Miralax (Polyethylene Glycol 3350) Dosing and Administration Instructions
The standard adult dose of Miralax is 17 grams (one capful or one packet) dissolved in 8 ounces (approximately 240 mL) of any beverage, taken once daily. 1, 2
Standard Adult Dosing
- Initial dose: 17 g once daily 1
- Preparation: Mix the powder in 8 ounces of liquid (water, juice, coffee, tea, or any beverage) 1
- Timing: Can be taken at any time of day
- Duration: FDA-approved for occasional constipation, but evidence supports safe and effective use for up to 6 months in chronic constipation 1
Dose Titration
Adjust the dose based on symptom response and side effects, with no clear maximum dose. 1 The powder is unflavored and grit-free, making it easy to dissolve in any beverage 2.
- If inadequate response after several days, the dose can be increased
- If diarrhea or excessive loose stools occur, reduce the dose
- Most patients respond well to the standard 17 g daily dose 1
Pediatric Dosing Considerations
For children, dosing differs significantly from adults:
- Mean effective dose in children: Approximately 0.8-0.84 g/kg/day 3
- Range: 0.27-1.42 g/kg/day, adjusted to achieve 2 soft stools per day 3
- Measurement: A leveled teaspoon contains approximately 3.3 grams; a leveled tablespoon contains approximately 10 grams 4
Important Clinical Considerations
Common side effects include bloating, abdominal discomfort, cramping, flatulence, and diarrhea 1, though these are typically mild to moderate and often decrease after the first week of treatment 5.
Key Points:
- Efficacy is durable: Response has been demonstrated to be sustained over 6 months of continuous use 1
- No serious safety concerns: Studies show no significant differences in serious adverse events compared to placebo 1
- Cost-effective: Monthly cost ranges from $10-45, making it one of the most affordable laxative options 1
- Widely available: Over-the-counter without prescription 1
Clinical Algorithm for Use:
- Start with 17 g once daily mixed in 8 oz of any beverage
- Assess response after 3-7 days
- If inadequate response: increase dose gradually
- If diarrhea occurs: reduce dose
- Continue treatment as needed—safe for extended use up to 6 months based on evidence 1
The 2023 AGA-ACG guidelines position PEG early in the treatment algorithm for chronic constipation, either after a trial of fiber supplementation or in combination with fiber 1, reflecting its favorable efficacy, safety profile, and cost-effectiveness compared to other laxative options.