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Magnesium Sulfate

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

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.

Pharmacokinetics
Absorption:
Approximately 1% to 2% of total body magnesium is in the extracellular fluid space; 30% bound to albumin. Excreted solely by the kidneys at a rate proportional to the serum concentration and glomerular filtration. Immediate (IV, when used as an anticonvulsant); 1 h (IM). 30 min (IV, when used as an anticonvulsant); 3 to 4 h (IM).
Special Populations

Indications and Usage

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 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.
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
Barium P soning Adults
IV 1 to 2 g.

Cerebr

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

Paroxysmal Atrial Tachycardia Adults
IV 3 to 4 g (30 to 40 mL of a 10% solutio ) over 30 sec with extreme caution. Use only if simpler ave 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 ciated 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 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)

Renal impairment
The dose should be lower and frequent serum magnesium levels must be obtained. Consider
reducing

General Advice

administration only. Not for intradermal, subcutaneous, or intra-arterial administration. IM administration is painful; avoid if possible. se 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 e • 50% solution may be administered undiluted to adults if given by deep IM injection. Rotate injection sites to reduce tissue irritation. um 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. • 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), al alkali hydroxides, arsenates, barium, calcium, clindamycin, heavy metals, hydrocortisone sodium succinate, phosphates, polymyxin B, procaine, salicylates, streptomycin, strontium, tartrates, tetracycline, tobramycin.
Storage/Stability

ct from freezing. Discard any unused solution. Unused portions of the the container should be discarded within 24 h of initial use.
Drug Interactions

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 th admi
nistration 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.
uromuscular blocking agent dose as needed. Be prepared to provide life support.
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
cillam e effects (oral magnesium). No special precautions are needed.
Tetracyclines
Decreased absorption of tetracyclines (oral magnesium). Separate the administration times by 3
to

Adverse Reactions
Cardiovascular
Cardiac arre
ression; circulatory collapse; hypotension.
CNS
CNS depression; depressed reflexes; flaccid paralysis.

Metabolic
Hypermagnesemia; hypocalcemia with signs of tetany.

Respiratory
Respiratory depression; respiratory paralysis.

Miscellan

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.
May requ re reduced dosage because of renal impairment.

Rena
Use with caution; renal impairment may lead to magnesium intoxication. Aluminum toxicit Some of these products may contain aluminum that cluding premature neonates, who receive parenteral levels of aluminum at more than 4 ate 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.

Flushi

Administer with caution if flushing and sweating occurs.

Overdosage

Symptoms
Decreased deep tendon reflexes, disappearance of patellar reflex, ECG changes (ie, prolonged
prolonged QRS complex, prolonged QT interval), heart block, hypotension, atient Inf
ormation
• Advise patient that medication will be prepared and administered by a health care ealth care provider if drowsiness, muscle weakness, sweating, • Advise patient to mix granules in at least a half glass of water before swallowing and to atient to mix with ice chips or flavor with lemon or • 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- rm laxative u lead to dehydration and electrolyte imbalance. • Advise patient to discontinue use and notify heal unrelieved constipation, rectal bleeding, symptoms of electrolyte imbalance (eg, muscle cramps or pain, weakness, dizziness). Copyright 2009 Wolters Kluwer Health.

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