How to manage hypomagnesemia in a patient re-feeding after a 20-day fast?

From the Guidelines

To manage hypomagnesemia in a patient re-feeding after a 20-day fast, begin with intravenous magnesium replacement using magnesium sulfate 1-2 g every 6 hours for severe deficiency (serum Mg < 1.0 mg/dL), while monitoring serum levels every 12-24 hours, as recommended by recent guidelines 1. The patient's serum magnesium level of 1.5 mg/dL indicates a moderate deficiency, which can be managed with oral supplementation using magnesium oxide 400-800 mg twice daily or magnesium citrate 300 mg 2-3 times daily. Refeeding should start at 5-10 kcal/kg for the first 24 hours, with monitoring of serum electrolytes (potassium, magnesium, and phosphorous) before the initiation of nutrition and at least every frequently for the first 3 days thereafter and longer if electrolyte abnormalities persist, as suggested by the most recent study 1. Some key points to consider in the management of hypomagnesemia in this patient include:

• Simultaneously supplement other electrolytes, particularly phosphate (20-30 mmol IV for severe deficiency) and potassium (40-80 mEq/day), as multiple electrolyte abnormalities often coexist in refeeding syndrome 1.
• Thiamine 200-300 mg daily should be administered before starting refeeding to prevent Wernicke's encephalopathy 1.
• Magnesium is essential for over 300 enzymatic reactions and proper neuromuscular function; its deficiency during refeeding occurs as insulin stimulates cellular uptake of magnesium along with glucose.
• Close cardiac monitoring is necessary as hypomagnesemia can cause arrhythmias, and frequent assessment for clinical signs of deficiency (tremors, tetany, seizures) should be performed throughout the refeeding process 1. The most recent and highest quality study 1 provides the best guidance for managing hypomagnesemia in this patient, and its recommendations should be prioritized in the development of a treatment plan.

From the FDA Drug Label

In the treatment of mild magnesium deficiency, the usual adult dose is 1 g, equivalent to 8. 12 mEq of magnesium (2 mL of the 50% solution) injected IM every six hours for four doses (equivalent to a total of 32.5 mEq of magnesium per 24 hours). For severe hypomagnesemia, as much as 250 mg (approximately 2 mEq) per kg of body weight (0. 5 mL of the 50% solution) may be given IM within a period of four hours if necessary. Alternatively, 5 g (approximately 40 mEq) can be added to one liter of 5% Dextrose Injection, USP or 0. 9% Sodium Chloride Injection, USP for slow IV infusion over a three-hour period.

The patient has a serum magnesium level of 1.5, indicating severe hypomagnesemia. The recommended dose for severe hypomagnesemia is 250 mg (approximately 2 mEq) per kg of body weight given IM within a period of four hours if necessary, or 5 g (approximately 40 mEq) added to one liter of 5% Dextrose Injection, USP or 0.9% Sodium Chloride Injection, USP for slow IV infusion over a three-hour period 2.

• The treatment should be individualized based on the patient's response and renal function.
• Caution must be observed to prevent exceeding the renal excretory capacity.
• The patient's serum magnesium level should be closely monitored during treatment.

From the Research

Management of Hypomagnesemia

To manage hypomagnesemia in a patient re-feeding after a 20-day fast, the following steps can be taken:

• Monitor serum magnesium levels closely, as hypomagnesemia can occur during refeeding, especially in patients with anorexia nervosa 3
• Measure serum magnesium on admission and recheck weekly for the first 3 weeks of refeeding as a minimum 3
• Provide prophylactic supplementation of magnesium, phosphate, and potassium to prevent refeeding syndrome, in addition to routine thiamin and multivitamin supplementation 4
• Be aware that refeeding syndrome can occur in several contexts of relative malnutrition, and that glucose-involved insulin secretion can cause abrupt reverse of lipolysis and a switch from catabolism to anabolism, leading to decreased serum levels of electrolytes such as magnesium 5

Treatment of Hypomagnesemia

• Asymptomatic patients with hypomagnesemia can be treated with oral magnesium supplements 6
• Parenteral magnesium should be reserved for symptomatic patients with severe magnesium deficiency (< 1.2 mg/dL) 6
• Establishment of adequate renal function is required before administering any magnesium supplementation 6
• Consider the potential causes of hypomagnesemia, including inadequate magnesium intake, increased gastrointestinal or renal losses, or redistribution from extracellular to intracellular space, and investigate further if necessary 6

Refeeding Syndrome

• Refeeding syndrome is a life-threatening condition that can occur in undernourished patients undergoing refeeding, and is characterized by severe electrolyte disturbances, including hypomagnesemia 7
• Early recognition and treatment of refeeding syndrome is crucial to reduce morbidity and mortality 7
• A multidiscipline nutrition team approach may be helpful in managing patients at risk of refeeding syndrome 7