II. Mechanism

  1. See Magnesium

III. Indications

  1. Hypomagnesemia
  2. Arrhythmia Treatment and Prevention
    1. Torsades de Pointes
    2. Rapid Atrial Fibrillation
  3. Acute Myocardial Infarction
    1. Arrhythmia prevention (variable efficacy)
  4. Preeclampsia (Pregnancy Induced Hypertension)
  5. Preterm Labor (not effective)

IV. Contraindications

V. Preparations

  1. Oral
    1. Magnesium Oxide 400 mg tablet (61% elemental = 242 mg/tablet)
      1. Dosing: Take 2 orally daily
    2. Magnesium Hydroxide (Milk of Magnesia) 400 mg/5ml (42% elemental = 167 mg/5 ml)
      1. Dosing: 5 to 15 ml up to qid as needed for Constipation
      2. Additional: 1 ml = 0.3 mEq Magnesium
    3. Magnesium Citrate 290 mg/5ml (16% elemental = 48 mg/5ml)
      1. Dosing: Up to 1 bottle (120-300 ml)
      2. Also contains 13 mg potasssium per 5 ml
    4. Magnesium Gluconate 500 mg tablet (5% elemental = 27 mg/tablet)
      1. Dosing: 1-2 tablets orally daily
    5. Magnesium Chloride 535 mg tablet (12% elemental = 64 mg/tablet)
      1. Dosing: 2 tablets once daily
    6. Magnesium Sulfate (Epsom Salts) 98.6 mg in 1 gram salts (10% elemental)
      1. Dosing: 2-4 teaspoons in 8 oz water up to twice daily as needed for Constipation
    7. Magnesium Lactate (Mag-Tab) 84 mg tablet (12% elemental = 84 mg)
      1. Dosing: 1-2 tablets every 12 hours
    8. MagnesiumAspartate Hydroxide (Maginex) 1230 mg granules (10% elemental = 122 mg)
      1. Dosing: Take mixed in 4 ounces water up to three times daily
  2. Parenteral (IV or IM): Magnesium Sulfate (MgSO4)
    1. Magnesium Sulfate is 10% elemental (1 gram Magnesium per 100 ml solution)
    2. One gram MgSO4 contains 8.12 meq Magnesium
    3. One ml MgSO4 50% Solution = 4 meq Magnesium
    4. One ml MgSO4 10% Solution = 0.8 meq Magnesium

VI. General Pointers

  1. Do NOT exceed 100 meq/day
  2. Adjust replacement for decreased Renal Function

VII. Dosing: Oral

  1. Constipation
    1. See oral preparations above for dosing
    2. Most common use of Magnesium containing compounds
  2. Recommended Daily Allowance (adults)
    1. Women: 310 mg/day (320 mg/day if over age 30 years)
    2. Men: 400 mg/day (420 mg/day if over age 30 years)
  3. Magnesium Deficiency
    1. No standardization for diagnosis or for oral replacement
  4. Migraine Headache Prophylaxis (single study from Germany)
    1. Trimagnesium Dicitrate 600 mg orally daily
    2. Peikert (1996) Cephalgia 16(4): 257-63 [PubMed]

VIII. Dosing: IV Dosing of Magnesium Sulfate

  1. Replacement of documented Magnesium deficiency
    1. MgSO4 0.5-1.0 grams/hour (4-8 meq/hour) for 24 hours
  2. Preeclampsia or Pregnancy Induced Hypertension
    1. Preparation
      1. Magnesium Sulfate 5 grams in 250 ml D5W (20 mg/ml)
      2. Final concentration: 2 grams/hour = 100 ml/hour
    2. Load: 4-6 grams MgSO4 in 100 ml IV over 20-30 minutes
    3. Maintenance: 2-3 grams MgSO4 per hour
    4. Continue until diuresis or about 24 hours postpartum
    5. See monitoring in obstetrics below
  3. Preterm Labor (not effective)
    1. Same doses as in Preeclampsia
    2. Does not prevent preterm birth
      1. Gyetvai (1999) Obstet Gynecol 94:869-77 [PubMed]
  4. Maintenance in prolonged IV fluid
    1. Add 1-2 grams (2-4 ml 50% MgSO4) to total IVF per day
    2. Delivers 0.3 to 0.7 meq per hour
  5. Arrhythmia
    1. Prepare 1-2 grams (2-4 ml 50% MgSO4) in 10 ml D5W
    2. Ventricular Tachycardia: 1-2 g MgSO4 IV over 1-2 min
    3. Ventricular Fibrillation: 1-2 g MgSO4 IV Push
    4. Torsades de Pointes: 1-2 g (up to 10 g) MgSO4 IV
    5. Atrial Fibrillation: 1.2 to 2 grams over 30 minutes
  6. Asthma
    1. Single dose: 25-50 mg/kg for acute severe Asthma Exacerbation in age under 18 years

IX. Drug Interactions

  1. Increased Magnesium levels with drugs that reduce urinary excretion
    1. Calcitonin
    2. Glucagon
    3. Potassium-Sparing Diuretics
  2. Drugs with absorption effected by concurrent Magnesium
    1. Aminoglycosides
    2. Bisphosphonates
    3. Calcium Channel Blockers
    4. Fluoroquinolones
    5. Skeletal Muscle Relaxants
    6. Tetracyclines

X. Adverse Effects (see level related effects below)

  1. See Hypermagnesemia
  2. Too rapid Magnesium Sulfate administration
    1. Flushing
    2. Sweating
    3. Mild Bradycardia
    4. Hypotension

XI. Monitoring: Obstetrics protocol in Severe Preeclampsia

  1. Vital Signs and Reflexes
    1. First hour: Check every 15 minutes
    2. Later: Monitor Vital Signs every hour
  2. Intake and Urine output
    1. Consider Foley Catheter
    2. Fluid restrict to 2400 cc per 24 hours
  3. Examination
    1. Mental status
    2. Lung Exam and Respiratory Rate
    3. Urine output
    4. Deep Tendon Reflexes
  4. Check Serum Magnesium Level
    1. See also Serum Magnesium and Hypermagnesemia
    2. Obtain 6 hours and 12 hours after MgSO4 load (and then every 6 hours)
    3. Serum Magnesium level indications (not indicated in normal Renal Function, DTRs, normal urine output)
      1. Absent Deep Tendon Reflexes
      2. Decreased urine output
      3. Elevated Serum Creatinine
  5. Indications to stop Magnesium and check level immediately
    1. Urine output <30 ml/hour
    2. Respiratory Rate <12 per minute
    3. Loss of Deep Tendon Reflexes

XII. Management: Antidote for Magnesium Toxicity

  1. Calcium Gluconate 1 gram IV slowly over 2-3 minutes

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