How does prolonged MiraLAX (polyethylene glycol) use cause electrolyte disorders, such as hypernatremia or hypokalemia?

From the Guidelines

Prolonged use of MiraLAX can lead to electrolyte disorders due to its osmotic effect, causing excessive loss of electrolytes like sodium, potassium, magnesium, and calcium in the stool, as evidenced by the mechanism of action of osmotic laxatives like macrogols (polyethylene glycol) 1. The primary concern with prolonged MiraLAX use is its potential to disrupt electrolyte balance, particularly in vulnerable populations. MiraLAX, being an osmotic laxative, increases the amount of water in the large bowel by drawing fluid from the body into the bowel or by retaining the fluid that was administered, which can prevent proper absorption of essential electrolytes in the colon. Some key points to consider include:

• The osmotic action of MiraLAX can lead to the depletion of electrolytes like sodium, potassium, magnesium, and calcium in the bloodstream, as these are not properly absorbed in the colon due to the increased water content 1.
• Symptoms of electrolyte imbalances may include muscle weakness, irregular heartbeat, confusion, and in severe cases, seizures, highlighting the importance of monitoring electrolyte levels, especially in high-risk patients.
• For those requiring long-term laxative therapy, using the lowest effective dose of MiraLAX, considering periodic breaks from the medication if possible, and having electrolyte levels monitored regularly through blood tests are advisable strategies to mitigate the risk of electrolyte disorders, especially when using doses higher than the standard 17g daily recommendation or for longer than 2 weeks continuously. It is crucial to weigh the benefits of MiraLAX against the potential risks, particularly in patients with pre-existing conditions that may exacerbate electrolyte imbalances, and to consider alternative laxative options or prokinetic agents like prucalopride, which may have a different side effect profile 1.

From the Research

Prolonged Miralax Use and Electrolyte Disorders

• Prolonged use of Miralax, a polyethylene glycol (PEG) based laxative, can lead to electrolyte disorders due to its mechanism of action as an osmotic laxative 2, 3.
• Miralax works by increasing the amount of water in the stool, which can lead to an imbalance of electrolytes, including sodium, potassium, and chloride, in the body 4, 3.
• Studies have shown that PEG-based laxatives, including Miralax, can cause changes in serum electrolyte levels, particularly in patients with underlying medical conditions or those taking certain medications 5, 4.
• The use of PEG-based laxatives without electrolytes can lead to a greater risk of electrolyte imbalances, particularly hyponatremia (low sodium levels) 2, 3.
• Factors that increase the risk of electrolyte disorders with prolonged Miralax use include:
  • Underlying medical conditions, such as kidney disease or heart failure 5
  • Use of certain medications, such as thiazide diuretics or SSRIs 5
  • Advanced age 5, 2
  • Inadequate monitoring of electrolyte levels 5, 4

Mechanism of Electrolyte Imbalance

• The renin-aldosterone system becomes activated due to the loss of fluid, leading to oedema and acute weight gain when the laxative is discontinued 6.
• The loss of electrolytes, particularly sodium and potassium, can lead to muscle weakness, fatigue, and other symptoms 4, 3.
• Severe electrolyte imbalances can lead to life-threatening complications, such as cardiac arrhythmias and respiratory failure 5.