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Medications > All About Miralax

All About Miralax

Miralax-(1).pngWhat is Miralax?

Miralax is a stool softener. The active ingredient, polyethylene glycol (PEG), works by increasing the water content of the stool. 

The more PEG taken, the softer the stool. PEG is not a laxative and should not cause cramps. It is not habit forming. It is not absorbed into the body. It can be used as long as it is needed without concern. It is tasteless and dissolves easily in liquids. It may be dissolved in water, with a slight change to its taste, but is palatable. Be careful of adding it to drinks high in sugar (even juice), since your child will be on it for a long time, and they don't need the added sugar. Consider making flavored water with your child's favorite fruit. Simply put cut up fruit in water in the refrigerator for a couple hours. Infused water tastes great and is a healthy base for your Miralax mixture - or anytime your kids need a drink and don't like plain water.

How do I mix and measure PEG?

PEG comes as a white powder in a bottle with a measuring cup. The measuring cap has a line on the inside labeled “17 grams”.
  • Fill the cap to that line and mix with 1 cup (8 oz.) of liquid.
  • Any non-carbonated (not fizzy) drink is OK, but sugar free drinks may be less likely to cause gas and cramps. 
  • It takes about 5 minutes of occasional stirring to dissolve.
  • It is important to always mix PEG in this proportion: One capful (17g) to 8 oz. liquid. If you wish, you can mix more than 8 oz. at a time. For example, if you make 8 cups (2 quarts) of liquid with 8 capfuls of PEG. Keep this in the refrigerator and pour the dose from this supply.

How much should I give?

The chart below will help guide your dosing.

You may give the “3 Day Cleanout” dose if your child is impacted (as directed by your doctor) and then start the chronic constipation daily dose as a maintenance. Some people call this an "overnight" cleanout, but it usually takes several days of Miralax. Do not wake your child to give the Miralax.

Your child should have 2-3 milkshake consistency stools per day. If the stools are too hard or not frequent enough, increase the dose. If the stools are watery or too numerous, decrease the dose.

“Diarrhea” is common at the beginning of treatment because of stool leakage around an impacted stool. Once the solid stool mass that is impacted is passed, the "diarrhea" will stop. DO NOT stop the Miralax at this stage.  

You may change the dose in small increments every 3 days. The dose is changed by how many ounces of the liquid are given, not by how it is mixed. The average time to treat constipation is 8 months, with a range of 6-12 months, so don’t stop too prematurely, especially if potty training or family changes are occurring. Until kids eat healthy amounts of fruits, vegetables, and quality fiber foods; drink sufficient water; AND take the time to sit on the toilet regularly, they will need the Miralax.

Use the Bristol Stool scale below to keep track of what the stools look like. Ideal stools are type 4 in children (not infants). If the stools are 1 or 2, increase the Miralax. If they are 3, 4, or 5, keep it the same or lower the amount slightly. If they are 6-7, consider leakage around a large stool mass or diarrhea (see above). Altering the miralax dose will depend on the cause.

Body Weight (lbs)

Chronic Constipation

3 Day Cleanout

20 3 oz. daily 4 oz. twice daily
30 4 oz. daily 4 oz. twice daily
40 5 oz. daily 5 oz. twice daily
50 6 oz. daily 6 oz. three times daily
60 8 oz. daily 6 oz. three times daily
70+ 8 - 16 oz. daily  6 - 8 oz. three times daily

How long do we use Miralax?

Miralax should be used until a child can easily pass stools daily that are a 4 on the scale below. Most children need to be on the Miralax for 6-12 months. This seemingly long time allows the child to not only get in the habit of stooling on a regular basis, but also allows time for dietary changes to help keep stools soft without the aid of Miralax. See our Constipation page for good foods to eat to help with keeping the stools soft.

When a child is constipated, the gut stretches to hold extra stool. This gut muscle must get back into shape in order to stool properly. This can take quite a bit of time, just like getting any other muscle into shape. If the Miralax is stopped prematurely, the stools quickly back up again. 

Most kids need 6-12 months of regular Miralax use. This regular use generally starts 1-2 times/day, but can wean down to a few times per week if they eat enough high fiber foods, drink enough water, and take the time to sit on the toilet daily. 

3 Day Cleanout

We recommend the 3 Day Cleanout (sometimes called "overnight cleanout") to help empty out the large amount of stool that has built up over time. It is important to continue a maintenance dose of Miralax daily for many months. The 3 Day Cleanout sometimes needs to be repeated every 2 weeks despite daily Miralax.

Some people call this an "overnight" cleanout, but it usually takes several days of Miralax. Do not wake your child to give the Miralax. 

During the 3 Day Cleanout your child will take the Miralax amount as suggested by the weight chart above.

You may also want to give a laxative during this time. Miralax keeps water in the gut, which softens the stool. It is not a stimulant laxative. Stimulant laxatives help squeeze the gut to push stool out. Safe stimulant laxatives include Senna or bisacodyl. Both are available over the counter or as a prescription. The stimulant laxatives should only be given for 1-3 days, never long term. 

  • Senna is available as a 15mg chocolate chew or as a 8.6mg tablet over the counter and in liquid form by prescription. It is given at bedtime to work overnight. Dose by your child's weight:
    • 22-55 pounds: 2.5ml (prescription) or 1/2 tablet (OTC pill)
    • 55-88 pounds: 5 ml (prescription), 1 tablet, or 1/2 chocolate chew
    • 88+ pounds: 10 ml (prescription), 2 tablets or 1 chocolate chew
  • Bisacodyl is available as a 5mg tablet and is also given at bedtime. 
    • 23-88 pounds: 1 tablet
    • 88+ pounds: 1-2 tablets

Expect watery stools initially. This is because the Miralax keeps liquid in the gut, which in the end will soften the stool, but when there's a large stool mass it leaks around it and comes out still liquid. Once the large stool that has been in the gut too long finally comes out, the liquid won't have to leak around any more. It can take up to two weeks to finally be normal stool consistency, but if your child hasn't had a large stool mass at least once during the 3 day clean out, please talk to one of our staff. 

Don't forget to use Miralax daily even once the stools are soft. You can wean back on the amount, but still give it regularly to keep the stools looking like a #4 in the chart below. You can repeat the 3 Day Cleanout every 2 weeks as needed.

If the 3 Day Cleanout doesn't work, schedule a visit with your pediatrician. An exam will be needed, and depending on findings, further studies may be indicated.

Miralax Safety

 Please visit Dr. Stuppy's blog on Miralax safety. 


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