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# Magnesium Sulphate
## Overview
Magnesium sulfate is an electrolyte that plays a crucial role in numerous biochemical functions. It is an essential mineral for normal muscle and nerve function, blood glucose control, and blood pressure regulation.
## Primary Indications
* Treatment of magnesium deficiency (hypomagnesemia).
* Management of eclampsia and pre-eclampsia.
* Treatment of torsades de pointes.
* Management of severe asthma exacerbations (off-label, adjunctive therapy).
* Prevention and treatment of hypomagnesemia in patients receiving certain medications (e.g., amphotericin B, cisplatin, diuretics).
## Adult Dosing
Dosing is highly variable based on indication and patient status.
* **Hypomagnesemia:**
* **Severe (serum Mg < 1.3 mg/dL or symptomatic):** Intravenous administration is typically preferred. A common regimen is 4 grams IV loading dose, followed by 1-2 grams IV per hour as a continuous infusion, or 1 gram IV every 1-4 hours. Maintenance infusion rates are often guided by serum magnesium levels.
* **Mild/Moderate (serum Mg 1.3-1.6 mg/dL or asymptomatic):** Oral magnesium can be used, with typical doses ranging from 30-60 mEq (240-480 mg elemental magnesium) per day, divided into doses. Intramuscular (IM) administration can be considered for patients unable to tolerate oral magnesium, with doses typically ranging from 4-8 grams (32-64 mEq) per day divided into 4 doses.
* **Eclampsia/Pre-eclampsia:** The widely used Pritchard regimen involves an initial IV bolus of 4 grams of magnesium sulfate over 5 minutes, followed by a continuous IV infusion of 1 gram per hour. Alternatively, IM administration can be used: 5 grams IM in each buttock initially, followed by 5 grams IM every 4 hours. Dosing may be adjusted based on seizure activity and serum magnesium levels.
* **Torsades de Pointes:** 1-2 grams IV in 10-50 mL D5W over 5-10 minutes. May repeat every 5-15 minutes. Followed by a continuous infusion of 0.5-1 gram per hour if needed.
* **Asthma (Adjunctive):** 2 grams IV in 50-100 mL NS over 15-20 minutes.
## Pediatric Dosing
Dosing is highly variable and often based on weight and indication. Exact dosing may depend on local protocol.
* **Hypomagnesemia:**
* **Acute symptomatic:** 25-50 mg/kg (elemental magnesium) IV infused over 3-60 minutes. Maximum single dose 2 grams. Maintenance infusion may be initiated at 4-10 mEq/kg/day (0.4-1.0 mEq/kg/hr), not to exceed 40 mEq/day.
* **Chronic hypomagnesemia:** Oral doses vary widely, often 100-200 mg/kg/day (elemental magnesium) divided into 4-6 doses.
* **Eclampsia/Pre-eclampsia:** Dosing regimens are similar to adults but adjusted for weight. Specific protocols should be followed.
* **Torsades de Pointes:** 25-50 mg/kg (elemental magnesium) IV infused over 10-20 minutes. Maximum single dose 2 grams.
## Dose Adjustments
* **Renal Impairment:** Magnesium is renally excreted. In patients with significant renal impairment, administer with caution and monitor serum magnesium levels closely. Reduced doses and/or extended intervals may be necessary. In severe renal impairment, avoid IV administration if possible.
## Contraindications
* Hypermagnesemia.
* Heart block (second or third degree) unless a pacemaker is in place.
* Myocardial infarction (acute phase).
* Severe renal impairment.
## Adverse Effects
Common: Flushing, sweating, hypotension, nausea, vomiting, drowsiness, decreased deep tendon reflexes.
Serious: Respiratory depression, cardiac arrhythmias, cardiac arrest, coma, hypermagnesemia.
## Key Drug Interactions
* **Neuromuscular Blocking Agents:** Magnesium can potentiate neuromuscular blockade, increasing the risk of prolonged respiratory paralysis. Use with caution and monitor respiratory status.
* **Calcium Salts:** Concurrent administration of IV calcium and magnesium can lead to precipitation and antagonize the effects of each other. Separate administration times.
* **Certain Antibiotics (e.g., aminoglycosides, tetracyclines):** Magnesium may interfere with the absorption or efficacy of these agents.
* **Nifedipine:** Concurrent use in pre-term labor has been associated with hypotension, although this is less common with IV magnesium sulfate.
## Monitoring
* **Serum Magnesium Levels:** Essential, especially with IV administration, to guide dosing and prevent toxicity. Frequency depends on clinical context and route of administration (e.g., every 4-6 hours initially for IV infusions, then less frequently as stable).
* **Renal Function:** Monitor BUN and creatinine, especially in patients with known or suspected renal impairment.
* **Vital Signs:** Blood pressure, heart rate, respiratory rate, and oxygen saturation.
* **Deep Tendon Reflexes:** Assess for loss of reflexes, an early sign of hypermagnesemia.
* **Urine Output:** Adequate urine output is important for magnesium excretion.
## Clinical Pearls
* Magnesium sulfate is administered as an anhydrous salt, but the concentration is often expressed in terms of the hydrated salt or elemental magnesium. Always clarify units when discussing doses. 1 gram of magnesium sulfate heptahydrate is equivalent to approximately 0.16 grams (160 mg) of elemental magnesium or 1.33 mEq of magnesium.
* For IV administration, magnesium sulfate should be diluted and infused slowly to prevent hypotension and other adverse effects. Rapid IV infusion can cause transient hypermagnesemia.
* IM injections can be painful; consider administering into larger muscle groups and using a larger needle.
* In patients with hypomagnesemia and hypokalemia or hypocalcemia, magnesium replacement should be addressed concurrently, as intracellular magnesium is required for normal potassium and calcium homeostasis.
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*Disclaimer: This information is intended for healthcare professionals and is not a substitute for professional medical advice. Always consult the most current prescribing information, product monographs, and relevant clinical guidelines before making any treatment decisions. Dosing and recommendations can vary significantly based on patient-specific factors and institutional protocols.*
