Pharmacy Guidelines

PHARMACY GUIDELINES Intravenous Magnesium Therapy I. Magnesium Replacement Therapy: General Information: •

Reference Magnesium Levels: 0.7-1 mmol/L or 1.7-2.43 mg/dL

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Formulary IV Magnesium Preparations: 1 mEq of Magnesium = 0.5 mmol 1 g of magnesium sulfate = 4 mmol

Salt Magnesium Sulfate 10% (100 mg/mL) Magnesium Sulfate 50% (500 mg/mL)

Elemental Magnesium 10 mg Mg++/mL

mmol Magnesium/mL 0.4 mmol

mEq Magnesium/mL 0.8 mEq

50 mg Mg++/mL

2 mmol

4 mEq

Hypomagnesaemia: Serum magnesium level of < 0.7 mmol/L. Hypomagnesaemia could be asymptomatic or symptomatic. Oral replacement is preferred in asymptomatic patients able to tolerate PO administration. Intravenous Magnesium Replacement: • All doses should be specified in mmol (mEq) • It can be give through peripheral or central venous line • Bolus dosing (i.e. 5 g over 4 hours) is acceptable if the patient is symptomatic and/or has a serum level of ≤ 0.5 mmol/L. However, bolus dosing without IV maintenance infusions provides a false sense of security because: 1. 50% of a magnesium dose is excreted in the urine. 2. Serum (Extracellular Fluid) magnesium accounts for only < 1% of total body magnesium and equilibrium between the extracellular fluid and the intracellular stores takes place very slowly. Body Weight < 50 kg > 50 kg < 50 kg > 50 kg

Symptomatic or serum level Asymptomatic or serum level < 0.5 mmol/L > 0.5 mmol/L and < 0.7 mmol/L For patients NOT currently on maintenance magnesium 16-20 mmol/day 12-16 mmol/day 20-24 mmol/day 16-24 mmol/day For patients currently on maintenance magnesium 8-12 mmol/day 4-8 mmol/day 12-16 mmol/day 8-20 mmol/day Alternate Adult Dosing Schedule 0.5 mmol/kg/day for 24 hours, then 0.25 mmol/kg/day for 3-5 days

Dilution & Infusion Rate: • May be mixed with Dextrose 5% or 0.9% sodium chloride solution • Maximum concentration of magnesium for IV use is 0.4 mmol/mL (10% solution) • Concentrations most often used is 0.02 mmol/mL (4 mmol/50 mL diluent), if bolus dosing is required. • Recommended rate: 1-8 mmol/hour (0.016-0.133 mmol/min) • Maximum rate allowed 12 mmol/hour (0.2 mmol/min) • In emergency situations only (if symptomatic hypomagnesaemia is accompanied by ventricular dysrhythmias/seizures): 10% solution may be given at a rate of 0.6 mmol/min Example: 4 mmol (2 mL) diluted to 10 mL total volume, and given over 7

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minutes Example: 12 mmol (6 mL) diluted to 50 mL total volume, and given over 20-30 minutes ICU standard Concentrations: 1. 12 mmol (3 g) in 100 mL Dextrose 5% over 2 hours 2. 16 mmol (4 g) in 100 mL Dextrose 5% over 3 hours

II. Magnesium Sulfate Dosing Guidelines for Labor and Delivery: 1. For Eclampsia Treatment and Prophylaxis: Bolus Dose: 4 gm of magnesium sulfate in 100 mL of 0.9% Sodium Chloride to run over 1 hour Maintenance Dose: Prepare 40 gm in 1000 ml of 0.9% Sodium Chloride to be run at 2g/hr (50ml/hr) 2. For Preterm Labor: Bolus Dose: 6 gm of magnesium sulfate in 100 mL of 0.9% Sodium Chloride to run over 1 hour Maintenance Dose: Prepare 40 gm in 1000 ml of 0.9% Sodium Chloride to be run at 3g/hr (75ml/hr) Precautions: •

These guidelines are not applicable in patients with renal failure; hypermagnesaemia may result • IV calcium gluconate should be readily available to reverse magnesium intoxication Monitoring: • • •

Vital signs: every 15 minutes during bolus infusion; respiration rate should be ≥ 16/min Urine output: should be ≥ 100 mL in the 4 hours preceding the dose Laboratory: magnesium level (after each dose), calcium (hypocalcaemia can cause hypomagnesaemia), potassium and phosphorus (possible intracellular ion depletion)

References: 1. 2. 3. 4. 5. 6. 7. 8.

Guidelines for Magnesium Replacement, King Faisal Specialist Hospital & Research Center Guidelines for Magnesium Replacement in Adults, Medical University of South Carolina Pharmacy Services: www.musc.edu/pharmacyservices/medusepol/Adult_Magnesium_Guidelines.pdf Magnesium Sulphate-IV Dilution, GlobalRPh Inc. http://www.globalrph.com/magnesium_dilution.htm Electrolyte Replacement Protocol, Oregon Health & Science University www.ohsu.edu/medicine/residency/handouts/pharmpearls/Nephrology/ElectrolyteReplacementP rotocol.pdf Adult Electrolyte Replacement Protocols; www.surgicalcriticalcare.net/Guidelines/electrolyte_replacement.pdf Monitored Unit Electrolyte Replacement Protocols; www.emcrit.org/misc/electrolyte_replacement.pdf Electrolyte Infusion Guidelines at University of Kentucky Hospital; http://www.hosp.uky.edu/Pharmacy/formulary/criteria/electrolyte.htm Magnesium Administration Guidelines, Massachusetts General Hospital, Department of Pharmacy & Department of Nursing Critical Care: http://www.massgeneral.org/pharmacy/icu%20Guidelines/magnesium.htm Pharmacy @ January 09