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In the treatment of mild magnesium deficiency, the usual adult dose is 1 g, equivalent to 8.12 mEq of magnesium (2 mL of the 50% solution) injected intramuscularly every six hours for four doses (equivalent to a total of 32.5 mEq of magnesium per 24 hours).
For severe hypomagnesemia, as much as 250 mg (approximately 2 mEq) per kg of body weight (0.5 mL of the 50% solution) may be given intramuscularly within a period of four hours if necessary. Alternatively, 5 g (approximately 40 mEq) can be added to one liter of 5% Dextrose Injection, USP or 0.9% Sodium Chloride Injection, USP for slow intravenous infusion over a three-hour period. In the treatment of deficiency states, caution must be observed to prevent exceeding the renal excretory capacity.
Hyperalimentation
Dosing Information
In total parenteral nutrition, maintenance requirements for magnesium are not precisely known.
The maintenance dose used in adults ranges from 8 to 24 mEq (1 to 3 g) daily.
Pre-Eclampsia or Eclampsia
Dosing Information
In severe pre-eclampsia or eclampsia, the total initial dose is 10 to 14 g of magnesium sulfate. Intravenously, a dose of 4 to 5 g in 250 mL of 5% Dextrose Injection, USP or 0.9% Sodium Chloride Injection, USP may be infused. Simultaneously, intramuscular doses of up to 10 g (5 g or 10 mL of the undiluted 50% solution in each buttock) are given. Alternatively, the initial intravenous dose of 4 g may be given by diluting the 50% solution to a 10 or 20% concentration; the diluted fluid (40 mL of a 10% solution or 20 mL of a 20% solution) may then be injected intravenously over a period of three to four minutes. Subsequently, 4 to 5 g (8 to 10 mL of the 50% solution) are injected intramuscularly into alternate buttocks every four hours as needed, depending on the continuing presence of the patellar reflex and adequate respiratory function. Alternatively, after the initial I.V. dose, some clinicians administer 1 to 2 g/hour by constant I.V. infusion. Therapy should continue until paroxysms cease. A serum magnesium level of 6 mg/100 mL is considered optimal for control of seizures. A total daily (24 hr) dose of 30 to 40 g should not be exceeded. In the presence of severe renal insufficiency, the maximum dosage of magnesium sulfate is 20 grams/48 hours and frequent serum magnesium concentrations must be obtained. Continuous use of magnesium sulfate in pregnancy beyond 5 to 7 days can cause fetal abnormalities.
Barium Poisoning
Dosing Information
1–2 g intravenous
Seizures Associated with Epilepsy, Glomerulonephritis or Hypothyroidism
Dosing Information
1 g IV or IM
Paroxysmal Atrial Tachycardia
Magnesium should be used only if simpler measures have failed and there is no evidence of myocardial damage.
Dosing Information
3–4 g (30 to 40 mL of a 10% solution) administered IV over 30 seconds with extreme caution.
Cerebral Edema
Dosing Information
2.5 g (25 mL of a 10% solution) intravenous
Off-Label Use and Dosage (Adult)
Guideline-Supported Use
There is limited information regarding Off-Label Guideline-Supported Use of Magnesium sulfate (injection) in adult patients.
Non–Guideline-Supported Use
There is limited information regarding Off-Label Non–Guideline-Supported Use of Magnesium sulfate (injection) in adult patients.
Pediatric Indications and Dosage
FDA-Labeled Indications and Dosage (Pediatric)
Hyperalimentation
Dosing Information
For infants, the dosing range is 2 to 10 mEq (0.25 to 1.25 g) daily.
Off-Label Use and Dosage (Pediatric)
Guideline-Supported Use
There is limited information regarding Off-Label Guideline-Supported Use of Magnesium sulfate (injection) in pediatric patients.
Non–Guideline-Supported Use
There is limited information regarding Off-Label Non–Guideline-Supported Use of Magnesium sulfate (injection) in pediatric patients.
Contraindications
Parenteral administration of the drug is contraindicated in patients with heart block or myocardial damage.
Warnings
Fetal Harm
Continuous administration of magnesium sulfate beyond 5 to 7 days to pregnant women can lead to hypocalcemia and bone abnormalities in the developing fetus. These bone abnormalities include skeletal demineralization and osteopenia. In addition, cases of neonatal fracture have been reported. The shortest duration of treatment that can lead to fetal harm is not known. Magnesium sulfate should be used during pregnancy only if clearly needed. If magnesium sulfate is given for treatment of preterm labor, the woman should be informed that the efficacy and safety of such use have not been established and that use of magnesium sulfate beyond 5 to 7 days may cause fetal abnormalities.
Aluminum Toxicity
This product contains aluminum that may be toxic. Aluminum may reach toxic levels with prolonged parenteral administration if kidney function is impaired. Premature neonates are particularly at risk because their kidneys are immature, and they require large amounts of calcium and phosphate solutions, which contain aluminum.
Research indicates that patients with impaired kidney function, including premature neonates, who receive parenteral levels of aluminum at greater than 4 to 5 mcg/kg/day accumulate aluminum at levels associated with central nervous system and bone toxicity. Tissue loading may occur at even lower rates of administration.
