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Magnesium Sulfate

Pronunciation

Pronunciation: mag-NEE-zee-um SUL-fate
Class: Mineral, Anticonvulsant, Saline Laxative

Trade Names

Epsom Salt
- Granules, oral

Magnesium Sulfate
- Injection, solution 4% (elemental magnesium 0.325 mEq/mL)
- Injection, solution, concentrate 8% (elemental magnesium 0.65 mEq/mL)
- Injection, solution, concentrate 50% (elemental magnesium 4 mEq/mL)

Magnesium Sulfate in Dextrose 5%
- Injection, solution 1% (elemental magnesium 0.081 mEq/mL)
- Injection, solution 2% (elemental magnesium 0.162 mEq/mL)

Pharmacology

Magnesium is an important activator of many enzyme systems, and deficits are accompanied by a variety of functional disturbances. Magnesium has CNS depressant effects; it prevents/controls seizures by blocking neuromuscular transmission and decreasing the amount of acetylcholine liberated at end plate by motor nerve impulse. Orally, it attracts/retains water in intestinal lumen, thereby increasing intraluminal pressure and inducing the urge to defecate.

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Pharmacokinetics

Absorption

Immediately absorbed (IV).

Distribution

Approximately 1% to 2% of total body magnesium is in the extracellular fluid space; 30% bound to albumin.

Metabolism

Magnesium is not metabolized.

Elimination

Excreted solely by the kidneys at a rate proportional to the serum concentration and glomerular filtration.

Onset

Immediate (IV, when used as an anticonvulsant); 1 h (IM).

Duration

30 min (IV, when used as an anticonvulsant); 3 to 4 h (IM).

Special Populations

Renal Function Impairment

No data available.

Hepatic Function Impairment

No data available.

Indications and Usage

Parenteral

Seizure prevention and control in severe preeclampsia or eclampsia; replacement therapy in magnesium deficiency, especially in acute hypomagnesemia accompanied by signs of tetany similar to those observed in hypocalcemia; corrects or prevents hypomagnesemia by addition to TPN admixture; control hypertension, encephalopathy, and convulsions in children with acute nephritis.

Oral

Laxative.

Unlabeled Uses

Treatment of acute exacerbation of severe asthma; treatment of torsades de pointes; paroxysmal atrial tachycardia; cerebral edema; barium poisoning.

Contraindications

Toxemia of pregnancy during 2 h preceding delivery.

Dosage and Administration

Hyperalimentation
Adults

TPN 5 to 8 mEq of magnesium per 1 L of TPN solution. Typical daily intakes range from 10 to 24 mEq/day.

Children

TPN 0.25 to 0.6 mEq/kg/day.

Hypomagnesemia
Adults Mild hypomagnesemia

IM 1 g (2 mL of undiluted 50% solution) injected every 6 h for 4 doses.

Severe hypomagnesemia

IV / IM As much as 246 mg/kg (0.5 mL/kg of the undiluted 50% solution) may be given within a period of 4 h if necessary. Alternatively, 5 g (10 mL) can be added to 1 L of dextrose 5% injection or sodium chloride 0.9% injection for slow IV infusion over a 3-h period. According to American Heart Association (AHA) guidelines, the recommended dosage is 1 to 2 g IV over 5 to 60 min. If seizures are present, give 2 g IV over 10 min. Use caution so as not to exceed the renal excretion capacity.

Laxative

Usually a one-time dose.

Adults

PO 10 to 15 g.

Children

PO 5 to 10 g.

Nephritic Seizures
Children

IM 20 to 40 mg/kg (0.1 to 0.2 mL/kg of a 20% solution) as needed to control seizures.

Seizures in Eclampsia/Preeclampsia

IM / IV 10 to 14 g (as a combination of 4 to 5 g of undiluted 50% solution in each buttock and 4 to 5 g IV in 250 mL of dextrose 5% injection or sodium chloride 0.9% injection, or 4 g of magnesium/dextrose 5% injection premixed solution). Alternatively, the initial IV dose of 4 g may be given by diluting the 50% solution to a 10% or 20% solution and the diluted fluid (40 mL of a 10% solution or 20 mL of a 20% solution) may be injected over 3 to 4 minutes. After the initial dose, 1 to 2 g/h by constant IV infusion or IM doses of 4 to 5 g of undiluted 50% solution every 4 h injected into alternate buttocks as needed (max, 30 to 40 g per 24 h and less in anuric patients). Therapy should continue until paroxysms cease. According to American College of Obstetricians and Gynecologists guidelines, the initial dosage is 4 to 6 g (diluted in 100 mL) given IV over 15 to 20 min, followed by a maintenance dosage of 2 g/h continuous IV infusion.

