Your surgeon has given you a date for colorectal surgery. Your bowel must be empty before the surgery can take place so we are asking you take a bowel preparation (Klean Prep), at home. This page gives you instructions about how and when to start taking your Klean Prep.

Why do I need to take a bowel preparation?

Klean Prep is a drink that cleanses the bowel by increasing the water content of your stools. This will help flush everything out of your bowel so that it is empty ready for the surgery. It is important to take all of the bowel preparation.

If you are unable to take all of the preparation please let the admission staff know when you arrive for your surgery appointment.

Before taking Klean Prep

Please read the leaflet enclosed in the Klean Prep packaging as you should be aware of any possible side effects.

If you have allergies (hypersensitive) to any of the active substances or any of the ingredients of Klean Prep (or PKU - Phenylketonuria), please do not take the preparation and notify your Colorectal Specialist Nurse (the contact details are at the end of this leaflet).

At your pre-assessment appointment you may have been asked to stop some of your medication. If you are due to take any other medication, please take at least 1 to 2 hours before or at least an hour after the Klean Prep has finished working. Medications taken while the Klean Prep is working will be flushed through your digestive system and may not work as well.

If you have diabetes, please inform your Colorectal Specialist Nurse before taking Klean Prep at home.

If you are working, you will need to take the day before your surgery off. The Klean Prep will increase the frequency of your bowel movements.

If you are taking any of the following medications please contact your Colorectal Specialist Nurse for advice about if or when to stop taking:

  • Imodium (loperamide)
  • Codeine Phosphate
  • Lomotil (co-phenotrope)
  • Iron tablets (ferrous sulfate, ferrous fumarate)
  • Laxatives

2 days before your surgery

A low fibre diet in advised as food with lower fibre content passes easily through your bowels ensuring the bowel preparation works effectively. This will also limit the amount of undigested food that has to pass through your system. Listed below and on the next page are foods which are low in fibre.

  • Eggs - boiled or poached
  • White fish
  • Chicken
  • Lean meat for example beef, lamb, veal or ham
  • Gravy using stock cubes (white flour or cornflour to thicken)
  • White bread or rolls (avoid bread that has seeds)
  • Potatoes - boiled or mashed (remove skins)
  • White pasta/noodles
  • White rice
  • Butter/margarine - use sparingly
  • Jelly (avoid red coloured jelly)
  • Sugar/honey/treacle/fruit jelly/jams/marmalades (without peel)
  • Boiled sweets or clear mints
  • Drinks with no bits
  • Quorn, tofu textured vegetable protein

Please avoid fried food, seeds and grains especially sweetcorn and drink plenty of fluid.

Day before your operation

Breakfast 8:00am Have a good low fibre, non fried breakfast, taken from the list of foods above and on the previous page.

Please do not have any solid food after breakfast.

At 12:00 midday dissolve 1 sachet of Klean Prep into 1 litre (1¾ pints) of water and drink over one hour.

At 1:30pm dissolve 1 sachet of Klean Prep into 1 litre (1¾ pints) of water and drink over one hour.

At 3:00pm dissolve 1 sachet of Klean Prep into 1 litre (1¾ pints) of water and drink over one hour.

At 4:30pm dissolve 1 sachet of Klean Prep into 1 litre (1¾ pints) of water and drink over one hour.

At 6:00pm please take any Nutricia Pre-Op® drinks if you have been requested to.

Do not have any solid food after breakfast.

You should drink plenty of clear fluids (drinks without milk and bits in) such as squashes, clear juices, and tea/coffee without milk. The medication instructions advise that ‘The fluid content of the Klean Prep when reconstituted with water does not replace regular fluid intake and adequate fluid intake must be maintained’.

Klean Prep may be flavoured with clear juices and squashes such as lime cordial. It can be made in advance and chilled in the fridge. It is important that you do not dehydrate so please drink clear fluids between each sachet until midnight.

Morning of your operation

After midnight only drink water.

At 6:00am take any Nutricia PreOp® drinks you have been requested to.

At 7:00am do not eat or drink after this time.

What can I expect when the Klean Prep is working?

Klean Prep begins to work within 1 to 2 hours of starting the preparation. You will open your bowels frequently and eventually your motions should change from soft to loose and then watery.

Please make sure that you have access to a toilet all day until the effects have worn off.

What are the side effects of Klean Prep?

You may experience some of the following side effects:

  • Nausea
  • Vomiting
  • Bloating/fullness
  • It is normal in some people to experience some abdominal cramps
  • If you experience any soreness on the skin around your bottom, a barrier cream from your local pharmacy can be applied to the skin to protect the area. This is only temporary.

Please read the information leaflet in the packet, which advises that if you vomit, have abdominal distention (your stomach feels bloated or is visually bigger) or you experience stomach pain, then the solution should be taken over a longer period of time or stopped for a short time while any vomiting or abdominal pain gets better.

Who should I contact if I have any concerns?

If you experience a rash, swelling, severe vomiting then you may be having an allergic reaction. Please stop taking the preparation and contact the Colorectal Specialist Nurses. If you are having a severe reaction which results in you having difficulty breathing then call 999 immediately.

If you have any questions before you start to take this bowel preparation, please contact the Colorectal Specialist Nurses.

Contact information

Colorectal Specialist Nurses
Tel: 0300 422 5617
If your call is not answered, please leave a message and a member of staff will get back you within 24 hours.

Printable version of this page

How to take Klean Prep at home before your colorectal surgery GHPI1729_05_22 Department: Colorectal Review due: May 2025 PDF, 166.8 KB, 5 pages
Reference number GHPI1729_05_22
Department Colorectal
Review due May 2025