesium sulfate when used for the prevention of seizures is considered compatible with breastfeeding (WHO 2002).
Whole grains, legumes and dark-green leafy vegetables are dietary sources of magnesium (IOM 1997).
Adequate intake (AI) (elemental magnesium) (IOM 1997):
1 to 6 months: 30 mg daily
7 to 12 months: 75 mg daily
Dietary recommended daily allowance (RDA) (elemental magnesium) (IOM 1997):
1 to 3 years: 80 mg daily
4 to 8 years: 130 mg daily
9 to 13 years: 240 mg daily
14 to 18 years:
Females: 360 mg daily
Pregnancy: 400 mg daily
Lactation: 360 mg daily
Males: 410 mg daily
19 to 30 years:
Females: 310 mg daily
Pregnancy: 350 mg daily
Lactation: 310 mg daily
Males: 400 mg daily
≥31 years:
Females: 320 mg daily
Pregnancy: 360 mg daily
Lactation: 320 mg daily
Males: 420 mg daily
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, respiration, deep tendon reflexes, level of consciousness, fetal heart rate, maternal uterine activity, renal function. Monitor magnesium concentrations every 4 hours in patients with renal dysfunction (every 2 hours if serum magnesium is >8 mEq/L (ACOG 2020).
Note: Reference ranges may vary depending on the laboratory.
Magnesium serum concentration: Adults: 1.5 to 2.5 mg/dL.
Eclampsia/preeclampsia therapeutic range: 5 to 9 mg/dL (ACOG 2020).
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.
Onset of action: Antiseizure medication: IM: 1 hour; IV: Immediate; Laxative: Oral: 0.5 to 6 hours
Duration of antiseizure activity: IM: 3 to 4 hours; IV: 30 minutes
Absorption: Oral: Slow and poor (approximately one-third absorbed)
Distribution: Bone (50% to 60%); extracellular fluid (1% to 2%) (IOM 1997)
Protein binding: 30%, to albumin
Excretion: Urine (as magnesium); feces (as unabsorbed drug)
Solution (Magnesium Sulfate in D5W Intravenous)
1GM/100ML 5% (per mL): $0.04 - $0.10
Solution (Magnesium Sulfate Injection)
50% (per mL): $0.72 - $1.04
Solution (Magnesium Sulfate Intravenous)
2 gm/50 mL (per mL): $0.16 - $0.40
4 g/100 mL (per mL): $0.05 - $0.11
4 gm/50 mL (per mL): $0.11 - $0.19
20 g/500 mL (per mL): $0.01
40GM/1000ML (per mL): $0.01
Disclaimer: A representative AWP (Average Wholesale Price) price or price range is provided as reference price only. A range is provided when more than one manufacturer's AWP price is available and uses the low and high price reported by the manufacturers to determine the range. The pricing data should be used for benchmarking purposes only, and as such should not be used alone to set or adjudicate any prices for reimbursement or purchasing functions or considered to be an exact price for a single product and/or manufacturer. Medi-Span expressly disclaims all warranties of any kind or nature, whether express or implied, and assumes no liability with respect to accuracy of price or price range data published in its solutions. In no event shall Medi-Span be liable for special, indirect, incidental, or consequential damages arising from use of price or price range data. Pricing data is updated monthly.
