What is the recommended dosage of Miralax (polyethylene glycol) for treating constipation?

Miralax (Polyethylene Glycol) Prescription for Constipation

The recommended dosage of Miralax (polyethylene glycol 3350) for treating constipation is 17 grams once daily, mixed in 4-8 ounces of beverage, with dosing adjusted based on symptom response. 1, 2

Standard Dosing Regimen

• Initial dose: 17 grams once daily 1
• Administration: Dissolve powder completely in 4-8 ounces of any beverage (cold, hot, or room temperature) 3
• Timing: Preferably taken in the morning, though timing is not strictly defined 2
• Duration:
  • FDA-approved for up to 7 days without medical supervision 3
  • Can be used safely for up to 6 months under medical supervision 2, 4
  • Long-term use up to 12 months has been shown to be safe in clinical studies 5

Dose Titration

• Adjust dose based on symptom response and side effects 1, 2
• No established maximum dose in guidelines 1
• For severe constipation requiring rapid relief within 24 hours, higher doses (68g) have been studied but should only be used under medical supervision 6

Efficacy Expectations

• Efficacy typically seen in week 2 of treatment 2, 6
• Success rate of 78.3% for medication-induced constipation vs. 39.1% for placebo 7
• 52% of patients achieve treatment success with regular use vs. 11% with placebo over 6 months 4

Monitoring Parameters

• Frequency and consistency of bowel movements
• Relief of constipation symptoms
• Side effects (primarily gastrointestinal)
• No significant changes in laboratory values (electrolytes, renal function) have been observed in studies up to 6 months 4, 5

Common Side Effects

• Abdominal distension
• Soft stools
• Flatulence
• Nausea
• Bloating and abdominal discomfort 1, 2

Important Precautions

• Ensure adequate hydration during treatment 1, 2
• Do not combine with starch-based thickeners used for difficult swallowing 3
• Ensure powder is fully dissolved before drinking 3
• Do not use in patients with suspected bowel obstruction 2
• For patients 16 years of age or under, consult a doctor 3

Clinical Pearls

• PEG 3350 works as an osmotic laxative and has been shown to be effective for both acute and chronic constipation 1, 4
• Response to PEG has been shown to be durable over 6 months without evidence of tachyphylaxis 1, 5
• Constipation often returns after discontinuation, with 61.7% of patients requiring additional treatment within 30 days after stopping 2
• Monthly cost ranges from $10-$45, making it a cost-effective option 1
• PEG 3350 should not be used for bowel preparation before colonoscopy, as FDA-approved bowel preparation products are more effective 8