Magnesium Sulfate

For Intravenous Use Only

Rx only

Magnesium Sulfate in Water for Injection is a sterile, nonpyrogenic solution of magnesium sulfate heptahydrate in water for injection.  May contain sulfuric acid and/or sodium hydroxide for pH adjustment.  The pH is 4.5 (3.5 to 6.5).  It is available in 4% and 8% concentrations.  See HOW SUPPLIED section for the content and characteristics of available dosage forms and sizes.

Magnesium sulfate, USP heptahydrate is chemically designated MgSO ₄ • 7H ₂O, colorless crystals or white powder freely soluble in water.

Water for injection, USP is chemically designated H ₂O.

The flexible container is fabricated from a specially formulated non-plasticized, film containing polypropylene and thermoplastic elastomers ( freeflex ^® bag).  The amount of water that can permeate from the container into the overwrap is insufficient to affect the solution significantly.  Solutions in contact with the flexible container can leach out certain of the container’s chemical components in very small amounts within the expiration period.  The suitability of the container material has been confirmed by tests in animals according to USP biological tests for plastic containers.  Exposure to temperatures above 25ºC/77ºF during transport and storage will lead to minor losses in moisture content.  Higher temperatures lead to greater losses.  It is unlikely that these minor losses will lead to clinically significant changes within the expiration period.

Magnesium (Mg ⁺⁺) is an important cofactor for enzymatic reactions and plays an important role in neurochemical transmission and muscular excitability.

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, but it does not adversely affect the mother, fetus or neonate when used as directed in eclampsia or pre-eclampsia.  Normal serum magnesium levels range from 1.3 to 2.1 mEq/liter.

As serum magnesium rises above 4 mEq/liter, the deep tendon reflexes are first decreased and then disappear as the serum level approaches 10 mEq/liter.  At this level respiratory paralysis may occur.  Heart block also may occur at this or lower serum levels of magnesium.  

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.

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 sulfate in water for injection is indicated for the prevention and control of seizures in pre-eclampsia and eclampsia, respectively.  When used judiciously it effectively prevents and controls the convulsions of eclampsia without producing deleterious depression of the central nervous system of the mother or infant.  However, other effective drugs are available for this purpose.

Intravenous magnesium should not be given to mothers with toxemia of pregnancy during the two hours preceding delivery.

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.

Parenteral use in the presence of renal insufficiency may lead to magnesium intoxication.

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 every four hours.  Monitoring serum magnesium levels and the patient’s clinical status is essential to avoid the consequences of overdosage in toxemia.  Clinical indications of a safe dosage regimen include the presence of the patellar reflex (knee jerk) and absence of respiratory depression (approximately 16 breaths or more/minute).  Serum magnesium levels usually sufficient to control convulsions range from 3 to 6 mg/100 mL (2.5 to 5 mEq/liter).  The strength of the deep tendon reflexes begins to diminish when serum magnesium levels exceed 4 mEq/liter.  Reflexes may be absent at 10 mEq magnesium/liter, where respiratory paralysis is a potential hazard.  An injectable calcium salt should be immediately available to counteract the potential hazards of magnesium intoxication in eclampsia.

Magnesium sulfate in water for injection should be administered slowly to avoid producing hypermagnesemia.

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.

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.  In the event of overdosage, artificial ventilation must be provided until a calcium salt can be injected IV to antagonize the effects of magnesium.

Magnesium sulfate in water for injection is intended for intravenous use only.  For the management of pre-eclampsia or eclampsia, intravenous infusions of dilute solutions of magnesium (1% to 8%) are often given in combination with intramuscular injections of 50% magnesium sulfate injection, USP.  Therefore, in the clinical conditions cited below, both forms of therapy are noted, as appropriate.  

Continuous maternal administration of magnesium sulfate in pregnancy beyond 5 to 7 days can cause fetal abnormalities.

Magnesium Sulfate in Water for Injection is supplied in single-dose flexible containers as follows:

*Partial fill container 50 mL volume in 100 mL container.

**As the heptahydrate.

WARNING: DO NOT USE FLEXIBLE CONTAINER IN SERIES CONNECTIONS.

This container is not made with natural rubber latex or polyvinyl chloride (PVC), Non-DEHP.

Store at 20° to 25°C (68° to 77°F) [see USP Controlled Room Temperature].  Protect from freezing.

1. Yokoyama K, Takahashi N, Yada Y. Prolonged maternal magnesium administration and bone metabolism in neonates. Early Human Dev. 2010; 86(3):187-91. Epub 2010 Mar 12.
2. Wedig KE, Kogan J, Schorry EK et al. Skeletal demineralization and fractures caused by fetal magnesium toxicity. J Perinatol. 2006; 26(6):371-4.
3. Nassar AH, Sakhel K, Maarouf H, et al. Adverse maternal and neonatal outcome of prolonged course of magnesium sulfate tocolysis. Acta Obstet Gynecol Scan. 2006; 85(9):1099-103.
4. Malaeb SN, Rassi A, Haddad MC. Bone mineralization in newborns whose mothers received magnesium sulphate for tocolysis of premature labor. Pediatr Radiol. 2004; 34(5):384-6. Epub 2004 Feb 18.
5. Matsuda Y, Maeda Y, Ito M, et al. Effect of magnesium sulfate treatment on neonatal bone abnormalities. Gynecol Obstet Invest. 1997; 44(2):82-8.
6. Schanler RJ, Smith LG, Burns PA. Effects of long-term maternal intravenous magnesium sulfate therapy on neonatal calcium metabolism and bone mineral content. Gynecol Obstet Invest. 1997; 43(4):236-41.
7. Santi MD, Henry GW, Douglas GL. Magnesium sulfate treatment of preterm labor as a cause of abnormal neonatal bone mineralization. J Pediatr Orthop. 1994; 14(2):249-53.
8. Holocomb WL, Shackelford GD, Petrie RH. Magnesium tocolysis and neonatal bone abnormalities: a controlled study. Obstet Gynecol. 1991; 78(4):611-4.
9. Cumming WA, Thomas VJ. Hypermagnesemia: a cause of abnormal metaphyses in the neonate. Am J Roentgenol. 1989; 152(5):1071-2.
10. Lamm CL, Norton KL, Murphy RJ. Congenital rickets associated with magnesium sulfate infusion for tocolysis. J Pediatr. 1988; 113(6):1078-82.
11. McGuinness GA, Weinstein MM, Cruikshank DP, et al. Effects of magnesium sulfate treatment on perinatal calcium metabolism. II. Neonatal responses. Obstet Gynecol. 1980; 56(5):595-600.
12. Riaz M, Porat R, Brodsky NL, et al. The effect of maternal magnesium sulfate treatment on newborns: a prospective controlled study. J Perinatol. 1998; 18(6 pt 1):449-54.

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Manufactured for:

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Made in Norway

451339A

Revised: October 2014

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