Oral bowel cleansing agents (Guidelines)

TAM (Treatments and Medicines) NHS Highland
NHS Highland

Objectives

This guideline provides safe and evidence‑based recommendations for prescribing and administering oral bowel cleansing agents prior to colonoscopy.

It summarises key safety principles derived from ESGE guidance and the National Patient Safety Agency safety alert RRR012.

Audience

  • All NHS Highland
  • Primary and secondary care
  • Adults only: Applies to all adult patients undergoing colonoscopy requiring oral bowel preparation.

Applies to:

  • Medical staff
  • Independent nurse prescribers
  • Endoscopy nurses
  • Endoscopy administrative staff involved in patient preparation
  • Referring clinicians in primary and secondary care

Bowel preparation prescribing flowchart

The following flowchart provides a simplified decision pathway for prescribing bowel preparation.

Responsibilities

Prescribers:

All bowel cleansing preparations must be prescribed by a suitably trained medical prescriber or independent nurse prescriber following clinical assessment.

Referring Clinicians:

  • Ensure renal function checked within 3 months
  • Provide past medical history, medications and allergies
  • Identify frailty
  • Review medications that may need temporary discontinuation

Endoscopy Team:

  • Vet referrals
  • Provide patient instructions
  • Identify high‑risk patients

First line bowel preparation

FIRST LINE oral bowel cleansing agent: Plenvu (PEG-based preparation).

  • PEG-based preparations are preferred due to lower risk of electrolyte imbalance and fluid shifts.

Dosing regimen: Split dose regimen:

  • Dose 1: Evening before procedure
    • One Dose 1 sachet dissolved in 500 mL water
    • Drink over 30 minutes
    • Follow with 500 mL clear fluids
  • Dose 2: Morning of procedure
    • Dose 2 sachets A and B dissolved in 500 mL water
    • Drink over 30 minutes
    • Follow with 500 mL clear fluids
    • Second dose should be completed at least 2 hours BEFORE procedure.

Dietary preparation

Low fibre diet the day before colonoscopy.

Foods allowed:

  • White bread
  • Rice and pasta
  • White fish or chicken
  • Plain yoghurt
  • Cheese
  • Butter or margarine
  • Clear jelly (not red or purple)

Foods to avoid:

  • Red meat
  • Pink fish
  • Fruit and vegetables
  • Brown rice
  • Wholemeal bread or pasta
  • Seeds and nuts
NO solid food after 13:30 the day before procedure.

Contraindications

  • GI obstruction or perforation
  • Ileus or gastric retention
  • Acute GI ulceration
  • Severe IBD or toxic megacolon
  • Reduced consciousness or aspiration risk
  • Allergy to ingredients
  • Unsafe swallow
  • Ileostomy

Complications

  • Hypovolaemia
  • Hypokalaemia
  • Hyponatraemia
  • Nausea or vomiting

Patients unable to tolerate preparation should contact the Endoscopy Department.

Special Patient Groups

  • Diabetes: Diet controlled: Follow standard instructions
  • Diabetes: Medication or insulin treated:
    • Prefer morning procedure
    • Monitor blood glucose
    • Treat hypoglycaemia with glucose tablets or sugary drink.
  • Renal impairment: PEG preparations first line.
  • Haemodialysis: Discuss with renal team.
  • Peritoneal dialysis: Continue dialysis with dialysate removed before procedure.
  • Renal transplant: Use PEG preparations and avoid sodium phosphate.

Frail / high-risk patients: inpatient management

Consider inpatient bowel preparation for frail or high‑risk patients.

Frailty should be assessed using the Clinical Frailty Scale (CFS)

Patients with CFS ≥5: should be considered frail and may require modified preparation or inpatient management.

1 to 3

 Fit / well

4

 Vulnerable

5 

 Mild frailty

6

 Moderate frailty
7 to 9  

Severe frailty / terminally ill

On admission:

  • Check renal function, magnesium and phosphate
  • Review medications
  • Provide low residue diet and oral fluids

Renal function should be rechecked on day of procedure.

Patient education

Patients should be advised to watch the NHS bowel preparation video and follow the written instructions carefully.

Improving tolerance

  • Chill preparation before drinking
  • Use a straw
  • Add lemon or lime cordial
  • Chew sugar‑free gum

Monitoring and audit

Compliance monitored through endoscopy quality assurance, review of adverse events, and periodic audit of prescribing practice.

Abbreviations

  • CFS: clinical frailty scale
  • CKD: chronic kidney disease
  • GI: gastrointestinal
  • IBD: irritable bowel disease
  • PEG: percutaneous endoscopic gastrostomy

Editorial Information

Last reviewed: 30/04/2026

Next review date: 30/04/2029

Author(s): Gastroenterology.

Version: 2

Approved By: TAM Subgroup of the ADTC

Reviewer name(s): Mr A Grant, Consultant General Surgeon.

Document Id: TAM482

References
  • ESGE Bowel Preparation Guideline (2019)
  • British Society of Gastroenterology endorsed guidance
  • National Patient Safety Agency Safety Alert RRR012 (2009)