II. Mechanism

  1. See Magnesium

III. Indications

IV. Contraindications

V. Preparations

  1. Dietary Sources (maintenance of daily needs)
    1. Green leafy vegetables (e.g. spinach)
    2. Legumes (e.g. soy milk, black beans, edamame)
    3. Nuts (e.g. almonds, cashews, peanuts, peanut butter)
    4. Seeds (e.g. pumpkin seeds, chia seeds)
    5. Whole grains (e.g. shredded wheat cereal, brown rice)
    6. Baked potato with skin
  2. Oral
    1. Magnesium Oxide (Mag-Ox)
      1. Preparation: 400 mg tablet (61% elemental = 242 mg/tablet)
      2. Dosing: Take 2 orally daily
      3. Less well absorbed than other oral forms, but least expensive
    2. Magnesium Hydroxide (Milk of Magnesia)
      1. Preparation: 400 mg/5ml (42% elemental = 167 mg/5 ml)
      2. Dosing: 5 to 15 ml up to qid as needed for Constipation
      3. Additional: 1 ml = 0.3 mEq Magnesium
    3. Magnesium Citrate
      1. Preparation: 290 mg/5ml (16% elemental = 48 mg/5ml)
      2. Dosing: Up to 1 bottle (120-300 ml)
      3. Also contains 13 mg potasssium per 5 ml
      4. Most common form used in Constipation
    4. Magnesium Gluconate
      1. Preparation: 500 mg tablet (5% elemental = 27 mg/tablet)
      2. Dosing: 1-2 tablets orally daily
    5. Magnesium Chloride (SlowMag)
      1. Preparation: 535 mg tablet (12% elemental = 64 mg/tablet)
      2. Dosing: 2 tablets once daily
    6. Magnesium Sulfate (Epsom Salts)
      1. Preparation: 98.6 mg in 1 gram salts (10% elemental)
      2. Dosing: 2-4 teaspoons in 8 oz water up to twice daily as needed for Constipation
    7. Magnesium Lactate (Mag-Tab)
      1. Preparation: 84 mg tablet (12% elemental = 84 mg)
      2. Dosing: 1-2 tablets every 12 hours
    8. Magnesium Aspartate Hydroxide (Maginex)
      1. Preparation: 1230 mg granules (10% elemental = 122 mg)
      2. Dosing: Take mixed in 4 ounces water up to three times daily
  3. 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. Precautions

  1. Avoid routinely supplementing >100 mEq/day (outside of Magnesium Replacement and other indications)
  2. Avoid "fad" supplementation for non-indications without evidence (e.g. energy, Insomnia, Leg Cramps)
  3. Adjust replacement for decreased Renal Function
  4. Serum Magnesium levels considerably and are unreliable as 99% of Magnesium is intracellular
    1. Hypokalemia is a better marker for Hypomagnesemia (low Potassium suggests low Magnesium)

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
    2. Magnesium Oxide 400-800 mg tablet orally, and recheck labs after 60 minutes
  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. Magnesium Sulfate replacement given at rate of 1-2 grams/hour
    2. Serum Magnesium 1.6 to 1.9 mEq/L: Give 1-2 grams Magnesium Sulfate IV
    3. Serum Magnesium 1.0 to 1.6 mEq/L: Give 2-4 grams Magnesium Sulfate IV
    4. Serum Magnesium <1.0 mEq/L: Give 4-8 grams Magnesium Sulfate IV
    5. Recheck Serum Magnesium at 30-60 minutes after infusion
  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. Diarrhea
  3. 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

XIV. References

  1. Hayes and Swaminathan in Herbert (2021) EM:Rap 21(5): 7-9
  2. Guerrera (2009) Am Fam Physician 80(2): 157-62 [PubMed]
  3. (2022) Presc Lett 29(7): 40

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Related Studies

Cost: Medications

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Ontology: Magnesium Chloride (C0024472)

Definition (NCI) Magnesium Chloride was used as a laxative. An alkaline earth metal, magnesium is important for many biochemical functions and reactions; for bone and muscle function, protein and fatty acid formation, activation of B vitamins, blood clotting, insulin secretion, and ATP formation. More than 300 enzymes require magnesium for catalytic action. The adult daily requirement is about 300 mg/day. Magnesium is found in many green plants, vegetables, and seeds; chlorophyll is a magnesium-centered porphyrin compound. Magnesium salts are used for magnesium deficiency supplementation. (NCI04)
Definition (MSH) Magnesium chloride. An inorganic compound consisting of one magnesium and two chloride ions. The compound is used in medicine as a source of magnesium ions, which are essential for many cellular activities. It has also been used as a cathartic and in alloys.
Concepts Pharmacologic Substance (T121) , Inorganic Chemical (T197)
MSH D015636
SnomedCT 45733002
English Chloride, Magnesium, MgCl2, Magnesium chloride (MgCl2), Magnesium Chloride, magnesium chloride (medication), mineral supplements magnesium chloride, magnesium (as magnesium chloride), MAGNESIUM CHLORIDE, Magnesium Chloride [Chemical/Ingredient], mgcl2, magnesium chloride, Magnesium chloride, Magnesium chloride (substance)
French MgCl2, Chlorure de magnésium
Swedish Magnesiumklorid
Czech chlorid hořečnatý
Finnish Magnesiumkloridi
Japanese 塩化マグネシウム
Italian MgCl2, Cloruro di magnesio
Polish Chlorek magnezowy
Norwegian Magnesiumklorid, MgCl2
Spanish cloruro de magnesio (sustancia), cloruro de magnesio, Cloruro de Magnesio
German Magnesiumchlorid
Portuguese Cloreto de Magnésio

Ontology: Magnesium Oxide (C0024477)

