Hypomagnesemia is the low concentration of magnesium on the bloodstream (normal level is 1.7-2.2mg/dL = 1.4-1.7meq/L = 0.70-0.85mmol/L). It may affect around 10% of hospitalized patients (in ICU this number may be as high as 60%).
Low levels of magnesium can cause disturbances in different organs and systems, particularly the neuromuscular and cardiovascular systems.
Different conditions can cause hypomagnesemia. These include:
Decreased intake causes:
Extracellular -> Intracellular shift causes:
Hungry bone syndrome
GI, Skin or Renal Magnesium depletion causes:
Burns affecting a large surface area
Polyuria from any etiology (diabetes, cold diuresis, recovery from AKIN)
Malabsorption syndromes (celiac disease, IBD)
Medicines (amphotericin, cisplatin, cyclosporine, diuretics, PPIs, aminoglycosides, cetuximab, matuzumab, tacrolimus, cyclosporine)
Diuretics (loop, osmotic or chronic use of thiazides)
Genetic and Inherited defects:
Autosomal-dominant hypocalcemia with hypercalciuria
Isolated dominant hypomagnesemia (IDH) with hypocalciuria
Isolated recessive hypomagnesemia (IRH) with normocalcemia
SIGNS & SYMPTOMS:
As said before, hypomagnesemia may affect different organs and systems. Below there is a list of possible signs and symptoms:
Tetany (positive Trousseau and Chvostek), spasms and muscle cramps
Seizures (tonic clonic or multifocal)
Peaking T waves
Widening of the PR interval
T wave diminution
Ventricular arrhythmias (Monomorphic or Polymorphic Ventricular Tachycardia – Torsades de pointes)
Hypokalemia (often refractory until magnesium is replaced)
Hypocalcemia (hypoparathyroidism and PTH resistance)
Hypomagnesemia is often associated with another disorders, including hypocalcemia, hypokalemia and metabolic alkalosis.
Unstable patients and patients with symptomatic hypomagnesemia (tetany, arrhythmias) may receive IV magnesium sulfate (1-2g) over 15 minutes.
If the patient is hemodynamically stable magnesium sulfate can be given IV according to the scheme below:
Severe depletion (<1mg/dL): 4-8g (32-64meq) over 12-24h.
Moderate depletion (1-1.5mg/dL): 2-4g (16-32meq) over 4-12h.
Mild depletion (1.6-1.9mg/dL): 1-2g over 1-2 hours.
As a general rule, 1g of IV magnesium may increase the serum magnesium by 0.25mg/dL.
Oral magnesium may also be used in patients (inpatient or outpatient) with magnesium depletion and in such cases, sustained or delayed release formations are preferred. Several preparations are available such as Mag-Ox 400 – containing magnesium oxide, Slow-Mag – containing magnesium chloride, and Mag-Tab containing magnesium lactate. These preparations provide 5-7 mEq (2.5-3.5 mmol or 60-84 mg) of magnesium per tablet. Six to 8 tablets should be taken daily in divided doses for severe magnesium depletion.
CKD should be monitored closely due to the risk of hypermagnesemia (lower doses may be a better idea for these patients).
The underlying disease should also be treated accordingly.
SOURCES & FURTHER READING:
- Pham PT, et al. Hypomagnesemia in Patients with Type 2 Diabetes. Clin J Am Soc Nephrol 2: 366–373, 2007.
- Fulop T. Hypomagnesemia. Medscape. Updated: Jan 04, 2016.