MAGNESIUM SULFATE IN PLASTIC CONTAINER
Clinical safety rating: caution
Comprehensive clinical and safety monograph for MAGNESIUM SULFATE IN PLASTIC CONTAINER (MAGNESIUM SULFATE IN PLASTIC CONTAINER).
Magnesium sulfate causes decreased release of acetylcholine at the neuromuscular junction, reducing muscle contractility. It also blocks calcium channels, leading to vasodilation and anticonvulsant effects.
| Metabolism | Magnesium sulfate is primarily excreted unchanged by the kidneys. It does not undergo significant hepatic metabolism. |
| Excretion | Primarily renal (glomerular filtration); >90% excreted unchanged in urine. Biliary/fecal elimination is negligible (<1%). |
| Half-life | Normal renal function: 4–6 hours (terminal). In oliguria or anuria, half-life may extend to >24 hours, requiring dose adjustment. |
| Protein binding | Approximately 30–40% bound to albumin. |
| Volume of Distribution | 0.2–0.3 L/kg. Distributes mainly in extracellular fluid; crosses placenta and blood-brain barrier. |
| Bioavailability | IV: 100%. IM: ~80% (variable). Oral: <20% (poor, due to limited absorption; primarily used for catharsis). |
| Onset of Action | IV: Immediate (1–2 minutes). IM: 30–60 minutes. Oral: Not relevant for systemic effects (2–4 hours for catharsis). |
| Duration of Action | IV: 30 minutes (anticonvulsant). IM: 3–4 hours. Continuous IV infusion maintains effect. Oral: 3–6 hours (cathartic). |
IV: 1-4 g as a 10-20% solution, rate not exceeding 1 g/min; for eclampsia: 4-5 g IV bolus then 1-2 g/hour IV infusion.
| Dosage form | INJECTABLE |
| Renal impairment | GFR <20 mL/min: maximum dose 2 g; avoid use if anuria. GFR 20-50 mL/min: reduce dose by 25-50%. |
| Liver impairment | Child-Pugh Class B or C: reduce dose by 50% and monitor serum magnesium levels. |
| Pediatric use | IV: 20-40 mg/kg/dose (max 2 g) as 10% solution; for severe hypomagnesemia: 25-50 mg/kg/dose q4-6h. |
| Geriatric use | Reduce initial dose by 25-50%; infuse over longer period; monitor renal function and serum magnesium closely. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for MAGNESIUM SULFATE IN PLASTIC CONTAINER (MAGNESIUM SULFATE IN PLASTIC CONTAINER).
| Breastfeeding | Magnesium is excreted into breast milk; estimated infant dose approximately 1-2% of maternal weight-adjusted dose. M/P ratio not established. Risk of infant diarrhea and hypotonia with high maternal doses. Avoid prolonged high-dose therapy during breastfeeding. |
| Teratogenic Risk | Prolonged use (≥5-7 days) in pregnancy is associated with fetal hypocalcemia, skeletal demineralization, and neonatal hypermagnesemia. No increased risk of major malformations with standard short-term use. Third trimester: risk of neonatal hypotonia, respiratory depression if given near delivery. Continuous infusion for tocolysis >48 hours increases risk of neonatal bone abnormalities. |
■ FDA Black Box Warning
Continuous infusion of magnesium sulfate can cause hypermagnesemia, which may lead to respiratory depression or cardiac arrest. Only use with continuous monitoring of serum magnesium levels and clinical status.
| Serious Effects |
Hypersensitivity to magnesium sulfate; heart block or myocardial damage; severe renal impairment (anuria or oliguria); hypermagnesemia.
| Precautions | Risk of hypermagnesemia, especially in renal impairment; monitor serum magnesium levels, deep tendon reflexes, and respiratory rate; use with caution in patients with myasthenia gravis or heart block; avoid extravasation due to risk of tissue necrosis. |
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| Fetal Monitoring | Monitor maternal deep tendon reflexes, respiratory rate (≥16/min), urine output (≥100 mL/4h), serum magnesium levels (therapeutic range 4-7 mEq/L). Fetal: continuous fetal heart rate monitoring during parenteral administration. Neonatal: assess for hypotonia, respiratory effort, and serum magnesium if indicated. |
| Fertility Effects | No known adverse effects on fertility. Magnesium is an essential cation; deficiency may impair ovulation. No evidence of reproductive toxicity at therapeutic doses. |