Hypermagnesemia

SOURCE

Source: Flurie RW, Brophy DF. Disorders of potassium and magnesium homeostasis. In: DiPiro JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM, eds. Pharmacotherapy: A Pathophysiologic Approach. 10th ed. New York, NY: McGraw-Hill; 2017. http://accesspharmacy.mhmedical.com/content.aspx?bookid=1861&sectionid=134127639. Accessed March 31, 2017.

DEFINITION

• Serum magnesium >2 mEq/L (>1 mmol/L, >2.4 mg/dL)

ETIOLOGY

• Caused by decreased renal excretion or excessive intake of magnesium.

PATHOPHYSIOLOGY

• Magnesium concentrations steadily increase as glomerular filtration rate (GFR) decreases below 30 mL/min/1.73 m² (0.29 mL/s/m²).

  • Important for patients to maintain normal diet.

• Critically ill patients with multi-organ failure receiving enteral or parenteral nutrition.

EPIDEMIOLOGY

• Rarely occurs except with stage 4 or 5 chronic kidney disease (CKD).

PREVENTION

• Patients with CKD

  • Limit intake of foods with high magnesium content.

  • Avoid long-term use of magnesium hydroxide and magnesium sulfate.

RISK FACTORS

• Age: elderly prone to hypermagnesemia due to reduced GFR and use of magnesium-containing antacids and vitamins.

• CKD

CLINICAL PRESENTATION

SIGNS AND SYMPTOMS

• Symptoms rare with serum magnesium concentration <4 mEq/L (<2 mmol/L)

• Sequence of neuromuscular signs as serum magnesium increases from 5 mEq/L to 12 mEq/L (2.5–6 mmol/L):

  • Sedation.

  • Hypotonia.

  • Hyporeflexia.

  • Somnolence.

  • Coma.

  • Muscle paralysis.

  • Respiratory depression.

• Sequence of cardiovascular signs as serum magnesium increases from 3 to 15 mEq/L (1.5–7.5 mmol/L):

  • Hypotension.

  • Cutaneous vasodilation.

  • QT-interval prolongation.

  • Bradycardia.

  • Primary heart block.

  • Nodal rhythms.

  • Bundle branch block.

  • QRS- and then PR-interval prolongation.

  • Complete heart block.

  • Asystole.

DIAGNOSIS

MEANS OF CONFIRMATION AND DIAGNOSIS

• Serum magnesium >2 mEq/L (>1 mmol/L)

LABORATORY TESTS

• Metabolic panel.

• Serum magnesium.

DIFFERENTIAL DIAGNOSIS

• Hyperkalemia

DESIRED OUTCOMES

• Reverse neuromuscular and cardiovascular manifestations.

• Decrease serum magnesium concentration toward normal value.

• Identify and treat underlying cause.

TREATMENT: NONPHARMACOLOGIC THERAPY

• Currently no nonpharmacologic options for the management of hypermagnesemia.

TREATMENT: PHARMACOLOGIC THERAPY

• Treatment regimen depends on severity of signs and symptoms and degree of serum magnesium concentration elevation.

• Options:

  • Reduce magnesium intake.

  • Enhance magnesium elimination.

    • Forced diuresis with saline and loop diuretics (eg, furosemide 40 mg IV) in patients with normal renal function or stage 1, 2, or 3 CKD

  • Antagonize physiologic effects.

    • IV calcium (100–200 mg of elemental calcium; eg, calcium gluconate 2 g IV)

      • Repeat hourly in life-threatening situations.

MONITORING

• Evaluate serum magnesium concentration hourly when administering IV calcium until symptoms abate and ...