6 - Magnesium Disorders

Question 1

Physiological Roles of

MAGNESIUM

Answer 1

COFACTOR for many enzymatic reactions
ATPase // Glycolysis

Protein Biosynthesis

Metabolism
of Nucleotides / Ca2+ / K+ / energy

Regulator of ION CHANNELS + TRANSPORTERS
in EXCITABLE tissues

Question 2

Normal Serum Concentration

MAGNESIUM

Answer 2

1.7 - 2.4 mg/dL

*note we use mg/dl , a lot LOWER concentration in the body

Question 3

Mag GI Absorption

Answer 3

only 30-35% absorbed

POOR ABSORPTION
VVV
So PO admin is NOT good to increase mag levels

Need a Good KIDNEY

Question 4

Controlling Factors for Magnesium

Answer 4

just the KIDNEY

there is NO Hormone that actively affects magnesium
just Passive diffusion:

Proximal:
Follows Na+ // Water

• *Ascending:**
• *Ca+ // Mag Interaction**

Question 5

HypoMagnesemia

Serum level

Answer 5

<1.7 mg/dL

Normal is
1.7-2.4

Question 6

HypoMagnesemia
ETIOLOGY

Answer 6

MALNUTRITION = very COMMON

KetoACIDOSIS / HYPERaldosteronism / HYPERcalcemia / HypoPhosphotemia

REFEEDING Syndrome
Malnourished –> REFED –> use up ALL the MAG when fed

BLOOD TRANSFUSION
Citrate binds to Magnesium

• Decreased GI absorption*
• *Surgery** // Radiation Enteritis / Pancreatic insufficiency
• *Increased GI losses**
• *Chronic Diarrhea /** EXCESSIVE LAXATIVE USE

Renal Losses
Burns / Sweating / Chronic Alcholism

Question 7

Medications that can cause:
HypoMagnesemia

Answer 7

RENAL LOSSES

Osmotic Agents

Thiazide / Furosemide / Bumetanide

Aminoglycosides / Cyclosporin

Digoxin / Tacrolimus

Amphotericin B

Question 8

HypoMagnesemia
S/Sx

Moderate = <1.5

Severe = <1.2

Answer 8

Typically MASKED by PRIMARY disease states
(potassium or calcium issues)
but there are 2 symptoms that we can use to DISTINGUISH

MUSCLE FASCICULATIONS
Twitching

TORSADE DE POINTES
life threatening –> need to be treated IMMEDIATELY

Neuromuscular / Neurologic / Psychiatric / Cardiac / Electrolyte

Question 9

Mechanism of HypoMagnesmia
S/Sx

Answer 9

Neurological Symptoms
NMDA receptor stimulation

Cardiovascular Symptoms
Induce depolarization via EC movement of K+
related to serum DECREASE of K+

Neuromuscular Symptoms
INCREASE Ca binding + release
related to decrease of serum Ca2+

Question 10

Cardiac Symptoms
of HypoMagnesemia

Answer 10

Arrhythmias
Ventricular / SVT / Digoxin Toxicity
TORSADES DE POINTES
(widening QRS complex)

Heart Failure

HYPERtension

Coronary Artery Vasospasms

Question 11

Mild / Moderate Asymptomatic
HypoMagnesmia

Answer 11

• *Mild**
• *1.5 - 1.6** mg/dL
• *Moderate**
• *1.2-1.4** mg/dL
• *Treat Both Similarly:**
• *Diet // Oral Supplement // Parenteral**

Question 12

TREATMENT FOR
Severe OR Symptomatic

HypoMagnesmia

<1.2 mg/dL

Specifically, if life threatening = severe:
LOOK AT EKG for TORSADES DE POINTES

Answer 12

Treat with:
PARENTERAL MAG
2 GM Q15 min
4-8 gm / 100ml D5W or 0.9NS

Continous Infusion > IVPB > IM/IVP is okay too

Question 13

HypoMagnesmia
DIET TREATMENT

Answer 13

Nuts

Green Veggies

Whole Grain Cereal

MEAT

Mild or Moderate Asymptomatic
1.5-1.6 // 1.2-1.4

Question 14

HypoMagnesemia
DOSE of Oral Treatment

NUTS / GREEN VEGGIES / CEREAL / MEAT

Highest Elemental Mag:
OXIDE > Hydroxide > GLuconate > Chloride

Answer 14

300-600mg ELEMENTAL Mag Daily
various salt forms, look at the Elemental Mag
Dosed FOUR TIMES A DAY
because of poor GI absorption

