Managing hypomagnesemia: A complete guide to nursing assessment and treatment of low magnesium levels

Magnesium acts similarly to a calcium channel blocker, helping to regulate the influx of calcium to control the proper timing and duration of electrical impulses in the heart. It also plays a crucial role in stabilizing the cell membrane and maintaining the resting membrane potential. Hypomagnesemia and low magnesium levels can lead to deadly cardiac arrhythmias.

Magnesium is important in the contraction of muscles as well as their relaxation. This helps with the funcitoning of cardiac muscle tissue, the GI system, and skeletal muscle tissue. It also relaxes the smooth muscle in the vessel walls, reducing blood pressure and preventing spasms.

Magnesium is necessary for metabolism as it is a co-factor for many enzymes involved in producing ATP – the body’s primary energy source on a cellular level. It’s also involved in the regulation of glucose metabolism and insulin signaling.

Magnesium is involved in transmitting nerve impulses and coordinating muscle movements, as it helps regulate the release of neurotransmitters and the activation of ion channels.

Magnesium supports the structural integrity of bones and teeth. It is also a co-factor for enzymes that regulate bone metabolism, and low magnesium levels are associated with osteoporosis.

The body regulates its magnesium levels by adjusting how much magnesium it absorbs in the small intestine. When there are low magnesium levels, the absorption increases to prevent hypomagnesemia. The opposite is true as well!

The kidneys play a crucial role in regulating the excretion of magnesium, similar to its role in potassium.

Several hormones can influence magnesium levels. These include the Parathyroid hormone (PTH), which increases GI absorption and decreases kidney excretion. Vitamin D also stimulates magnesium absorption in the small intestines and regulates the activity of PTH.

Similar to hypokalemia, acid-base balance can also influence magnesium levels. Acidosis can cause magnesium to shift out of cells into the bloodstream and extracellular space. Alkalosis causes the opposite, leading to hypomagnesemia.

Hypomagnesemia can occur with excessive vomiting or diarrhea but occurs more often with diarrhea (it has 15x more magnesium in stool than in vomit).

Certain GI conditions that affect magnesium absorption include irritable bowel disease (IBD – AKA Crohn’s or ulcerative colitis), celiac disease, and pancreatitis.

Medications that increase magnesium loss from the GI system include chronic proton pump inhibitors (PPIs) like Omeprazole may lead to low magnesium levels. Other medications which can do this include H2 blockers, Antacids, and even laxatives.

Conditions that can lead to excessive kidney magnesium loss include renal tubular acidosis, hyperaldosteronism, and even diabetes. Certain medications can also impact this (discussed below).

Medications that can increase the excretion of magnesium in the kidneys include loop diuretics and thiazide diuretics. Other drugs that can cause hypomagnesemia include Aminoglycoside antibiotics, certain chemotherapies, calcineurin inhibitors, and Digoxin.

Chronic alcoholism can impair magnesium absorption in the small intestine and increase excretion in the urine, leading to hypomagnesemia. This magnesium wasting in the urine is reversible after four weeks of sobriety.

Patient’s with an organ transplant are more likely to experience hypomagnesemia, likely from their calcineurin inhibitor medications (like tacrolimus).

High calcium levels can lead to mildly low magnesium levels.

Certain rare genetic conditions can cause decreased magnesium absorption in the small intestine and increased renal magnesium wasting.

Like low potassium, muscle weakness is common with hypomagnesemia. They may experience fatigue and muscle weakness in their legs which can cause difficulty walking, as well as weakness of any other muscles in their body.

Patients may feel tingling sensations and experience involuntary muscle contractions, particularly in their hands or lower extremities.

As discussed above, magnesium is essential in the conduction as well as the mechanical beating of the heart. If an arrhythmia occurs, patients may experience palpitations, chest pain, shortness of breath, dizziness, or even syncope. Cardiac arrest is possible if they go into a deadly rhythm like VFIB.

Low magnesium levels can cause nausea, vomiting, or abdominal cramping. Additionally, if the patient has diarrhea, that may be a clue on the cause.

Magnesium can cause CNS hyperirritability, leading to confusion, irritability, hyperactive deep tendon reflexes, paresthesias, and seizures.

• HR: May be fast or slow, depending on any arrhythmias.
• BP: May be increased
• Respirations: usually normal
• SPO2: Usually normal
• Temp: Normal

• Muscle weakness or trouble walking or moving
• May appear fatigued or lethargic

• Auscultate for an Irregular heartbeat

• May have tender muscles
• Edema or ascites may indicate underlying kidney or liver failure
• Abdominal tenderness may be present, especially with any GI symptoms

Figuring out why the magnesium is low is essential, but there shouldn’t be any reason to delay replacing the magnesium with Oral or IV options. However, addressing the underlying cause can prevent further loss of magnesium and prevent it from happening again.

PO magnesium is the standard for mild to moderate hypomagnesemia, primarily if there are no or minimal symptoms.

There are many different variations of magnesium pills, such as:

• Magnesium Oxide: Most common and inexpensive, but it has a low absorption rate and may cause diarrhea.
• Magnesium Chloride: Has better absorption and higher bioavailability than magnesium oxide. Also less likely to cause GI side effects and may be better for skin health and wound healing.
• Magnesium Carbonate: Good for heartburn, but not the best absorption.
• Magnesium L-lactate: Less likely to cause GI symptoms like diarrhea.
• Magnesium Glycinate: Highly absorbable and less likely to cause diarrhea. It may have a calming effect on the body.
• Magnesium Citrate: Good absorption rate but also a laxative and will cause diarrhea and cramping. They are not typically used for magnesium replacement.

Generally, sustained release options are better because they minimize the renal wasting of the magnesium. Common options include:

• Magnesium Chloride 64-71.5mg elemental magnesium, 6-8 tabs in divided doses
• Magnesium L-lactate with 84mg elemental magnesium, 6-8 tabs in divided doses

If the sustained release is unavailable, magnesium oxide 800-1600mg daily in divided doses may be used, but diarrhea may occur.

IV magnesium is given to patients with severe symptoms or who are NPO for whatever reason.

IV replacement dosing will depend on the severity:

• Mild (1.6 – 1.9 mEq/L): 1-2 grams of mag sulfate over 1 – 2 hours
• Moderate (1.0 – 1.5 mEq/L): 2 – 4 grams of mag sulfate over 4 – 12 hours
• Severe (< 1.0 mEq/L): 4 – 8 grams of mag sulfate over 12 – 24 hours

Magnesium levels are generally checked at least daily while inpatient until normalization of the magnesium level.

Other electrolytes and monitoring of renal function should also be checked, usually daily, every morning.

Patients with low magnesium are at high risk for cardiac arrhythmias. Additionally, anybody receiving IV replacement with magnesium should be on a cardiac monitor.