magnesium sulfate (parenteral)
High Alert Medication: This medication bears a heightened risk of causing significant patient harm when it is used in error.
mineral and electrolyte replacements/supplements
- Treatment/prevention of hypomagnesemia.
- Prevention and treatment of seizures associated with severe eclampsia or pre-eclampsia.
- Treatment of torsades de pointes.
- Adjunctive treatment for bronchodilation in moderate to severe acute asthma.
- Essential for the activity of many enzymes.
- Plays an important role in neurotransmission and muscular excitability.
- Replacement in deficiency states.
- Resolution of eclampsia.
Absorption: IV administration results in complete bioavailability; well absorbed from IM sites.
Distribution: Widely distributed. Crosses the placenta and is present in breast milk.
Metabolism and Excretion: Excreted primarily by the kidneys.
TIME/ACTION PROFILE (anticonvulsant effect)
|IM||60 min||unknown||3–4 hr|
- Heart block.
Use Cautiously in:
- Renal impairment;
- OB: Avoid using for more than 5–7 days for preterm labor (may ↑ risk of hypocalcemia and bone changes in newborn); avoid continuous use during active labor or within 2 hr of delivery due to potential for magnesium toxicity in newborn
- Geri: Older adults may require ↓ dosage due to age-related ↓ in renal function.
Adverse Reactions/Side Effects
CV: arrhythmias, bradycardia, hypotension
Derm: flushing, sweating
MS: muscle weakness
Resp: ↓ respiratory rate
* CAPITALS indicate life-threatening.
Underline indicate most frequent.
May potentiate calcium channel blockers and neuromuscular blocking agents.
Treatment of Deficiency
IM IV (Adults): Severe deficiency– 8–12 g/day in divided doses; mild deficiency– 1 g every 6 hr for 4 doses or 250 mg/kg over 4 hr.
IM IV (Children >1 mo): 25–50 mg/kg/dose every 4–6 hr for 3–4 doses, maximum single dose: 2 g.
IV Neonates: 25–50 mg/kg/dose every 8–12 hr for 2–3 doses.
Seizures Associated with Eclampsia/Pre-Eclampsia
IV (Adults): 4–6 g loading dose over 15–30 min at onset of labor or induction/cesarean delivery, followed by 1–2 g/hr continuous infusion for ≥24 hours after delivery (max infusion rate = 3 g/hr). If seizure occurs while receiving magnesium, an additional bolus of 2–4 g may be administered over ≥5 minutes. Max dose = 40 g/24 hr.
IM (Adults): 10 g loading dose administered as 5 g in each buttock at onset of labor or induction/cesarean delivery, followed by 5 g every 4 hours for ≥24 hours after delivery.
Torsades de Pointes
IV (Infants and Children): 25–50 mg/kg/dose, maximum dose: 2 g.
IV (Adults): 2 g single dose.
IV Children: 25 mg/kg/dose, maximum dose: 2 g.
IV (Adults): 4–24 mEq/day.
IV Children: 0.25–0.5 mEq/kg/day.
Availability (generic available)
Solution for injection (8.1 mEq Mg/g): 500 mg/mL (50%)
Premixed infusion: 1 g/100 mL, 2 g/50 mL, 4 g/50 mL, 4 g/100 mL, 20 g/500 mL, 40 g/1000 mL
- Hypomagnesemia/Anticonvulsant: Monitor pulse, BP, respirations, and ECG frequently during administration of parenteral magnesium sulfate. Respirations should be at least 16/min before each dose.
- Monitor neurologic status before and throughout therapy. Institute seizure precautions. Patellar reflex (knee jerk) should be tested before each parenteral dose of magnesium sulfate. If response is absent, no additional doses should be administered until positive response is obtained.
- Monitor newborn for hypotension, hyporeflexia, and respiratory depression if mother has received magnesium sulfate.
- Monitor intake and output ratios. Urine output should be maintained at a level of at least 100 mL/4 hr.
Lab Test Considerations:
Monitor serum magnesium levels and renal function periodically during administration of parenteral magnesium sulfate.
- High Alert: Accidental overdose of IV magnesium has resulted in serious patient harm and death. Have second practitioner independently double-check original order, dose calculations, and infusion pump settings. Do not confuse milligram (mg), gram (g), or milliequivalent (mEq) doses.
- IM IM route should only be used when unable to establish venous access. Administer deep IM into gluteal sites. Administer subsequent injections in alternate sides. Dilute to a concentration of 200 mg/mL prior to injection.
- IV Push: Diluent: 50% solution must be diluted in 0.9% NaCl or D5W to a concentration of ≤20% prior to administration. Concentration: ≤20%.
- Rate: Administer over several min at a rate not to exceed 150 mg/min. In patients not in cardiac arrest, rapid administration may cause hypotension and asystole.
- Intermittent Infusion: Diluent: 50% solution must be diluted in 0.9% NaCl or D5W to a concentration of ≤20% prior to administration. Concentration: ≤20%.
- Rate: For ventricular tachycardia/torsades: Infuse over 10–20 min; rapid infusion may cause hypotension. For severe asthma exacerbation: Infuse over 15–60 min.
- Continuous Infusion: Diluent: Dilute in D5W, 0.9% NaCl, or LR. Concentration: 0.5 mEq/mL (60 mg/mL) (may use maximum concentration of 1.6 mEq/mL) (200 mg/mL) in fluid-restricted patients.
- Rate: Infuse over 2–4 hr. Do not exceed a rate of 1 mEq/kg/hr (125 mg/kg/hr). When rapid infusions are needed (severe asthma or torsade de pointes) may infuse over 10–20 min.
- Y-Site Compatibility:
- aminocaproic acid
- arsenic trioxide
- ascorbic acid
- calcium gluconate
- daunorubicin hydrochloride
- doxorubicin liposome
- epoetin alfa
- etoposide phosphate
- folic acid
- gemtuzumab ozogamicin
- insulin, regular
- lactated Ringer's
- leucovorin calcium
- penicillin G
- potassium acetate
- potassium chloride
- sodium acetate
- sodium bicarbonate
- vitamin B complex with C
- zoledronic acid
- Y-Site Incompatibility:
- amphotericin B deoxycholate
- amphotericin B lipid complex
- amphotericin B liposome
- calcium chloride
- dexamethasone sodium phosphate
- doxorubicin hydrochloride
- methylprednisolone sodium succinate
- Explain purpose of medication to patient and family.
- Rep: Monitor vital signs, oxygen saturation, respiration, deep tendon reflexes, level of consciousness, fetal heart rate, maternal uterine activity, and renal function when used during pregnancy. Monitor magnesium concentrations every 4 hr in patients with renal dysfunction (every 2 hr if serum magnesium is elevated). Breast milk concentrations are increased for only ~24 hr after end of therapy. When used for prevention of seizures, magnesium sulfate is considered compatible with breastfeeding.
- Normal serum magnesium concentrations.
- Control of seizures associated with toxemias of pregnancy.
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