SLOW onset of ACTION

ADR:
DIARRHEA // N/V

Question 15

Mild / Moderate HypoMagnesemia

• *PARENTERAL TREATMENT**
• typically only give IV if LIFE THREATENING = TDP*

Answer 15

@1 gm / hr

We have to give it SLOW, b/c kidney will eliminate it if fast
& HypoTension

Mild = 1.5-1.6
1-2 gm/ 100mL
Mag SulfateinD5Wor0.9NS

Moderate = 1.2 - 1.4
2-4 gm/100ml

1gm Mg Sulfate = 8.12 mEq elemental Mg

Question 16

Parenteral Magnesium Supplement

Routes of Admin + ADR

Answer 16

Parenteral Dose is 30-50% of ORAL Dose
Since Oral dose is lost due to poor GI absorption

CONTINUOUS INFUSION
Can exceed renal threshold // HypoTension (<1g/hour)

IVPB is also possible

IM - Painful

IVP - Flushing / Sweating / Warm Sensation

Question 17

HYPERmagnesemia

Levels

Answer 17

>2.4 mg/dL

Normal is:
1.7-2.4

Question 18

CAUSES of HYPERmagnesemia

not as Common as HypoMagnesemia

Answer 18

EXCESSIVE MAGNESIUM INTAKE
(MOST COMMON)
Antacids // Cathartics (especially with CKD)

• *GFR < 30 mL/min**
• *POOR KIDNEY FUNCTION**

Lithium Therapy

HypoThyroidism

Addison’s Disease
treatment of Eclampsia

Question 19

HYPERMagnesemia

S/Sx

Answer 19

Most Sympsoms come from

• *Calcium / Potassium disorders**
• Except for:*

Cardiac
CUTANEOUS VASODILATION

Neuromuscular
HypoReflexia // Muscle Paralysis

Symptoms may occur when:
Moderate = 4.1 - 12.5 mg/dL
Severe = >12.5 - 32 mg/dL

Question 20

Mild / Moderate Asymptomatic
HYPERmagnesemia

Treatment Algorithm

Answer 20

• *Mild Asymptomatic**
• *2.5 - 4 mg/dL**
• *Moderate Asymptomatic**
• *4.1 - 12.5 mg/dL**

Same Treatment, NO DRUGS that SPECIFICALLY REMOVE MAG
Saline Infusion
Furosemide
Hemodialysis

Question 21

Severe OR Symptomatic
HYPERMagnesemia

Treatment Algorithm

Answer 21

LIFE THREATENING
Muscle Paralysis / Cutaneous Vasodilation

>12.5 mg/dL

Calcium
to FIX EKG

Saline Infusion

Hemodialysis

Question 22

HYPERmagnesemia
TREATMENT

Answer 22

• *Mg Restriction**
• no drugs to DIRECTLY remove MAG*

CALCIUM Cl or Glu
this is for the CV effects = EKG Change
1gm over 5-10 min
(HYPERK is 1gm over 2-3 min)

Furosemide

Saline Diuresis = 0.9% NaCl
To introduce MORE sodium to kidneys –> eliminate both Mag + Na+

Hemodialysis
if poor kidney fxn

Question 23

How to treat SEVERE HypoMagnesemia

<1.2 + Symptoms

Answer 23

4-8 gm/100ml

Mag Sulfate in D5W or 0.9Ns

@2gm q15min

then SLOW DOWN
1gm / 1 hour
for the rest of the mag

Question 24

Which Electrolytes affect MAGNESIUM’s
Excretion & Reabsorption?

Answer 24

Mag mainly follows SODIUM

↓ CALCIUM = Neuromuscular
Modulates Ca2+ binding and release from the sarcoplasmic reticulum (SR)
Interaction w/ Mag+Calcium in ASCENDING loop

POTASSIUM = ↓K
Blocks outward movement of K+ through K+ channels in cardiac cells