This document discusses hypomagnesemia, including its definition, severity classifications, evaluation, and treatment. Hypomagnesemia is defined as a serum magnesium level less than 1.7 mg/dL and can be mild, moderate, or severe. Magnesium repletion should be based on clinical manifestations and degree of hypomagnesemia. For unstable patients or cardiac arrest, intravenous magnesium is given over 1-2 minutes, while stable patients receive it over 15 minutes. Oral magnesium is used for mild asymptomatic cases.

1. HYPOMAGNESEMIA

2. unit of measurement and NORMAL RANGE
• Since the molecular weight of magnesium is 24.3 and the valence is +2,
so 1 mEq/L is equivalent to 0.50 mmol/L and to 1.2 mg/dL
mmol/L = [mg/dL x 10] ÷ mol
wt
mEq/L = mmol/L x valence
Normal range of the plasma magnesium concentration
1.4 to 1.7 mEq/L ~ 0.70 to 0.85 mmol/L ~ 1.7 to 2.1 mg/dL
Yu A S L, et al. 2019. Regulation of Magnesium Balance. UpToDate

3. cut off value for hypomagnesemia
• Hypomagnesemia is defined as a serum magnesium level <1.7 mg/dL (<0.71 mmol/L or <1.4 mEq/L)
• Mild hypomagnesemia (∼1.4–1.7 mg/dL or ∼ 0.58–0.71 mmol/L or ∼1.16–1.40 mEq/L)
• Moderate hypomagnesemia (∼1.0–1.4 mg/dL or ∼ 0.41–0.58 mmol/L or ∼ 0.82–1.16 mEq/L)
• Severe hypomagnesemia (<1.0 mg/dL or <0.41 mmol/L or <0.82 mEq/L).
Grober Uwe, et al. 2015. Magnesium in Prevention and Therapy. Nutrients 7(9), 8199-8226
Rudolph E H, et al. 2012. Nephrology Secret Chapter 80: Disorders of magnesium metabolism. Mosby, pp 560-570.
According to many magnesium researchers, the appropriate lower reference limit of the serum magnesium
concentration should be 0.85 mmol/L, especially for patients with diabetes
NHANES I identified the reference interval for serum magnesium as 0.75 mmol/L to 0.955 mmol/L with a
mean concentration of 0.85 mmol/L.

4. When should hypomagnesemia be corrected?
• All authors reviewed agree that hypomagnesemia must be corrected (level of evidence
IV, grade of recommendation D).
• Magnesium repletion should be administered based on the severity of the clinical
manifestations and the degree of hypomagnesemia (Hypomagnesemic patients usually
do not develop symptoms until serum Mg falls below 1.2 mg/dL)
• Asymptomatic patients should be treated with oral Mg supplements whenever feasible,
whereas severe hypomagnesemia (Mg < 1 mg/dL) warrants treatment with parenteral
Mg
• Serum Mg is a poor predictor of total body Mg content because only 0.3% of total body
Mg is found in serum.
• A combination of serum, urinary, and dietary Mg may the most practical method to
assess Mg status at present.
Yu A S L. 2020. Hypomagnesemia: Evaluation and Treatment. UpToDate;
Penas RD, et al. 2014. SEOM guidelines on hydroelectrolytic disorders. Clin Transl Oncol. 16(12): 1051–1059

5. IV loading of 2.4 mg/kg of lean body weight MgSO4 given over the initial four hours  Mg urine 20 h after loading
was checked
More than 60-70% of Mg is excreted in the urine
Negative  Mg deficiency is unlikely
Less than 60-70% of Mg is excreted in the urine 
Positive  Mg deficiency is likely  Should be treated
“Magnesium retention test” or “loading test”  more sensitive indicator of Mg deficiency.
Normomagnesemic magnesium depletion  isolated cellular magnesium depletion  should be considered as a
possible cause of refractory hypokalemia or unexplained hypocalcemia in patients at high risk for magnesium loss
Yu A S L. 2020. Hypomagnesemia: Evaluation and Treatment. UpToDate;
Karosanidze, Parrish CR, et al. 2014. Magnesium – So Underappreciated. Practical Gastroenterology.
NORMOMAGNESEMIC- Magnesium Depletion?

6. How urgent should we administer additional
magnesium?
Magnesium repletion should be administered based on the severity of the clinical
manifestations and the degree of hypomagnesemia
• In the acute setting, hemodynamically unstable patients (including those with
arrhythmias consistent with torsade de pointes or hypomagnesemic-hypokalemia)
should receive initial IV magnesium over 2 – 15 minutes
• In hemodynamically stable patients with severe symptomatic hypomagnesemia (such as
those with tetany, arrhythmias, or seizures), Mg concentration ≤ 1 mg/dL [0.4 mmol/L or
0.8 mEq/L]), IV magnesium can be given initially over 5 to 60 minutes followed by an
infusion
Yu A S L. 2020. Hypomagnesemia: Evaluation and Treatment. UpToDate;
Berul C I. 2020. Acquired long QT syndrome: Clinical manifestations, diagnosis, and management. UpToDate.
In patient with VF/pulseless VT cardiac arrest associated with TdP, Mg infusion occurs over 1 – 2
minutes; In patients without cardiac arrest, infusion should occur over 15 minutes.
Magnesium is not likely to be effective in terminating irregular/polymorphic VT in patients with a normal QT interval.