Off-Label Uses
Asthma (life-threatening) Adults

IV 1.2 to 2 g over 20 min according to AHA/American College of Cardiology (ACC) guidelines.

Children

IV 25 to 75 mg/kg (max dose, 2 g) over 20 min every 4 to 6 hours for 3 or 4 doses; repeat as needed.

Barium Poisoning Adults

IV 1 to 2 g.

Cerebral Edema Adults

IV 2.5 g (25 mL of a 10% solution).

Hypomagnesemia Children

IV / intraosseous 25 to 50 mg/kg (max dose, 2 g) over 10 to 20 min every 4 to 6 h for 3 or 4 doses; repeat as needed.

Paroxysmal Atrial Tachycardia Adults

IV 3 to 4 g (30 to 40 mL of a 10% solution) over 30 sec with extreme caution. Use only if simpler measures have failed and there is no evidence of myocardial damage.

Torsades de Pointes Adults

IV The following recommendations are according to AHA/ACC guidelines. If torsades de pointes is associated with cardiac arrest, 1 to 2 g (diluted in 10 mL of dextrose 5% injection) administered IV/intraosseous over 5 to 20 min. If torsades de pointes is intermittent and not associated with cardiac arrest, dilute 1 to 2 g in 50 to 100 mL of dextrose 5% injection and administer over 5 to 60 min.

Children

IV According to AHA/ACC guidelines, the dosage is 25 to 50 mg/kg (max dose, 2 g) IV/intraosseous over several min.

Renal impairment

The dose should be lower and frequent serum magnesium levels must be obtained. Consider reducing the dose by 50% (max adults, 20 g per 48 h).

General Advice

  • Injection
  • For IM or IV administration only. Not for intradermal, subcutaneous, or intra-arterial administration. IM administration is painful; avoid if possible.
  • IV bolus may cause flushing, sweating, and warm sensation; avoid if possible.
  • Rate of IV injection should generally not exceed 150 mg/min (1.5 mL of a 10% concentration or 7.5 mL of a 2% concentration or its equivalent), except in severe eclampsia with seizures.
  • 50% solution may be administered undiluted to adults if given by deep IM injection. Rotate injection sites to reduce tissue irritation.
  • 50% solution must be diluted with sodium chloride 0.9% injection or dextrose 5% injection to a concentration of 20% or less before IV administration or IM administration in infants and children.
  • When administering via IV route, use infusion pump. Deliver in separate line and do not mix with other IV drugs unless compatibility has been established.
  • Have an IV calcium preparation at hand as an antidote.
  • Prior to repeat doses, test for knee-jerk reflexes. If they are absent, no additional magnesium should be given until reflexes return.
  • Incompatibilities: alcohol (in high concentrations), alkali carbonates and bicarbonates, alkali hydroxides, arsenates, barium, calcium, clindamycin, heavy metals, hydrocortisone sodium succinate, phosphates, polymyxin B, procaine, salicylates, streptomycin, strontium, tartrates, tetracycline, tobramycin.

Storage/Stability

Store at 68° to 77°F. Protect from freezing. Discard any unused solution. Unused portions of the undiluted 50% solution in the container should be discarded within 24 h of initial use.

Drug Interactions

Alcohol, aminoglycosides, amphotericin B, cisplatin, cyclosporine, digitalis, diuretics

Drug-induced renal losses of magnesium can occur. Use with caution and closely monitor magnesium concentrations.

Chloroquine, eltrombopag

Oral magnesium sulfate may decrease the absorption and clinical effect of chloroquine or eltrombopag. Separate the administration times of chloroquine and oral magnesium sulfate by 2 to 4 h. Higher doses of chloroquine may be needed. Separate the administration times of eltrombopag and oral magnesium sulfate by at least 4 h.

