Individualize dose based on patient requirement and response. Discontinue as soon as desired response is obtained. Doses are expressed as magnesium sulfate unless stated otherwise. 1 Gm of magnesium sulfate = 98.6 mg elemental magnesium = 8.12 mEq of elemental magnesium.
Pre-eclampsia and eclampsia:
Several regimens in literature. The recommended loading dose is 4 to 6 Gm over 15 minutes followed by a recommended maintenance dose of 1 to 2 Gm/hr. For patients with eclampsia, therapy should continue until seizures cease. Consider giving an additional 2-Gm dose for patients with recurrent eclampsia.
Another regimen suggests a total initial dose of 10 to 14 Gm. This may be achieved by administering 4 to 5 Gm in 250 mL of D5W or NS IV. Simultaneously, IM doses of up to 10 Gm (5 Gm or 10 mL of the undiluted 50% solution in each buttock) are given. Alternatively, the initial IV dose of 4 Gm may be given by diluting the 50% solution to a 10% or 20% concentration that is injected over 3 to 4 minutes. Subsequent 4- to 5-Gm doses may be given IM every 4 hours as needed, or a continuous infusion of 1 to 2 Gm/hr may be initiated.
Do not exceed 30 to 40 Gm/24 hr. Frequent monitoring required; see Dose Adjustments, Precautions, and Monitor.
Seizures associated with epilepsy, glomerulonephritis, or hypothyroidism:
1 Gm IV.
Hypomagnesemia (mild):
1 Gm IM every 6 hours for 4 doses. Another source recommends 1 to 4 Gm administered IV at a rate of 1 Gm/hr or less.
5 Gm (40 mEq) in 1,000 mL D5W or NS as an infusion evenly distributed over 3 hours. Another source recommends 4 to 8 Gm IV administered at a rate of 1 Gm/hr or less for asymptomatic patients. If symptomatic, may administer a dose of 4 Gm or less over 4 to 5 minutes.
Parenteral nutrition in adults:
8 to 24 mEq/24 hr IV (1 to 3 Gm).
Paroxysmal atrial tachycardia (unlabeled):
3 to 4 Gm IV (30 to 40 mL of a 10% solution) over 30 seconds with extreme caution. Reserve for patients in whom simpler measures have failed and in whom there is no evidence of myocardial damage.
Reduction of cerebral edema (unlabeled):
2.5 Gm IV (25 mL of a 10% solution).
Cardiac arrest (hypomagnesemia or torsades de pointes):
AHA recommends 1 to 2 Gm (2 to 4 mL of a 50% solution) diluted in 10 mL D5W as a bolus.
AHA recommends a loading dose of 1 to 2 Gm in 50 to 100 mL D5W as an infusion over 5 to 60 minutes. May follow with an infusion of 0.5 to 1 Gm/hr and titrate to control the torsades.
1 to 2 Gm IV.
Alleviate bronchospasm in acute asthma (unlabeled):
2 Gm given IV over 20 minutes. Usually given concurrently with inhaled albuterol (Proventil) and IV corticosteroids.
All pediatric doses are unlabeled; see Maternal/Child.
25 to 50 mg/kg of body weight/dose. May repeat at 6-hour intervals for 2 to 3 doses, then recheck serum magnesium. Maximum recommended single dose is 2 Gm.
Pulseless VT with torsades de pointes:
AHA recommends 25 to 50 mg/kg/dose IV push. A 50% solution equals 500 mg/mL. Maximum recommended dose is 2 Gm.
25 to 75 mg/kg as an infusion over 20 minutes. Maximum recommended dose is 2 Gm.
0.3 to 0.5 mEq/kg/day (dose expressed as elemental magnesium).
Reduce dose of other CNS depressants (e.g., narcotics, barbiturates) when given in conjunction with magnesium sulfate.
■ Reduce dose in impaired renal function and in the elderly.
■ In patients with severe renal impairment and/or a urine output less than 0.5 mL/kg/hr, initiate prevention or treatment of eclampsia with a loading dose of 4 Gm in D5W followed by a maintenance infusion of 1 Gm/hr. Titrate to maintain the concentration in the target range and monitor closely for S/S of magnesium toxicity. A lower maintenance dose requirement is likely in these patients. Do not exceed the maximum recommended dose of 20 Gm of magnesium sulfate over 48 hours.
