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Preparing for Colonoscopy

The goal of preparing for a colonoscopy is to have a completely clean colon so that small polyps and other abnormalities can be seen clearly. There are a number of preparation methods that rid the colon of feces, and a provider may have recommendations based on the patient's age, personal preferences, kidney function, and physical stamina.

  • The most common preparation for colonoscopy involves drinking a solution of polyethylene glycol which causes diarrhea to clear the colon of its contents. Polyethylene glycol comes in various fruit flavors, and patients have several hours to drink it. Typically, the patient will have clear liquids the day before the colonoscopy and take half of the polyethylene glycol solution that evening. The other half is taken about five hours before the colonoscopy the following day. Patients should drink a lot of fluids and continue to drink clear liquids up until two hours before their colonoscopy. A laxative pill may also be prescribed to help with the evacuation process.
  • Smaller volume solutions or pill preparations are alternatives to polyethylene glycol. They work much the same way, but the patient doesn't have to drink such large volumes of liquid.
  • A phosphate solution is another alternative. This preparation consists of two rounds of phosphate-rich liquid of 45 ml each the night before and day of the colonoscopy. Patients should drink at least two quarts of water to replace losses.
  • A phosphate tablet preparation of about 30 pills is also available and very effective for cleansing the colon. This preparation also requires the patient to drink at least two quarts of water.

Phosphate preparations should be avoided in patients with significant heart or kidney problems and in elderly patients who have difficulty maintaining hydration. Patients with significant liver problems should only use phosphate preparations with caution.