Disorders of Magnesium

What is the importance of magnesium?

Important co-factor for many reactions in the body, especially in ATP dependent systems

What is the normal serum Mg range?

1.4-1.8 mEq/L

1.7-2.3 mg/dL

How do Mg disorders manifest?

As alterations in CV and neuromuscular function

Where is most filtered Mg reabsorbed?

~95% in the kidney

Mostly in LOH (~70%)

Define hypomagnesemia

Serum Mg < 1.4 mEq/L (1.7 mg/dL)

What is hypomagnesemia usually associated with?

Disorders of intestinal tract or kidney

What are GI related drug induced causes of hypomagnesemia?

Chronic PPI use, excessive laxative use

What are kidney related drug induced causes of hypomagnesemia?

Aminoglycosides, amphotericin B, cyclosporine, tacrolimus, diuretics, digoxin

What are general GI related causes of hypomagnesemia?

Reduced intake (alcohol use disorder), reduced absorption, increased loss (vomiting, diarrhea, nasogastric suction)

What are general kidney related causes of hypomagnesemia?

Tubular disorders, glomerulonephritis, pyelonephritis, hormone related, hyperthyroidism, aldosteronism

What are examples of internal redistribution that can cause hypomagnesemia?

DKA, glucose/AA/insulin administration, massive blood transfusion, pancreatitis

What are other causes of hypomagnesemia?

Excessive sweating or lactation, hypercalcemia and hypercalciuria, phosphorus depletion, extracellular volume expansion

Describe the neuro clinical presentation of hypomagnesemia

Tetany, twitching, tremor, generalized convulsions

Describe the cardiac clinical presentation of hypomagnesemia

Palpitations, arrhythmias, HTN, sudden cardiac death, EKG abnormalities

What are the treatment goals of hypomagnesemia?

Resolve symptoms, restore normal Mg levels, correct concomitant electrolyte derangements, address underlying causes

Describe IM Mg supplementation for hypomagnesemia

Painful, avoid unless severe hypomagnesemia and no IV access

Describe IV magnesium sulfate for hypomagnesemia

Avoid bolus administration

For SEVERE hypomagnesemia (< 1.0 mEq/L or s/s)

What is the amount of elemental Mg per gram of Mg sulfate?

98.6 mg elemental Mg per 1 gram of Mg sulfate

In who should IV Mg sulfate be used with caution?

Patients with concomitant hypocalcemia

What is the dosing of IV Mg sulfate for severe hypomagnesemia?

8-12 g in 50-100 mL in divided doses over 12-24 h

Followed by 4-6 g/day for 3-5 days

When should a dose of IV Mg sulfate be reduced?

Reduce by 50% in impaired renal function (CrCl < 30 mL/min)

When should oral Mg supplementation be used?

Mg > 1 mEq/L

What is a major AE of Mg supplementation?

Diarrhea

What is the most common form of oral magnesium and what is its elemental magnesium content?

Magnesium oxide

242 mg in a 400 mg tablet

How should asymptomatic mild to moderate hypomagnesemia be monitored?

Mg levels daily while hospitalized

GI side effects for oral Mg therapy

How should symptomatic/severe hypomagnesemia be monitored?

Mg levels hourly until 1.5 mEq/L, then q6-12h for next 24 hours

Mg levels daily once stable

Define hypermagnesemia

Serum Mg > 1.8 mEq/L (2.3 mg/dL)

When is hypermagnesemia seen?

Rarely seen

Most likely in CKD 4-5 as intake >> renal excretion

Critically ill patients with multi organ failure receiving EN or PN

Describe the clinical presentation of hypermagnesemia

Rarely symptomatic if serum Mg < 4.0 mEq/L (4.9 mg/dL)

What can cause hypermagnesemia?

Decreased renal excretion = AKI, CKD

Excessive intake = over treatment of eclampsia/preeclampsia, over use of Mg containing laxatives, ureteral irrigants

What are other causes of hypermagnesemia?

Lithium therapy, hypothyroidism, milk-alkali syndrome, Addison's disease, viral hepatitis, acute DKA

If symptomatic, what are the main symptoms of hypermagnesemia?

Mainly neuro and CV symptoms

Lethargy, confusion, muscle weakness, dysrhythmias

What are the treatment goals of hypermagnesemia?

Reverse neuro and CV manifestations, decrease Mg towards normal values, address underlying cause

How should hypermagnesemia be managed?

Reduce Mg intake, enhance elimination, antagonize physiologic effects of Mg

What is the treatment regimen of hypermagnesemia dependent on?

Severity

How should severe/symptomatic hypermagnesemia be treated and why?

100-200 mg IV elemental calcium (ex: 2 g calcium gluconate)

Antagonizes neuro and CV effects

Repeat hourly as needed

What supportive care should be given for severe/symptomatic hypermagnesemia?

Cardiac pacing, vasopressors, mechanical ventilation

How should hypermagnesemia be treated in individuals with normal renal function or CKD 1-3 to promote elimination of excess Mg?

Forced diuresis with 0.45% NaCl plus loop diuretics to promote removal of Mg

Dialysis for ESRD

How should severe/symptomatic hypermagnesemia be monitored?

Recheck Mg hourly until symptom resolution and Mg < 3.3 mEq/L (4.0 mg/dL)

Continuous EKG monitoring

Forced diuresis (urine output, volume overload)