RE: Preferred Colon Prep for Colonoscopy in Dogs

dred.hall — Sun, 24 May 2026 12:06:30 GMT

This is what I wrote for the Improve endoscopy course notes. If you want to know how to stomach tube a conscious dog, you will have to do the course :-)

The patient should not be fed for at least 24 and preferably 36-48 hours before the procedure: water is always available. Faecal material is cleared by repeated enemas or by per oral lavage, with flushing during the procedure if necessary.

Lavage solutions are best for colonic preparation, particularly if ileoscopy is planned. Preferred preparations are iso-osmotic solutions of polyethylene glycol 3350 (PEG) mixed with electrolytes that produce osmotic diarrhoea that washes out the gut contents. Several commercial products (e.g. Colyte, GoLytely, Movicol, Plenvu) are available, although Kleanprep has been withdrawn. The patient is given 3 doses, each of 25‑30 ml/kg, at least two hours apart and, ideally, the last dose is given approximately 12 hours before colonoscopy. The patient should also receive at least one warm-water enema two hours before colonoscopy (or after anaesthesia induction). Any residual faecal material has to be washed out during the procedure. A peristaltic flushing pump attached to the colonoscope makes this much easier; there are adapters that fit to the instrument channel, allowing flushing via the biopsy channel.

A minority of dogs will voluntarily drink PEG3350 if it is dissolved in the water used to boil chicken. However, without flavouring, it has an unpleasant taste, and as large volumes must be given to dogs, a stomach tube is often needed for administration. A large-bore, thick-walled stomach tube (e.g. foal stomach tube, ideally red rubber) should be used for gavage in dogs. If necessary, the tube can be passed through a basket muzzle. Particular care should be taken in patients with dysphagia, laryngeal paralysis or delayed gastric emptying as inhalation of PEG3350 is potentially fatal. The process is repeated twice more at 2‑4 hour intervals the day before the procedure. Delivery via a naso-gastric tube is used in cats as they will not tolerate stomach tubing whilst conscious, but risks accidental instillation into the airways, so care must be taken when using this route.

Solutions of magnesium citrate or sulphate can also be used as osmotic cathartics at a single dose of 25 ml/kg. However, they can cause vomiting, abdominal discomfort and dehydration, and sometimes hypermagnesaemia. Low‑volume sodium phosphate solutions may be more tolerable, but studies in dogs have shown that low‑volume sodium phosphate solutions produce poorer cleansing than PEG solutions. Oral sodium phosphate tablets (Osmoprep) have been withdrawn as
>20 tablets had to be swallowed. A recent paper in the Vet Record <DOI: 10.1002/vetr5432> described adequate cleansing using a mixture of sodium picosulphate and magnesium citrate, but I am not aware of it being available commercially.

Enemas are a cheaper and sometimes easier solution, but multiple, large-volume, high enemas are required, and the quality of colonic cleansing is often poor. This is especially true in larger patients, and if ileoscopy is planned. The method is unpleasant for patients and staff, and lavage is also more suitable than multiple enemas if there is severe anorectal pain. In medium-sized dogs, at least one litre of warm water per 30 kg should be used for each enema. The enema tube is well lubricated and gently inserted to the level of the last rib. Warm water is instilled either by gravity from an enema bucket rather than a Higginson pump. During instillation, the tube is moved back and forth to loosen the faeces. Liquid may escape from the anus during the procedure when the colon is full: more fluid should not be forced in, especially if the patient vomits. Enemas are repeated until the liquid runs clear, containing no particulate matter.

Irritant laxative enemas (e.g. soap) should not be used as they may cause artefactual inflammatory changes in mucosal biopsies, although in the USA bisacodyl enemas are used. Finally, of course, phosphate enemas should never be used in cats and small dogs as they can cause fatal hyperphosphataemia.

RE: Preferred Colon Prep for Colonoscopy in Dogs

Dinu Catilina — Tue, 19 May 2026 08:26:22 GMT

I don't do many but my approach is nothing solid for 48 hours prior. The issue is owner compliance, it is not uncommon to find food, grass, (dog nails once!), etc in the stomach and I suspect it is the same situation when we find faeces in the colon. Enema helps but there is always a bit of residual water and we end rotating the dogs quite a bit until we get to the ileo-colic junction. You can always aspirate it through the scope but I hate doing it, makes me feel like I will never clean that scope well again.