This information was developed by the Publications Committee of the American Society for Gastrointestinal Endoscopy (ASGE). For more information about ASGE, visit www.asge.org.
This information is intended only to provide general guidance. It does not provide definitive medical advice. It is important that you consult your doctor about your specific condition.
It is extremely important that your colon be thoroughly cleaned before your colonoscopy. This will let the doctor see any abnormalities, such as colon polyps, during the procedure. Polyps are small growths in the colon that could later turn into cancer. Cleansing the colon before a colonoscopy is called bowel preparation, or "prep." It involves taking medication that causes diarrhea, emptying the colon. The medication is taken by mouth, and comes in liquid or tablet form. You will also need to change what you eat during the day or two before the colonoscopy.
Your doctor will prescribe the type of bowel prep that is best for you. You will receive specific instructions. In general, here is what you can expect:
Tell your doctor what medications you're taking, especially aspirin products, arthritis medications, anticoagulants (blood thinners such as warfarin or heparin), clopidogrel, insulin or iron products. Most medications can be continued. Some can interfere with either the prep or the colonoscopy.
Your bowel must be clean so that your doctor can thoroughly examine your colon. Many patients feel that the bowel prep is the most difficult part of a colonoscopy. But it is important that you try your best to fully complete the prep.
Several types of bowel prep medications are available; the two medications used most often in bowel prep are described in the box on this page. Your physician may recommend one of these or other preps which are available. You will need to carefully follow your doctor's instructions about the exact dose and timing of your prep. Some types of prep may be covered by your medical insurance. You'll want to find out if you have any out-of-pocket costs.
Your medical condition is the most important factor in deciding which type of bowel prep is best for you. Tell your doctor if you are pregnant or breast feeding, or if you have a history of bowel obstruction. Let the doctor know if you have high blood pressure. Also, mention if you have any heart, kidney or liver disease, or if you have had any of these diseases in the past. You need to mention any allergies you have to medications to the doctor. If you have had difficulty with a bowel prep in the past, be sure to mention this as well. Other factors in choosing the type of prep are the time of the colonoscopy appointment, individual preferences (taste and amount of medication), and out-of-pocket costs.
Call your doctor and ask what to do if you are not able to complete the bowel prep as advised.
The type and severity of side effects differ among patients. They also vary with the product used. Some patients have nausea, vomiting, bloating (swelling in the abdomen) or abdominal pain. A prep can cause kidney failure, heart failure or seizures, but this is rare. Your doctor will explain the possible side effects of the prep selected for you.
Polyethylene glycol; Electrolytes oral solution (PEG-based products) may come as a powder to be mixed with water before use. They are available only by prescription and are taken by mouth. Although given in a greater volume than other products used in bowel prep, PEG-based products are often preferred for patients with kidney, heart and liver conditions. The reason is that they do not cause mineral or fluid changes that can lead to dehydration.
Sodium phosphate comes in tablet form to be taken by mouth and requires a prescription. In rare cases, sodium phosphate can cause kidney failure. Doctors consider this when deciding if sodium phosphate is appropriate for a given patient.