An injectable mineral given IV or IM to prevent and stop seizures in preeclampsia and eclampsia, and to replace magnesium when levels are low. Too much causes loss of reflexes, slowed breathing, and heart problems, so reflexes, breathing, urine output, and levels are checked, and IV calcium reverses toxicity.
Labeled use. Prevention of seizures in preeclampsia and control of seizures in eclampsia.
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Labeled use. Replacement therapy, especially acute hypomagnesemia with tetany, and prevention during TPN.
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The drug of choice to prevent and treat eclamptic seizures, superior to phenytoin and diazepam for this use. It does not treat the hypertension of preeclampsia, which needs labetalol, hydralazine, or nifedipine. It is also used for torsades de pointes and fetal neuroprotection before early preterm delivery, which are outside this label.
Magnesium is a cofactor for many enzymes and governs neurochemical transmission and muscle excitability. It prevents and controls seizures by blocking neuromuscular transmission and reducing acetylcholine release at the motor end-plate. It causes peripheral vasodilation. Above 4 mEq/L deep tendon reflexes fall, and near 10 mEq/L they disappear and respiratory paralysis can occur. IV onset is immediate and lasts about 30 minutes; IM onset is about 1 hour, lasting 3 to 4 hours. It is excreted only by the kidneys.
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The label does not state a narrow therapeutic index or direct dosing by measured blood levels against a target range. Levels and reflexes are monitored for toxicity.
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Doses come from the FDA label. Study tool, not for clinical decisions.
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Use with caution; the kidneys are its only route of elimination and renal insufficiency can cause magnesium intoxication. In severe renal insufficiency, the maximum is 20 g in 48 hours with frequent magnesium levels.
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An injectable calcium salt counteracts magnesium toxicity: IV calcium, 10 to 20 mL of a 5% solution. Keep it immediately available during treatment for eclampsia. Provide artificial ventilation until calcium takes effect; subcutaneous physostigmine 0.5 to 1 mg may help. Newborns with hypermagnesemia may need resuscitation, ventilation, and IV calcium.
Use only if clearly needed. Continuous use beyond 5 to 7 days can cause fetal hypocalcemia, skeletal demineralization, osteopenia, and neonatal fractures. Infusions, especially for more than 24 hours before delivery, can cause neonatal magnesium toxicity. Use for preterm labor is unapproved. Used as directed in preeclampsia and eclampsia, it does not harm the mother, fetus, or newborn.
Magnesium passes into milk during parenteral treatment; use with caution while nursing.
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Dilute to 20% or less before IM injection in infants and children. In TPN, infants usually need 0.25 to 1.25 g (2 to 10 mEq) a day. Premature neonates are at particular risk of aluminum toxicity from prolonged parenteral use.
Older adults often need lower doses because of reduced renal function. In severe impairment, do not exceed 20 g in 48 hours, and monitor serum magnesium.
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