Definition (NCI) The oxide salt of magnesium with antacid, laxative and vascular smooth muscle relaxant activities. Magnesium combines with water to form magnesium hydroxide which reacts chemically to neutralize or buffer existing quantities of stomach acid; stomach-content and intra-esophageal pH rise, resulting in a decrease in pepsin activity. This agent's laxative effect is the result, in part, of osmotically mediated water retention, which subsequently stimulates peristalsis. In addition, magnesium ions may behave as calcium antagonists in vascular smooth muscle.
Definition (MSH) Magnesium oxide (MgO). An inorganic compound that occurs in nature as the mineral periclase. In aqueous media combines quickly with water to form magnesium hydroxide. It is used as an antacid and mild laxative and has many nonmedicinal uses.
Concepts Pharmacologic Substance (T121) , Inorganic Chemical (T197)
MSH D008277
SnomedCT 66389008, 419521006
English Magnesium Oxide, Oxide, Magnesium, Magnesia, Magnesium oxide (MgO), mineral supplements magnesium oxide, magnesium oxide (medication), MAGNESIUM OXIDE, Magnesium Oxide [Chemical/Ingredient], mag oxide, magnesia, magnesium oxides, mag-oxide, magnesium oxide, Mag-Oxide, Magnesium oxide, Magnesium oxide (substance), MAGNESIA, MAGNESIUM (AS OXIDE), Magnesium oxide (product)
Spanish óxido de magnesio (producto), óxido de magnesio (sustancia), óxido de magnesio, Óxido de Magnesio
French Magnésie, Oxyde de magnésium
Swedish Magnesiumoxid
Czech oxid hořečnatý
Finnish Magnesiumoksidi
Italian Magnesia, Ossido di magnesio
Polish Tlenek magnezu, Tlenek magnezowy
Japanese 酸化マグネシウム, 苦土
Norwegian Magnesiumoksid
German Magnesiumoxid
Portuguese Óxido de Magnésio

Ontology: Magnesium Sulfate (C0024480)

Definition (NCI_NCI-GLOSS) A drug used to treat pre-eclampsia and eclampsia (serious complications of pregnancy). Magnesium sulfate is also being studied for its ability to prevent the toxic side effects of certain drugs used to treat colorectal cancer. It is a type of anticonvulsant agent.
Definition (MSH) A small colorless crystal used as an anticonvulsant, a cathartic, and an electrolyte replenisher in the treatment of pre-eclampsia and eclampsia. It causes direct inhibition of action potentials in myometrial muscle cells. Excitation and contraction are uncoupled, which decreases the frequency and force of contractions. (From AMA Drug Evaluations Annual, 1992, p1083)
Concepts Inorganic Chemical (T197) , Pharmacologic Substance (T121)
MSH D008278
SnomedCT 37400007, 387202002
English Magnesium Sulfate, Sulfate, Magnesium, Sulfuric acid magnesium salt (1:1), magnesium sulfate (medication), mineral supplements magnesium sulfate, Magnesium Sulfate [Chemical/Ingredient], MAGNESIUM SULFATE, magnesium sulphate, magnesium sulfates, Magnesium Sulfate, Unspecified, MAGNESIUM SULFATE, UNSPECIFIED, magnesium sulfate, Magnesium Sulfate whiskers, Magnesium sulfate, Magnesium sulphate, Magnesium sulfate (product), Magnesium sulfate (substance), Magnesium SO4, MAGNESIUM (AS SULFATE)
French Sulfate de magnésium, MgSO4
Swedish Magnesiumsulfat
Czech síran hořečnatý
Finnish Magnesiumsulfaatti
Japanese 硫酸マグネシウム
Polish Siarczan magnezowy
Norwegian Magnesiumsulfat
Spanish sulfato de magnesio (producto), sulfato de magnesio (sustancia), sulfato de magnesio, Sulfato de Magnesio
German Magnesiumsulfat
Italian Solfato di magnesio
Portuguese Sulfato de Magnésio

Ontology: MAGNESIUM GLUCONATE (C0126777)

Concepts Pharmacologic Substance (T121) , Organic Chemical (T109)
MSH C030691
SnomedCT 116126005
English magnesium gluconate (medication), mineral supplements magnesium gluconate, magnesium (as gluconate), MAGNESIUM GLUCONATE, Magnesium Gluconate, magnesium gluconate, Magnesium gluconate (substance), Magnesium gluconate, MAGNESIUM (AS GLUCONATE)
Spanish gluconato de magnesio (sustancia), gluconato de magnesio

Ontology: Magnesium Aspartate (C0543448)

Concepts Pharmacologic Substance (T121) , Amino Acid, Peptide, or Protein (T116) , Biologically Active Substance (T123)
MSH D001224
SnomedCT 421128005, 421363009
English Aspartate, Magnesium, Magnesium aspartate (product), Magnesium aspartate (substance), Magnesium aspartate, magnesium aspartate, MAGNESIUM ASPARTATE, Aspartic Acid, Magnesium (2:1) Salt, Magnesium ASpartate, Magnesium Aspartate
Spanish aspartato de magnesio (sustancia), aspartato de magnesio (producto), aspartato de magnesio

Ontology: Magnesium lactate (C0717900)

Concepts Pharmacologic Substance (T121) , Organic Chemical (T109)
SnomedCT 116129003
English magnesium lactate, MAGNESIUM LACTATE, magnesium (as lactate), Magnesium lactate, Magnesium lactate (substance)
Spanish lactato de magnesio (sustancia), lactato de magnesio

Ontology: Magnesium supplements (C3540792)

Concepts Pharmacologic Substance (T121) , Inorganic Chemical (T197)
English Magnesium, Magnesium supplements