How to Do a Bowel Prep for Colonoscopy or Surgery

Bowel preparation, also known as bowel prep, is the process of removing feces (stool) from your colon before a medical or surgical procedure such as colonoscopy or colorectal surgery. Removing feces and other residues reduces the risk of intestinal abrasion and makes it easier to view the colon through a colonoscope.

If bowel prep is needed, your healthcare provider will provide you with detailed instructions that you will need to follow exactly. This would involve short-term changes in diet and medications followed by a schedule of different laxatives that help clear the bowel.

The article explains the steps involved in bowel preparation, including possible side effects and tips to make the process easier.

1

Medication Changes (7 Days Prior)

Man talking to his doctor
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Bowel prep procedures generally start with the temporary adjustment of certain medications. Chief among these are anticoagulants (a.k.a. "blood thinners") that need to be stopped seven days in advance. This prevents excess bleeding in the event of an injury or a procedure like a polyp removal.

These include blood thinners like:

  • Coumadin (warfarin)
  • Plavix (clopidogrel)
  • Lovenox (enoxaparin)

Other drugs may need to be stopped or reduced one to five days before the procedure, including:

  • Antidiarrheals like Imodium (loperamide), Lomotil (atropine/diphenoxylate), and Pepto Bismol (bismuth subsalicylate), which slow intestinal motility
  • Nonsteroidal anti-inflammatory drugs (NSAIDs) like aspirin, Advil (ibuprofen), and Aleve or Motrin (naproxen), which can increase the risk of bleeding
  • Fiber supplements like Metamucil, Citrucel, and Benefiber, which cause the bulking of stools
  • Iron supplements, which can cause grayish staining of the intestinal walls and should not be taken a day before the procedure
  • Certain diabetic medications, which may require a dose reduction a day before the procedure and complete stoppage on the morning of the procedure
2

Dietary Change (3 Days Prior)

Three days before the procedure, you will be asked to avoid high-fiber foods that are hard to digest and remove from the colon during bowel prep.

Opt instead for foods that are easier to digest and produce minimal residue. These are foods made with refined wheat that pass through the digestive tract relatively easily.

Foods to Avoid
  • Red meat

  • Raw vegetables

  • Corn, peas, or apple skins

  • Whole grain bread

  • Deep fried foods

  • Nuts and seeds (or products that contain them)

  • Popcorn

  • Dried fruits

  • Dried beans

  • Whole grain cereals

Foods to Eat
  • Cream soups

  • Smoothies

  • Eggs

  • Mashed potatoes

  • Baked, broiled, or steamed fish

  • Skinless chicken 

  • Steamed, peeled vegetables

  • Regular pasta 

  • White rice

  • White bread

  • Pudding

3

Dietary Changes (1 Day Prior)

One day before your procedure, your healthcare provider will place you on a clear liquid diet. A liquid is considered clear if you can see through it. For example, apple juice would be considered acceptable, while orange juice or milk would not.

Acceptable fluids on a clear fluid diet include:

  • Lemon-lime soda
  • Ginger ale
  • Club soda
  • Apple juice
  • White grape juice
  • Clear chicken or beef broth
  • Black coffee (without milk, cream, or creamer)
  • Black tea or herbal tea (without milk, cream, or creamer)
  • Lemon or lime gelatin
  • Lemon or lime popsicles
  • Lemon, lime, or colorless sports drinks
  • Water

Avoid Red, Orange, and Purple

Do not drink anything that's red, orange, or purple on a clear fluid diet. These food dye colors can stain the walls of the colon and make it harder to see bleeding. Yellow, green, or blue drinks are generally OK.

You would also need to avoid alcohol, including beer and wine, the day before your procedure. This is because alcohol is dehydrating and you will already lose a lot of water during bowel preparation.

4

Bowel Prep Timeline (1 Day Prior)

One day before your procedure, you would begin the actual bowel preparation, which involves laxatives and other medications you need to take on a prescribed schedule.

The timelines and procedures can vary, but here is an example commonly used for a colonoscopy bowel prep:

  1. Upon waking, eat or drink nothing but clear liquids.
  2. At noon, take the prescribed dose of stimulant laxative, like Dulcolax (bisacodyl), with a full glass of water. This type of laxative increases the contraction of the intestinal muscle, moving stools faster through the digestive tract.
  3. At 5:00 p.m., you will mix an osmotic laxative like MiraLAX (polyethylene glycol) with 1 gallon of water. This type of laxative draws water out of the walls of the colon, effectively flushing it out.
  4. At 6:00 p.m., drink 8 ounces of the MiraLAX solution every 10 to 15 minutes until two-thirds is consumed. Save the rest in the refrigerator for the following morning.
  5. At 9:00 p.m., chew two simethicone tablets. Simethicone is an antifoaming agent that helps decrease gas and bloating.
  6. At 10:00 p.m., take two more simethicone tablets.