Parenteral use in the presence of renal insufficiency may lead to magnesium intoxication. IV use in the eclampsia should be reserved for immediate control of life-threatening convulsions.
Precautions
Laboratory Tests
Magnesium sulfate injection should not be given unless hypomagnesemia has been confirmed and the serum concentration of magnesium is monitored. The normal serum level is 1.5 to 2.5 mEq/L.
Adverse Reactions
Clinical Trials Experience
There is limited information regarding Clinical Trial Experience of Magnesium sulfate (injection) in the drug label.
Postmarketing Experience
The adverse effects of parenterally administered magnesium usually are the result of magnesium intoxication. These include flushing, sweating, hypotension, depressed reflexes, flaccid paralysis, hypothermia, circulatory collapse, cardiac and central nervous system depression proceeding to respiratory paralysis. Hypocalcemia with signs of tetany secondary to magnesium sulfate therapy for eclampsia has been reported.
Drug Interactions
CNS Depressants
When barbiturates, narcotics or other hypnotics (or systemic anesthetics), or other CNS depressants are to be given in conjunction with magnesium, their dosage should be adjusted with caution because of additive CNS depressant effects of magnesium. CNS depression and peripheral transmission defects produced by magnesium may be antagonized by calcium.
Neuromuscular Blocking Agents
Excessive neuromuscular block has occurred in patients receiving parenteral magnesium sulfate and a neuromuscular blocking agent; these drugs should be administered concomitantly with caution.
Cardiac Glycosides
Magnesium sulfate should be administered with extreme caution in digitalized patients, because serious changes in cardiac conduction which can result in heart block may occur if administration of calcium is required to treat magnesium toxicity.
Magnesium sulfate can cause fetal abnormalities when administered beyond 5 to 7 days to pregnant women. There are retrospective epidemiological studies and case reports documenting fetal abnormalities such as hypocalcemia, skeletal demineralization, osteopenia and other skeletal abnormalities with continuous maternal administration of magnesium sulfate for more than 5 to 7 days.1-10 Magnesium sulfate injection should be used during pregnancy only if clearly needed. If this drug is used during pregnancy, the woman should be apprised of the potential harm to the fetus.
Nonteratogenic Effects
When administered by continuous intravenous infusion (especially for more than 24 hours preceding delivery) to control convulsions in a toxemic woman, the newborn may show signs of magnesium toxicity, including neuromuscular or respiratory depression
Australian Drug Evaluation Committee (ADEC) Pregnancy Category
There is no Australian Drug Evaluation Committee (ADEC) guidance on usage of Magnesium sulfate (injection) in women who are pregnant.
Labor and Delivery
Continuous administration of magnesium sulfate is an unapproved treatment for preterm labor. The safety and efficacy of such use have not been established. The administration of magnesium sulfate outside of its approved indication in pregnant women should be by trained obstetrical personnel in a hospital setting with appropriate obstetrical care facilities.
Nursing Mothers
Since magnesium is distributed into milk during parenteral magnesium sulfate administration, the drug should be used with caution in nursing women.
Pediatric Use
There is no FDA guidance on the use of Magnesium sulfate (injection) with respect to pediatric patients.
Geriatic Use
Geriatric patients often require reduced dosage because of impaired renal function. In patients with severe impairment, dosage should not exceed 20 g in 48 hours. Serum magnesium should be monitored in such patients.
Gender
There is no FDA guidance on the use of Magnesium sulfate (injection) with respect to specific gender populations.
Race
There is no FDA guidance on the use of Magnesium sulfate (injection) with respect to specific racial populations.
Renal Impairment
There is no FDA guidance on the use of Magnesium sulfate (injection) in patients with renal impairment.
Hepatic Impairment
There is no FDA guidance on the use of Magnesium sulfate (injection) in patients with hepatic impairment.
Females of Reproductive Potential and Males
There is no FDA guidance on the use of Magnesium sulfate (injection) in women of reproductive potentials and males.
Immunocompromised Patients
There is no FDA guidance one the use of Magnesium sulfate (injection) in patients who are immunocompromised.
Administration and Monitoring
Administration
Intravenous
Monitoring
Because magnesium is removed from the body solely by the kidneys, the drug should be used with caution in patients with renal impairment. Urine output should be maintained at a level of 100 mL or more during the four hours preceding each dose. Monitoring serum magnesium levels and the patient’s clinical status is essential to avoid the consequences of overdosage in toxemia.
IV Compatibility
Magnesium sulfate in solution may result in a precipitate formation when mixed with solutions containing:
Alcohol (in high concentrations)
Alkali carbonates and bicarbonates
Alkali hydroxides
Arsenates
Barium
Calcium
Clindamycin phosphate
Heavy metals
Hydrocortisone sodium succinate
Phosphates
Polymixin B sulfate
Procaine hydrochloride
Salicylates
Strontium tartrates
The potential incompatibility will often be influenced by the changes in the concentration of reactants and the pH of the solutions.
