Electrolyte Replacement - Magnesium

• Oral Magnesium Replacement
  

  For Mg levels greater than 1.2 mg/dL AND asymptomatic, oral therapy may be used.
  	Elemental Magnesium
  Formulary Agents	mg	mEq	Usual Dose
  MgOxide 400 mg tablets	240	20	1-2 tablets/day
  MgHydroxide (MOM) 10 ml	360	30	10-20ml/day
  MgHydroxide (Maalox) 10 ml	180	15	10-20ml/day

  Oral absorption is variable with 15-50% of a dose being absorbed. The primary adverse effect is diarrhea which may be reduced by dividing daily doses.

• Intravenous Magnesium Replacement
  Magnesium sulfate equivalencies: 1 gm MgSO4 = 100 mg Mg = 8 mEq Mg When writing orders for intravenous magnesium, specify the number of grams, not ampules. Writing orders for ampules may lead to error because there are different ampule sizes. Dosing of Intravenous Magnesium Sulfate: Weight Symptomatic or Mg less than 1.2 mg/dL Asymptomatic & Mg more than 1.2 mg/dL less than 50 kg 2-3 gm 1-2 gm more than 50 kg 3-4 gm 2-3 gm Additional doses of 1-2 gms/day of Mg Sulfate may be required for several days if the patient has not previously been receiving magnesium. Renal Insufficiency (Clcr less than 20 ml/min) may require lower doses of magnesium. Caution should be used when replacing magnesium in any patient with renal insufficiency. Maximum concentration: 1 gm in 5 ml of D5W or NS Maximum infusion rate: 1 gm over 7 minutes Magnesium sulfate may be given IM, however it can be very painful. Doses greater than 1 gm must be given in different injection sites. For symptomatic patients, bolus doses of IV magnesium are required. For asymptomatic patients, adding magnesium to the patient’s IV fluids will allow for better retention of magnesium. Repeat magnesium levels can be drawn the next day or sooner.