Patients with cancer may experience low levels of magnesium and potassium for a variety of reasons throughout the course of their treatment, and both conditions can be serious or even fatal. Oncology nurses are critical in educating patients and understanding the benefits and potential concerns associated with electrolyte replacement, Puja Patel, PharmD, BCOP, from Northwestern Medicine Delnor Cancer Center in Geneva, IL, said during a session during the ONS BridgeTM virtual conference on September 16, 2021.
Magnesium is a mineral component of the bony skeleton that assists in energy transfer; insulin release; protein, carbohydrate, and fat metabolism; maintenance of normal cell membrane and function; and regulation of parathyroid hormone secretion. Patients with hypomagnesemia experience nausea, vomiting, decreased appetite, muscle cramps, and abnormal heart rhythms.
Hypomagnesemia may stem from alcohol use, gastrointestinal (GI) losses, and renal losses. Medications such as anti-infectives, antiviral agents, bisphosphonates, bowel stimulants, diuretics, immunosuppressive agents, and proton pump inhibitors may also cause hypomagnesemia, as well as chemotherapy agents. To evaluate for hypomagnesemia, assess patients’ nutritional intake, alcohol intake, surgical history, and history of diabetes, cardiac, endocrine, GI, and renal disorders as well as medications.
Patel said that the most significant clinical manifestation of severe hypomagnesemia involves the neurologic system.
“Magnesium is vital for most metabolic functions in the body. When there are changes in adenosine triphosphate and energy, the neuromuscular system tells us,” Patel explained. “Cardiac dysrhythmias don’t occur because of cardiovascular abnormalities but rather neuromuscular irritability.”
Diagnostic tests include blood and urine screenings, and an electrocardiogram may be needed. If hypomagnesemia is diagnosed, identifying and treating potential underlying causes are the first approach. In mild cases, dietary adjustments may suffice, and good sources include:
- Dairy, such as low-fat yogurt
- Fruits, such as prune juice
- Vegetables, such as artichokes and spinach
- Nuts and seeds
Magnesium can be replenished through IV infusion, but Patel said, “Up to 50% of infused magnesium is excreted in the urine. Thus, a constant, slow infusion provides better repletion than bolus infusion.” Oral administration is best with a sustained-release formula.
Oral magnesium replacement can lead to diarrhea, weakness, and fatigue, although magnesium chloride and magnesium lactate are less likely to cause diarrhea. Nurses should prepare patients for the possibility of hypomagnesemia and discuss early signs and symptoms.
Depletion of magnesium also promotes the renal loss of potassium, an electrolyte that is integral in nerve impulse transmission, muscle contraction, and cardiac function. The body does not store potassium and requires 40–60 mEq per day.
The most common causes of cancer-induced hypokalemia are malnutrition and malabsorption due to cancer bowel infiltration or obstruction, Patel said. Cancer treatments causing diarrhea or vomiting, as well as concomitant drugs, an imbalance in magnesium, and renal tubular dysfunction also can cause hypokalemia.
Patients should be counselled to include potassium-rich foods in the diet. Good sources include:
- Whole grains
As with hypomagnesemia, nurses should prepare patients for signs such as nausea, vomiting, excessive urination, constipation, muscle weakness, leg cramps, and palpitations. Patients also may have fatigue, depression, confusion, or general malaise. Severe hypokalemia can lead to hypoventilation and hypotension.
In addition to dietary support, patients can be given oral potassium replacements or via IV infusion if needed. When administered via IV, potassium must be diluted in sodium chloride, and it cannot be given as an IV push, as this can be fatal. Potassium is absorbed via the GI tract and can result in GI irritation as well as indigestion and nausea. Administering with a full glass of water or just after meals may help prevent those side effects.