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.
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High-alert medication. Magnesium sulfate injection is on the ISMP acute care high-alert list.
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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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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.
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.
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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