FEN: Disorders of Magnesium Homeostasis

Question 1

What is the normal range for serum magnesium? What unit is it typically expressed in?

Answer 1

1.7-2.3 mg/dL

Question 2

Define hypomagnesemia

Answer 2

Serum magnesium less than 1.7 mg/dL

Question 3

List four principle causes of hypomagnesemia

Answer 3

1. impaired intestinal absorption
2. inadequate intake
3. hypokalemia
4. increased renal excretion

Question 4

List four cause of impaired intestinal absorption that predispose to hypomagnesemia

Answer 4

1. ulcerative colitis
2. diarrhea
3. pancreatitis
4. chronic laxative abuse

Question 5

List two conditions/care settings that predispose a patient to hypomagnesemia

Answer 5

1. Hospitalized patients

2. Alcoholism/delirium tremens

Question 6

List two electrolyte derangements commonly associated with hypomagnesemia

Answer 6

1. hypokalemia

2. hypocalcemia

Question 7

List two types of symptoms that can occur with hypomagnesemia

Answer 7

1. neuromuscular symptoms

2. cardiovascular symptoms

Question 8

List three manifestations of neuromuscular symptoms in hypomagnesemia

Answer 8

1. tetany
2. twitching
3. seizures

Question 9

List three manifestations of cardiovascular symptoms in hypomagnesemia

Answer 9

1. arrhythmias
2. sudden cardiac death
3. hypertension

Question 10

What patients are candidates for oral magnesium supplementation?

Answer 10

Asymptomatic patients

Question 11

List three options for oral magnesium supplementation

Answer 11

1. Magnesium oxide
2. Magnesium containing antacids
3. Magnesium laxatives

Question 12

What side effect typically limits oral supplementation of magnesium?

Answer 12

Diarrhea

Question 13

How should magnesium supplementation be given to nonemergency hypomagnesemia?

Answer 13

Magnesium sulfate by slow intravenous infusion

Question 14

Describe dosing of magnesium sulfate by slow intravenous infusion

Answer 14

1. 1-4 g (8-32 mEq) of magnesium sulfate

2. About 1 g/hour to avoid hypotension or increased renal excretion because of rapid administration

Question 15

If continued magnesium supplementation is required (by IV route) after initial bolus, how to dose?

Answer 15

1. 0.5 mEq/kg/day of Magnesium Sulfate added to IV fluid and administered as a continuous infusion

Question 16

How to dose adjust magnesium supplementation?

Answer 16

Reduce dose by half in patients with kidney insufficiency

Question 17

Over what time frame should magnesium replacement occur? Why?

Answer 17

1. About half of administered magnesium is excreted in the urine
2. Magnesium replacement can occur over 3-5 days

Question 18

Due to shortages of IV magnesium, for whom should use be reserved for?

Answer 18

Symptomatic patients (e.g. torsades, symptomatic hypomagnesemia)

Question 19

Define hypermagnesemia

Answer 19

Serum magnesium greater than 2.3 mg/dL

Question 20

With what chronic condition is hypermagnesemia commonly associated with?

Answer 20

Rarely occurs and is generaly associated with chronic kidney disease

Question 21

At what serum magnesium do symptoms of hypermagnesemia typically manifest?

Answer 21

Greater than 4-5 mg/dL

Question 22

List six symptoms of hypermagnesemia from least threatening to most threatening

Answer 22

1. N/V
2. Bradycardia
3. Hypotension
4. Heart block, asystole
5. Respiratory Failure
6. Death

Question 23

How to treat hypermagnesemia in asymptomatic patients with normal kidney function?

Answer 23

0.9% sodium chloride and loop diuretics

Question 24

How to treat hypermagnesemia in patients with kidney disease?

Answer 24

Hemodialysis

Question 25

What agent should be given to symptomatic patients with hypermagnesemia and why?

Answer 25

Symptomatic patients should be treated with 100-200 mg of elemental calcium administered intravenously over 5-10 minutes for cardiac stability (e.g. 2 g of calcium gluconate)

Question 26

What medications should be discontinued for all patients with hypermagnesemia?

Answer 26

Discontinue all magnesium-containing medications