It has been reported that magnesium may reduce the antibiotic activity of streptomycin, tetracycline and tobramycin when given together.
Parenteral drug products should be inspected visually for particulate matter and discoloration prior to administration, whenever solution and container permit.
Overdosage
Acute Overdose
Signs and Symptoms
Magnesium intoxication is manifested by a sharp drop in blood pressure and respiratory paralysis. Disappearance of the patellar reflex is a useful clinical sign to detect the onset of magnesium intoxication.
Management
In the event of overdosage, artificial ventilation must be provided until a calcium salt can be injected intravenously to antagonize the effects of magnesium.
Artificial respiration is often required. Intravenous calcium, 10 to 20 mL of a 5% solution (diluted if desirable with isotonic sodium chloride for injection) is used to counteract effects of hypermagnesemia. Subcutaneous physostigmine, 0.5 to 1 mg may be helpful.
Hypermagnesemia in the newborn may require resuscitation and assisted ventilation via endotracheal intubation or intermittent positive pressure ventilation as well as intravenous calcium.
Chronic Overdose
There is limited information regarding Chronic Overdose of Magnesium sulfate (injection) in the drug label.
Pharmacology
There is limited information regarding Magnesium sulfate (injection) Pharmacology in the drug label.
Mechanism of Action
Magnesium (Mg++) is an important cofactor for enzymatic reactions and plays an important role in neurochemical transmission and muscular excitability.
As a nutritional adjunct in hyperalimentation, the precise mechanism of action for magnesium is uncertain. Early symptoms of hypomagnesemia (less than 1.5 mEq/liter) may develop as early as three to four days or within weeks.
Predominant deficiency effects are neurological, e.g., muscle irritability, clonic twitching and tremors. Hypocalcemia and hypokalemia often follow low serum levels of magnesium. While there are large stores of magnesium present intracellularly and in the bones of adults, these stores often are not mobilized sufficiently to maintain plasma levels. Parenteral magnesium therapy repairs the plasma deficit and causes deficiency symptoms and signs to cease.
Magnesium prevents or controls convulsions by blocking neuromuscular transmission and decreasing the amount of acetylcholine liberated at the end plate by the motor nerve impulse. Magnesium is said to have a depressant effect on the central nervous system (CNS), but it does not adversely affect the woman, fetus or neonate when used as directed in eclampsia or pre-eclampsia. Normal plasma magnesium levels range from 1.5 to 2.5 mEq/liter.
Structure
Magnesium Sulfate Injection, USP is a sterile solution of magnesium sulfate heptahydrate in Water for Injection, USP administered by the intravenous or intramuscular routes as an electrolyte replenisher or anticonvulsant. Must be diluted before I.V. use. May contain sulfuric acid and/or sodium hydroxide for pH adjustment. The pH is 6.0 (5.5 to 7.0). The 50% concentration has an osmolarity of 4.06 mOsmol/mL (calc.).
The solution contains no bacteriostat, antimicrobial agent or added buffer (except for pH adjustment) and is intended only for use as a single-dose injection. When smaller doses are required the unused portion should be discarded with the entire unit.
Magnesium Sulfate, USP heptahydrate is chemically designated MgSO4 • 7H2O with molecular weight of 246.48 and occurs as colorless crystals or white powder freely soluble in water.
The plastic syringe is molded from a specially formulated polypropylene. Water permeates from inside the container at an extremely slow rate which will have an insignificant effect on solution concentration over the expected shelf life. Solutions in contact with the plastic container may leach out certain chemical components from the plastic in very small amounts; however, biological testing was supportive of the safety of the syringe material.
Pharmacodynamics
As plasma magnesium rises above 4 mEq/liter, the deep tendon reflexes are first decreased and then disappear as the plasma level approaches 10 mEq/liter. At this level respiratory paralysis may occur. Heart block also may occur at this or lower plasma levels of magnesium. Serum magnesium concentrations in excess of 12 mEq/L may be fatal.
Magnesium acts peripherally to produce vasodilation. With low doses only flushing and sweating occur, but larger doses cause lowering of blood pressure. The central and peripheral effects of magnesium poisoning are antagonized to some extent by intravenous administration of calcium.
Pharmacokinetics
With intravenous administration the onset of anticonvulsant action is immediate and lasts about 30 minutes. Following intramuscular administration the onset of action occurs in about one hour and persists for three to four hours. Effective anticonvulsant serum levels range from 2.5 to 7.5 mEq/liter. Magnesium is excreted solely by the kidneys at a rate proportional to the plasma concentration and glomerular filtration.
Nonclinical Toxicology
There is limited information regarding Nonclinical Toxicology of Magnesium sulfate (injection) in the drug label.
Clinical Studies
There is limited information regarding Clinical Studies of Magnesium sulfate (injection) in the drug label.
How Supplied
Magnesium Sulfate Injection, USP is supplied in single-dose containers as follows:
There is limited information regarding Patient Counseling Information of Magnesium sulfate (injection) in the drug label.
Precautions with Alcohol
Alcohol-Magnesium sulfate (injection) interaction has not been established. Talk to your doctor about the effects of taking alcohol with this medication.
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