magnesium (Antidote) (Rx)

Frequency Not Defined

Flushing

Hypotension

Hypothermia

CNS depression

Motor & respiratory paralysis

Abnormal ECG

Diarrhea

Heart block

Prolonged bleeding time

Contraindications

Hypersensitivity

Heart block or myocardial damage

Diabetic coma

Myasthenia gravis

Cautions

Serum levels poorly correlate to body stores

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

Do not use in 5% dextrose Injection with unapproved tocolytics (eg, beta-adrenergic agents such as terbutaline, or with calcium channel blockers such as nifedipine); serious adverse events including pulmonary edema and hypotension have occurred

Aluminum toxicity

• Magnesium sulfate in 5% dextrose injection contains aluminum that may be toxic (magnesium sulfate in 5% dextrose injection contains <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 >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

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 suspected, discontinue use of magnesium sulfate in 5% dextrose injection immediately; secure patient's airway; consider intensive care unit admission and elective intubation, if respiratory failure is anticipated; once 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

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 presence of 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 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; urine output should be maintained at level of 100 mL per 4 hours
• Monitoring serum magnesium levels and patient's clinical status is essential to avoid consequences of overdosage in patients with preeclampsia; discontinuation of magnesium infusion is recommended when urine output is <100 mL every 4 hours to avoid magnesium toxicity, especially if serum creatinine is increasing progressively

Pregnancy

Continuous administration of magnesium sulfate beyond 5-7 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 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 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 5-7 days not recommended

Magnesium Sulfate in 5% dextrose injection is indicated in pregnant women for prevention of eclampsia in women with preeclampsia and treatment of seizures and prevention of recurrent seizures in women with eclampsia

Magnesium sulfate in 5% dextrose injection is not approved for treatment of pre-term labor

Administration of magnesium sulfate in 5% dextrose injection to pregnant women longer than 5-7 days may lead to hypocalcemia and bone abnormalities in developing fetus, including skeletal demineralization and osteopenia

Lactation

Use of intravenous magnesium in pregnant women increases human milk magnesium concentrations only slightly and oral absorption of magnesium by infant is poor; the effect of intravenous magnesium on milk production is unknown

The developmental and health benefits to neonate of breastfeeding should be considered along with mother's clinical need for magnesium sulfate in 5% dextrose injection and any potential adverse effects on breastfed infant from magnesium sulfate in 5% dextrose injection or from underlying maternal condition

Pregnancy Categories

A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.

B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.

C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.

D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.

X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.

NA: Information not available.

Mechanism of Action

Co-factor in enzymatic processes

Slows the rate of S-A node impulse formation in the myocardium and prolongs conduction time

Stabilizes excitable membranes by promoting the movement of sodium, calcium, and potassium in and out of the cell

Pharmacokinetics

Distribution: Bone (50-60%); extracellular fluid (1-2%)

Protain binding: 30%

Excretion: Urine