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MAGNESIUM SULFATE (magnesium sulfate injection, USP) Warnings and Precautions


5.1 Fetal-Neonatal Toxicity with Prolonged Use

Continuous administration of magnesium sulfate beyond 5 to 7 days in pregnant women can lead to hypocalcemia and bone abnormalities in the developing fetus, including skeletal demineralization and osteopenia. In addition, cases of neonatal fracture have been reported.

Neonates of women receiving Magnesium Sulfate in 5% Dextrose Injection (especially with prolonged maternal use) are at risk for magnesium toxicity including hyporeflexia, hypotonia, and respiratory depression. There is one reported case of neonatal death as the result of magnesium toxicity after transplacental exposure.

The shortest duration of magnesium sulfate treatment that can lead to fetal harm is not known. Administration of Magnesium Sulfate in 5% Dextrose Injection beyond 5 to 7 days is not recommended.

5.2 Risk of Magnesium Toxicity

Patients receiving Magnesium Sulfate in 5% Dextrose Injection are at risk for magnesium toxicity including respiratory depression, acute renal failure and rarely, pulmonary edema.

Monitor clinical signs of magnesium toxicity (for example, facial edema, diminished strength of deep tendon reflexes, respiratory depression) and magnesium concentrations during infusions of Magnesium Sulfate in 5% Dextrose Injection. 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 per minute). Serum magnesium concentrations usually sufficient to control convulsions range from 3 to 6 mg per 100 mL (2.5 to 5 mEq per liter). The strength of the deep tendon reflexes begins to diminish when serum magnesium concentrations exceed 4 mEq per liter. Reflexes may be absent at concentration of 10 mEq per liter, at which point respiratory paralysis is a potential hazard. An injectable calcium salt should be immediately available to counteract the potential hazards of magnesium toxicity in patients with preeclampsia and eclampsia. If there is significant magnesium toxicity, stop the Magnesium Sulfate in 5% Dextrose Injection infusion and recheck serum magnesium concentration.

Patients with renal impairment are at greater risk of magnesium toxicity because magnesium is excreted by the body solely by the kidneys [see Use in Specific Populations (8.6)]. Urine output should be maintained at a level of 100 mL per 4 hours. Monitoring serum magnesium levels and the patient's clinical status is essential to avoid the consequences of overdosage in patients with preeclampsia. Discontinuation of the magnesium infusion is recommended when urine output is less than 100 mL every 4 hours to avoid magnesium toxicity, especially if serum creatinine is increasing progressively.

5.3 Risk of Elevated Blood Glucose

Solutions containing dextrose should be used with caution in patients with known prediabetes or diabetes mellitus given the risk of elevated blood glucose.

5.4 Co-administration with Unapproved Tocolytics

Do not use Magnesium Sulfate in 5% Dextrose Injection with unapproved tocolytics (e.g., beta adrenergic agents such as terbutaline, or with calcium channel blockers such as nifedipine). Serious adverse events including pulmonary edema and hypotension have occurred [see Drug Interactions (7)].

5.5 Aluminum Toxicity

Magnesium Sulfate in 5% Dextrose Injection contains aluminum that may be toxic (Magnesium Sulfate in 5% Dextrose Injection contains less than 25 mcg/L of aluminum). Aluminum may reach toxic concentrations with prolonged parenteral administration in patients with renal impairment.

Patients with renal impairment who receive parenteral concentrations of aluminum at greater than 4 to 5 mcg/kg/day, accumulate aluminum at concentrations associated with central nervous system and bone toxicity. Tissue loading may occur at even lower rates of administration.

5.6 Exacerbation of Myasthenia Gravis

Magnesium Sulfate in 5% Dextrose Injection is contraindicated in patients with known myasthenia gravis.

Use of magnesium sulfate in patients with underlying myasthenia gravis can precipitate a myasthenic crisis. Myasthenic crisis is a life-threatening condition characterized by neuromuscular respiratory failure. Symptoms of myasthenic crisis may include difficulty swallowing, ptosis, facial droop, weakness and/or difficulty breathing that may require intubation.

If myasthenic crisis is suspected, discontinue use of Magnesium Sulfate in 5% Dextrose Injection immediately. Secure the patient's airway. Consider intensive care unit admission and elective intubation, if respiratory failure is anticipated. Once the airway is secure, confirm the diagnosis. Therapies include plasmapheresis and plasma exchange or intravenous immunoglobulin (IVIG) and immunomodulating therapy in addition to high-dose glucocorticoids.

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