A water retention laxative such as Miralax is the type of laxative most commonly recommended by pediatric healthcare providers for the treatment of encopresis. When Miralax is prescribed, parents are usually advised to give one or more "caps" or "half caps" of the powder diluted in water. A "cap" is the amount recommended on the container and is therefore assumed to be the "standard" dose. However, the fact is that there is no one dose that is the most efficacious for all children. A cap or half cap may be too much or too little as evidenced by its effect on stool consistency. In my book, The Ins and Outs of Poop, I strongly recommend dosing PEG laxatives like Miralax by the teaspoon (one cap is approximately 5 level teaspoons). Dosing by teaspoons makes it much easier to determine the most efficacious dose for each child.
Why is getting just the right dose so important?
The key to successfully treating encopresis is to find that dose of a laxative that enables a child to have 1 to 2 medium-to-large, very comfortable BMs a day, 5-7 days a week that are softer than the normal "toothpaste" consistency.
The desired consistency is like that of pudding or applesauce but not watery.
Over the many months required to effectively treat encopresis, the laxative dose may need to be raised or lowered in small increments to maintain the desired consistency until withholding has stopped and the rectum has shrunk back to it's normal size.