Depending on your sensitivity to the laxative, you may start experiencing clearance around midday. The major clean-out may occur after taking the MiraLAX solution, so stay close to the toilet. Make sure to drink plenty of water or a sports drink with electrolytes to avoid dehydration.

You may also need to get up in the middle of the night to use the toilet, so keep a nightlight on in the bathroom to avoid accidents.

Important Note

This step-by-step guide is only intended as an example of a bowel prep procedure. Always follow your healthcare provider's instructions.

5

On the Morning of Your Procedure

Upon waking, finish all of the remaining MiraLAX solution, drinking 8 ounces every 10 to 15 minutes. You should finish no later this three hours before the scheduled procedure.

Thereafter, you should take nothing by mouth. If there are chronic medications you need to take, do so with small sips of water right after you wake up.

Some people do a light enema in the morning to ensure that there is no remaining residue in the bowel. However, if you did the bowel prep correctly, this is usually not necessary.

If you do decide to use an enema, do so lightly. Not only does overfilling the colon risk a messy accident on the way to your procedure, but it also places stress on the tissues of the rectum and colon, causing discomfort and swelling.

6

Side Effects and Risks

Generally speaking, bowel prep is safe and poses little risk to your health. Common symptoms include:

  • Rectal pain
  • Abdominal cramping
  • An uncomfortable feeling of fullness
  • Bowel leakage
  • Nausea or vomiting
  • Sudden cold sweat

In very rare instances, the polyethylene glycol in MiraLAX can cause acute kidney failure. This generally affects people with pre-existing kidney disease, but some cases have been noted in people with no known history of kidney problems.

Other serious symptoms can occur if you lose more water than you replenish. This can lead to severe dehydration, the symptoms of which include:

  • Decreased urine output
  • Dizziness or lightheadedness
  • Rapid heartbeat or palpitations
  • Rapid breathing
  • Fatigue and weakness
  • Shortness of breath
  • Confusion
  • Fainting

Checking for Dehydration

The best way to monitor for dehydration is to look at the color of your urine. Dark urine indicates that you need more fluid, while light yellow or colorless urine indicates adequate hydration.

7

Helpful Tips

Bowel prep can be unpleasant, but there are things you can do to minimize the discomfort and reduce potential risks.

Here are some tips that can help:

  • You can make the MiraLAX solution more palatable by mixing it with a powdered drink like lemon Crystal Light. However, avoid red, orange, or purple Crystal Light.
  • Refrigerating the MiraLAX solution helps reduce some of the off-putting taste as well.
  • Purchase extra-soft, unscented toilet paper or disposable baby wipes to minimize rectal swelling and soreness.
  • After wiping, apply a barrier ointment, like those used for diaper rash, to keep the anal tissues soft and moisturized.
  • To avoid bathroom accidents, wear loose-fitting clothes that can be easily removed, like pajama bottoms or boxer shorts.
  • If you are feeling lightheaded during bowel prep, slow down the intake of MiraLAX. Avoid straining when going to the bathroom as this can also cause lightheadedness.
  • If you have diabetes, pay extra attention to your blood sugar levels. Have liquid glucose or a sweetened drink light Sprite on hand if your sugar levels drop due to hydration.

If you followed the instructions but still find dark fluid or traces of poop coming out, call your healthcare provider for advice. If your bowel is not entirely clear by the time of your appointment, you may need to reschedule.

Summary

Bowel preparation is used to clear feces and other residues from the colon prior to colonoscopy or other colorectal procedures. It requires you to temporarily stop certain medications and adjust your diet one to seven days before the bowel prep.

Bowel prep often involves the combination of a stimulant land osmotic laxative to clear the intestine, accompanied by simethicone tablets to reduce bloating and cramps. On the day of bowel prep, you need to drink plenty of water or a sports drink to avoid dehydration.

9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Jennifer Whitlock, RN, MSN, FN
Jennifer Whitlock, RN, MSN, FNP-C, is a board-certified family nurse practitioner. She has experience in primary care and hospital medicine.