The volume of liquid involved in a colonoscopy preparation, or “prep,” is a primary concern for patients because adequate cleansing of the colon is mandatory for a successful procedure. The goal of the prep is to flush out all solid matter so the physician can clearly view the colon lining to detect polyps or other abnormalities. Failure to consume the full prescribed amount of liquid often results in an incomplete prep, which can lead to a canceled or repeated procedure. The total fluid intake is a combination of the primary laxative solution and a substantial volume of additional clear liquids, with the exact number of ounces varying significantly depending on the specific product a physician prescribes.
Volume of the Primary Prep Solution
The most direct answer to how many ounces are in the prep solution itself depends on whether a high-volume or a low-volume product is used. Traditional, high-volume polyethylene glycol (PEG) solutions, such as GoLYTELY or Colyte, require the patient to consume a total volume of approximately 4 liters, which is equivalent to about 128 ounces of the mixed solution. This large volume is what physically flushes the colon clean, acting as a complete bowel washout.
Newer, low-volume preparations are designed to reduce the total liquid intake, often requiring the patient to drink between 2 and 3 liters of the primary solution, or roughly 64 to 96 ounces. These lower-volume options, like Suprep or Plenvu, are typically more concentrated and often contain additional laxative agents like sodium sulfate or ascorbic acid to maintain cleansing efficacy despite the smaller volume.
Regardless of the formulation, nearly all modern regimens utilize a split-dose approach, meaning the total volume of the laxative solution is divided into two separate portions. The first portion is consumed the evening before the procedure, and the second portion is consumed the morning of the procedure. This split-dose method is proven to be more effective at cleaning the entire colon, especially the upper right side, and is generally better tolerated by patients than a single large dose.
Total Clear Liquid Intake Requirements
The volume of the concentrated prep solution is only one part of the total liquid volume needed for a successful cleanse. Patients must also consume a substantial amount of additional clear liquids throughout the preparation period to ensure proper hydration and to support the laxative action of the medication. The osmotic nature of the prep draws fluid into the colon, making it necessary to replenish the body’s water stores to prevent dehydration, which is a major risk during the process.
For many low-volume preps, the instructions often mandate drinking two additional 16-ounce containers of water or clear liquid after each dose of the primary solution, adding another 64 ounces (2 quarts) to the total intake from the prep solution alone. Furthermore, patients are on a clear liquid diet for the entire day before the procedure, which involves drinking several liters of acceptable fluids throughout the day.
This supporting liquid volume is crucial because the laxative can only work effectively if there is enough fluid in the digestive system to push the waste through and out of the body. Studies have shown that patients who consume a higher volume of clear liquids in addition to the prep solution are more likely to have a completely clean colon. In total, a patient may consume well over 150 ounces of combined fluid across the day of preparation.
Acceptable Clear Liquids
Acceptable clear liquids include:
- Water
- Clear broth
- Apple juice
- White grape juice
- Sports drinks without red or purple dyes
- Plain gelatin
Scheduling the Liquid Consumption
The timeline for consuming the large volume of liquid is precisely structured and follows a split-dose protocol to maximize colon cleansing efficacy. The clear liquid diet begins the entire day before the procedure, and no solid food should be consumed after this point. The first dose of the primary prep solution is typically scheduled for the late afternoon or early evening the day before the colonoscopy.
Patients are generally instructed to consume the prep solution at a steady, measured pace, such as drinking 8 ounces of the liquid every 10 to 15 minutes. This pacing is important to prevent nausea and allow the body to process the high volume of fluid without overwhelming the stomach.
The second dose of the prep solution is consumed on the morning of the procedure. The timing of the second dose is the most time-sensitive part of the preparation, as it must be completed within a specific window relative to the procedure time. To allow for safe sedation, all liquid consumption must stop a few hours before the scheduled procedure, often four hours prior, though sips of water with medication may be permitted closer to the appointment. This strict schedule ensures the colon is actively cleansing right up until the procedure begins.
Tips for Successful Prep Intake
Consuming a large volume of liquid in a short timeframe can be a physical challenge, but several strategies can make the process more manageable. Chilling the prep solution significantly improves its palatability, as many people find the taste less objectionable when it is cold. Using a straw can also help bypass some of the taste buds at the front of the tongue, making it easier to drink the required amount.
To mask the salty flavor of some solutions, patients may add flavor packets, but it is important to use only light-colored options like lemon, lime, or orange, avoiding any red, purple, or blue dyes. If nausea begins during consumption, taking a short break of 20 to 30 minutes can help the stomach settle before continuing with the prep. Sucking on ginger candy or drinking ginger tea, if approved by a physician, can also help mitigate feelings of queasiness.