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SOURCE

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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.

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DEFINITION

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

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ETIOLOGY

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

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PATHOPHYSIOLOGY

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  • 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.

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EPIDEMIOLOGY

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

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PREVENTION

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  • Patients with CKD

    • Limit intake of foods with high magnesium content.

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

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RISK FACTORS

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

  • CKD

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CLINICAL PRESENTATION

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SIGNS AND SYMPTOMS
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  • 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.

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DIAGNOSIS

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MEANS OF CONFIRMATION AND DIAGNOSIS
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  • Serum magnesium >2 mEq/L (>1 mmol/L)

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LABORATORY TESTS
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  • Metabolic panel.

  • Serum magnesium.

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DIFFERENTIAL DIAGNOSIS
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DESIRED OUTCOMES

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  • Reverse neuromuscular and cardiovascular manifestations.

  • Decrease serum magnesium concentration toward normal value.

  • Identify and treat underlying cause.

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TREATMENT: NONPHARMACOLOGIC THERAPY

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  • Currently no nonpharmacologic options for the management of hypermagnesemia.

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TREATMENT: PHARMACOLOGIC THERAPY

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  • 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.

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MONITORING

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  • Evaluate serum magnesium concentration hourly when administering IV calcium until symptoms abate and magnesium concentration decreases below 3.3 mEq/L (1.64 mmol/L).

  • Continuously monitor ECG.

  • Assess urine output and for physical signs of volume overload.

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