Neuromuscular blocking agents

Potentiation of neuromuscular blockade; use with caution. Monitor for respiratory depression. Adjust the neuromuscular blocking agent dose as needed. Be prepared to provide life support.

Nifedipine

The risk of neuromuscular blockade and hypotension may be increased. Closely monitor the clinical response. Be prepared to provide supportive treatment or to discontinue one or both drugs if needed.

Nitrofurantoin

Decreased absorption of nitrofurantoin (oral magnesium). Separate the administration times by as much as possible.

Penicillamine

Reduced penicillamine effects (oral magnesium). No special precautions are needed.

Tetracyclines

Decreased absorption of tetracyclines (oral magnesium). Separate the administration times by 3 to 4 h.

Adverse Reactions

Cardiovascular

Cardiac arrest; cardiac depression; circulatory collapse; hypotension.

CNS

CNS depression; depressed reflexes; flaccid paralysis.

Metabolic

Hypermagnesemia; hypocalcemia with signs of tetany.

Respiratory

Respiratory depression; respiratory paralysis.

Miscellaneous

Flushing; hypothermia; sweating.

Precautions

Monitor

Monitor serum magnesium levels and the patient's clinical status to guide need for continued dosage. Normal serum concentration is 1.5 to 2.5 or 3 mEq/mL. Effective anticonvulsant serum levels range from 2.5 or 3 to 7.5 mEq/L (6 mg per 100 mL). Monitor levels hourly for patients with severe hypomagnesemia until they reach 1.5 mEq/mL, then every 6 to 12 h for the next 24 h. Once stable, obtain the serum concentration daily. Carefully observe respiration and BP during and after administration of IV magnesium. Urine output should be maintained at 100 mL every 4 h. Clinical indications of a safe dosage regimen include the presence of the patellar reflex (knee-jerk) and absence of respiratory depression (approximately 16 or more breaths per minute). When repeated doses of the drug are given parenterally, knee-jerk reflexes should be tested before each dose; if they are absent, no additional magnesium should be given until they return. The strength of the deep tendon reflexes begins to diminish when magnesium levels exceed 4 mEq/L. Reflexes may be absent at magnesium 10 mEq/L, where respiratory paralysis is a potential hazard.


Pregnancy

Category A / Category C , depending on manufacturer.

Lactation

Excreted. The American Academy of Pediatrics classifies magnesium as compatible with breast-feeding.

Elderly

May require reduced dosage because of renal impairment.

Renal Function

Use with caution; renal impairment may lead to magnesium intoxication.

Aluminum toxicity

Some of these products may contain aluminum that may be toxic. Patients with impaired kidney function, including premature neonates, who receive parenteral levels of aluminum at more than 4 to 5 mcg/kg/day accumulate aluminum at levels associated with CNS and bone toxicity. Tissue loading may occur at even lower rates of administration.

Eclampsia

Use IV form only for immediate control of life-threatening convulsions.

Flushing/Sweating

Administer with caution if flushing and sweating occurs.

Overdosage

Symptoms

Decreased deep tendon reflexes, disappearance of patellar reflex, ECG changes (ie, prolonged PR interval, prolonged QRS complex, prolonged QT interval), heart block, hypotension, respiratory paralysis.

Patient Information

  • Injection
  • Advise patient that medication will be prepared and administered by a health care provider in a hospital setting.
  • Instruct patient to notify health care provider if drowsiness, muscle weakness, sweating, flushing, or dizziness occurs.
  • Oral
  • Advise patient to mix granules in at least a half glass of water before swallowing and to follow with a full glass of water. Advise patient to mix with ice chips or flavor with lemon or orange juice to make more palatable.
  • Educate patient regarding other measures that may help prevent constipation (eg, adequate fluid intake, dietary fiber, regular exercise).
  • Caution patient that drug is for short-term laxative use only and that prolonged use can lead to dehydration and electrolyte imbalance.
  • Advise patient to discontinue use and notify health care provider of the following: unrelieved constipation, rectal bleeding, symptoms of electrolyte imbalance (eg, muscle cramps or pain, weakness, dizziness).

Copyright © 2009 Wolters Kluwer Health.

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