7. Torsa de Pointes (cardiac arrest)
& Severe Symptomatic
TdP (unstable patient)  2 gram IV bolus MgSO4 (4 mL of 50% solution mixed with D5W to
total volume of 10 mL)
• The rate of Mg infusion depends on the clinical situation.
• In patients with pulseless cardiac arrest, infusion occurs over 1 to 2 minutes. If ineffective, may repeat
immediately
• In patients without cardiac arrest, infusion should occur over 15 minutes, as rapid infusion is
associated with hypotension and asystole. If ineffective, may repeat dose up to a total of 4 g in 1 hour,
followed by infusion.
Patient with stable hemodynamic and severe symptomatic hypomagnesemia  1 to 2 grams of MgSO4 (8 to 16
mEq [4 to 8 mmol]) in 50 to 100 mL of D5W over 5 to 60 minutes, followed by an infusion.
A simple infusion regimen for non-emergent repletion is 4 to 8 g MgSO4 (32 to 64 mEq [16 to 32 mmol]) given slowly
over 12 to 24 hours (this dose can be repeated as necessary).
In the normomagnesemic - hypocalcemia, it has been suggested to repeat this dose daily for 3-5 days.
Yu A S L. 2020. Hypomagnesemia: Evaluation and Treatment. UpToDate;
Berul C I. 2020. Acquired long QT syndrome: Clinical manifestations, diagnosis, and management. UpToDate.

8. Stable Asymptomatic Hypomagnesemic Patient
Severe hypomagnesemia may require treatment with doses until 1.5 mEq/kg
• Doses < 6 g MgSO4 can be given over a period of 8–12 h
• Higher doses should be administrated over a time period > 25 h
Yu A S L. 2020. Hypomagnesemia: Evaluation and Treatment. UpToDate;
Hansen B A., et al. 2018. Hypomagnesemia in critically ill patient. Journal of Intensive Care 6:21
• Intravenous repletion in stable hospitalized patients
• Severe hypomagnesemia  4 to 8 grams of MgSO4 over 12-24 hours
• Moderate hypomagnesemia  2 to 4 grams of MgSO4 over 4 to 12 hours.
• Mild hypomagnesemia 1 to 2 grams over 1 to 2 hours.
Patients with no or minimal symptoms  If available and tolerable, oral replacement
Patients with kidney function impairment (CrCl < 30 mL/min/1.73 m )  at risk for severe
hypermagnesemia if large doses of magnesium are given  Reduce the IV Mg dose in such patients by
50% or more and closely monitoring Mg concentrations

9. Maximum Speed and Concentration that can
be given thru peripheral vein ?
• Magnesium sulphate has a high osmolarity and may cause tissue damage if it extravasates into
the surrounding tissue.
• Magnesium sulphate injection is available as 10, 20, 40 and 50% preparations
• Solutions for IV infusion (peripheral vein) must be diluted to a concentration of 20% or less
prior to administration.
• At concentrations ≥ 20% should be given via CVC.
• Maximum IV infusion rates should not exceed 2 g/h.
• When giving IV push, must dilute first and should generally NOT faster than 150 mg/minute.
• Rapid Mg administration can cause flushing, muscle weakness, or hypotension; simultaneous
volume resuscitation may be advisable.
Ayuk J., et al. 2014. Contemporary view of the clinical relevance of magnesium homeostasis. Ann Clin Biochem. Beed M, Sherman R, Mahajann R. 2013. Emergencies in critical care 2nd edition.
United Kingdom: Oxford University Press

10. 1 fl MgSO4 40% = 25 mL
40%  40 gram in 100 mL  4 gram in 10 mL  10 gram in 25 mL
2 gram (5mL) MgSO4 40% + 15 mL D5w  less than 20%
2 grams (5ml) MgSO4 40% + 15 ml 0.9% NaCl  less than 20%
2 gram (5 mL) MgSO4 40% + 5 mL D5w  20%
1 fl MgSO4 20% = 25 mL
20%  20 gram in 100 mL  2 gram in 10 mL  5 gram in 25 mL
2 grams (10ml) MgSO4 20% + 10cc D5w  less than 20%
Solutions for IV infusion (peripheral vein) must be diluted to a concentration of 20% or less
prior to administration.
At concentrations ≥ 20% should be given via CVC

11. IM ADMINISTRATION
• IM administration is also possible, but is painful and should be reserved as a last resort for
patients with no IV access.
• IM administration of the undiluted 50% solution results in therapeutic serum concentrations
in 60 min.
• 1 – 2 grams of magnesium sulphate (2–4 mL of the 50% solution) can be injected every 6 h
for 24 h (4 doses in total) IM.
Ayuk J., et al. 2014. Contemporary view of the clinical relevance of magnesium homeostasis. Ann Clin Biochem.