■ Reduce dose by 50% in patients with renal dysfunction being treated for hypomagnesemia; close monitoring is required.
Concentrated solutions must be diluted to a concentration of 20% (200 mg/mL) or less for IV administration. D5W and NS are the most common diluents. Available in various containers in multiple concentrations and also in multiple concentrations as a premixed solution in sterile water for injection or in 5% dextrose. See Usual Dose for specific dilutions. May be given through Y-tube of infusion set.
Store at CRT. Protect from freezing. Contains no preservative. Discard any unused solution.
Will form various precipitates with alcohol (in high concentrations), alkali carbonates and bicarbonates, alkali hydroxides, arsenates, barium, calcium, clindamycin, heavy metals, hydrocortisone sodium succinate, phosphates, salicylates, strontium, and tartrates. Use caution; consult pharmacist.
Other sources suggest specific compatibilities dependent on concentration and manufacturer; consult a pharmacist.
150 mg (1.5 mL of a 10% solution or its equivalent) over at least 1 minute, must be diluted first, or as directed in Usual Dose.
As directed in Usual Dose.
An important cofactor for enzymatic reactions and plays an important role in neurochemical transmission and muscular excitability. It prevents or controls seizures by blocking neuromuscular transmission and decreasing the amount of acetylcholine release. Acts peripherally to produce vasodilation and may cause a lowering of BP at higher doses. Has a depressant effect on the CNS but does not adversely affect the woman, fetus, or neonate when used as directed in eclampsia or pre-eclampsia. Onset of anticonvulsant action is immediate and lasts for about 30 minutes. Average half-life in females with pre-eclampsia is approximately 4 to 5 hours. Excreted in the urine. Secreted in breast milk. Crosses the placental barrier.
Replacement therapy in magnesium deficiency (e.g., acute hypomagnesemia accompanied by signs of tetany similar to those seen in hypocalcemia).
■ Correction or prevention of hypomagnesemia in patients receiving TPN.
■ Prevention and control of seizures in pre-eclampsia and eclampsia, respectively.
Control of seizures associated with epilepsy, glomerulonephritis, hypothyroidism.
■ Reduction of cerebral edema.
■ Acute nephritis in pediatric patients to control hypertension, encephalopathy, and convulsions.
■ Treatment of torsades de pointes, ventricular tachycardia, and ventricular fibrillation (VT/VF) caused by hypomagnesemia.
■ Counteract muscle-stimulating effects of barium poisoning.
■ Treatment of paroxysmal atrial tachycardia.
■ Treatment of acute asthma in patients who do not respond to conventional therapy.
Continuous administration of magnesium sulfate beyond 5 to 7 days to pregnant females can lead to hypocalcemia and bone abnormalities in the developing fetus, including skeletal demineralization, osteopenia, and neonatal fracture.
■ Patients receiving magnesium sulfate are at risk for magnesium toxicity, including respiratory depression, acute renal failure and, rarely, pulmonary edema.
■ Use caution in impaired renal function; may result in magnesium toxicity.
■ Some solutions may contain aluminum. In impaired kidney function, aluminum may reach toxic levels. Premature neonates are particularly at risk because of their immature kidneys and requirement for calcium and phosphate, which also contain aluminum. Research indicates that patients with impaired renal function who receive greater than 4 to 5 mcg/kg/day of parenteral aluminum are at risk for developing CNS or bone toxicity associated with aluminum accumulation. Tissue loading may occur at even lower rates of administration.
■ Administer with caution if flushing and sweating occur (first signs of vasodilation).
■ Solutions containing dextrose should be used with caution in patients with known prediabetes or diabetes mellitus given the risk of elevated blood glucose.
■ Use of magnesium sulfate in patients with underlying myasthenia gravis can precipitate a myasthenic crisis; see Contraindications.
■ See Drug/Lab Interactions.
Discontinue IV administration when the desired therapeutic effect is obtained.
■ Monitor for clinical signs of magnesium toxicity (e.g., facial edema, diminished strength of deep tendon reflexes, respiratory depression).
■ Monitor magnesium levels. Normal plasma magnesium levels range from 1.5 to 2.5 mEq/L. Consider targeting maintenance dose to achieve serum magnesium concentrations of 2.5 to 5 mEq/L (3 to 6 mg/100 mL) in patients with eclampsia. Deep tendon reflexes decrease at plasma magnesium levels above 4 mEq/L and disappear as levels approach 10 mEq/L. Respiratory paralysis will occur at this level.
■ With each repeated dose, test patellar reflex (knee jerks) and observe respirations. If the knee jerk is absent or if respirations are less than 16/min, do not give additional magnesium sulfate.
■ Equipment to maintain artificial ventilation must be available at all times. Patient must be continuously observed.
■ Maintain minimum of 100 mL of urine or more during the 4 hours preceding each dose.
If magnesium is given for the treatment of preterm labor, inform the woman that the efficacy and safety of such use have not been established and that use beyond 5 to 7 days may cause fetal abnormalities.
■ Promptly report symptoms of magnesium toxicity (e.g., difficulty breathing, flushing, sweating, weakness).
Continuous administration beyond 5 to 7 days to pregnant females can lead to hypocalcemia and bone abnormalities in the developing fetus; see Precautions. Use during pregnancy only if clearly needed.
■ Administration of magnesium is not approved for treatment for preterm labor. Safety and efficacy have not been established. Administration of magnesium outside its approved indication in pregnant females should be by trained obstetric personnel in a hospital setting with appropriate obstetric care facilities.
■ A continuous infusion given to control convulsions in toxemic mothers before delivery (especially in the 24 hours preceding) may cause signs of magnesium toxicity in the newborn (e.g., neuromuscular or respiratory depression).
■ Use caution during breast-feeding.
■ Safety for use in pediatric patients not established. Safety and effectiveness have been established for the prevention of eclampsia in adolescents with pre-eclampsia and the treatment of seizures and prevention of recurrent seizures in adolescents with eclampsia.
See Dose Adjustments.
Additive CNS depressant effects when used concomitantly with barbiturates, hypnotics, narcotics, or systemic anesthetics. See Dose Adjustments and Monitor.
■ Potentiation and prolongation of neuromuscular blockade is possible when used with neuromuscular blocking agents (e.g., vecuronium, succinylcholine). Monitor patient closely. Dose adjustment of the neuromuscular blocking agent and reversal agent may be necessary.
■ An exaggerated hypotensive response is possible with concomitant use of magnesium and dihydropyridine calcium channel blockers (e.g., amlodipine, nicardipine, nifedipine); monitor vital signs frequently.
■ If calcium is used to treat magnesium toxicity, use in digitalized patients may cause serious changes in cardiac conduction, resulting in heart block. Use with extreme caution.
■ Drugs that may induce magnesium loss (e.g., alcohol, aminoglycosides, amphotericin B, cisplatin, cyclosporine, digitalis, diuretics) may reduce magnesium concentrations, affecting efficacy; monitor magnesium concentrations closely and adjust dose as needed.
■ Avoid use with unapproved tocolytics (e.g., beta-adrenergic agents such as terbutaline or calcium channel blockers such as nifedipine); serious adverse events, including pulmonary edema and hypotension, have occurred.
Usually the result of magnesium intoxication. Cardiac and CNS depression proceeding to respiratory paralysis, circulatory collapse, depressed or absent knee jerk reflex, flaccid paralysis, flushing, hypocalcemia with signs of tetany, hypotension, hypothermia, and sweating are most common. Other reported side effects include bradycardia, decreased respiratory rate, hypermagnesemia, lethargy, myasthenic crisis, pulmonary edema, sedation, somnolence, and visual disturbances.
Discontinue the drug and notify the physician of the occurrence of any side effect. An intravenous calcium salt (10 to 20 mL of a 5% solution [diluted if desirable with NS]) may be used to counteract the effects of hypermagnesemia. Physostigmine 0.5 to 1 mg SQ may be helpful. Treat hypotension with dopamine. Employ artificial ventilation as necessary and resuscitate as necessary. Hemodialysis is effective in overdose. Hypermagnesemia in the newborn may require resuscitation, endotracheal intubation, assisted ventilation, and IV calcium.