01Principles and purposeThe professional or clinical skill and the decisions it supports.
Bowel-cleansing agents create deliberate diarrhoea to expose the colonic mucosa. The same effect can cause dehydration, acute kidney injury and electrolyte disturbance, particularly in frail people with poor intake, renal impairment, heart failure or medicines that alter renal perfusion.
The prescription must name the product, mixing volume, additional clear fluids, timing and medicine plan. Mechanical obstruction, ileus, perforation, toxic megacolon and severe acute inflammatory bowel disease are contraindication patterns requiring clinical reassessment rather than escalation of the purgative.
Key points
- Exclude obstruction, ileus, perforation, toxic megacolon and severe acute colitis before bowel cleansing.
- Assess hydration, renal function, electrolytes, frailty, swallowing and heart failure risk before prescribing.
- Review diuretics, renin-angiotensin blockers, NSAIDs, lithium, diabetes medicines and antithrombotics individually.
- Use the exact licensed product mixing, clear-fluid and timing instructions; brands are not interchangeable.
- Align the final dose with endoscopy and any anaesthetic fasting plan while preserving permitted hydration.
- Stop and seek review for severe pain, progressive distension, persistent vomiting, absent stool output or collapse.
02Situations and prioritiesThe context, relevant information and actions that matter most.
Frailty, reduced intake, renal impairment, heart failure, cirrhosis and baseline electrolyte disturbance increase the risk of dehydration and biochemical harm.
Diuretics, renin-angiotensin system blockers, non-steroidal anti-inflammatory drugs, lithium and medicines with narrow therapeutic windows require an explicit peri-preparation plan.
Preparation choice and timing depend on the procedure, product licence and anaesthetic fasting plan; instructions cannot be transferred casually between brands.
Split dosing commonly improves cleansing and tolerability, but completion time must fit the endoscopy unit and sedation or anaesthetic requirements.
Patients need plain instructions about allowed clear fluids, expected diarrhoea, access to a toilet and symptoms that should stop dosing and prompt contact.
03Assessment and interpretationHow to gather information, assess the situation and recognise uncertainty.
Consider the information, its meaning and its limitations before deciding what follows.
- 01
Clinical contraindication screen - Why
- exclude obstruction, perforation, ileus, toxic megacolon and severe acute inflammatory disease
- Interpretation and limitations
- Symptoms and recent imaging should be reviewed before prescribing; proceeding despite a suspected mechanical problem can worsen distension or perforation.
- 02
Renal function and electrolytes - Why
- identify patients at risk of acute kidney injury, sodium or potassium disturbance
- Interpretation and limitations
- The need and timing depend on age, comorbidity and product; abnormal results require correction or an alternative plan.
- 03
Medicine reconciliation - Why
- prevent accumulation, dehydration-related nephrotoxicity and loss of essential medicines during purging
- Interpretation and limitations
- Document which drugs are held, continued or retimed and when they restart, rather than giving a blanket instruction.
- 04
Hydration assessment - Why
- check oral intake, postural symptoms, weight change and clinical volume status
- Interpretation and limitations
- Clear-fluid intake can be inadequate despite apparent compliance, particularly in frail patients or those with swallowing difficulty.
- 05
Preparation-quality assessment at procedure - Why
- determine whether mucosal views are diagnostically adequate
- Interpretation and limitations
- Poor cleansing may require repeat preparation, an alternative regimen or another modality; it should not be hidden by a normal label.
04Worked approachesCases with ordered reasoning, an action and a check of the outcome.
01Worked case: applied bowel preparation safetyReach a specific decision and confirm it happenedA frail adult booked for morning colonoscopy takes furosemide for ankle oedema and ramipril for hypertension, has stage 3 chronic kidney disease, postural dizziness, sodium 132 mmol/L and creatinine increased from 120 to 168 micromol/L after poor intake.+
- 1Defer bowel preparation and colonoscopy because the patient is clinically volume depleted with acute kidney injury and hyponatraemia; arrange medical assessment and correction rather than issuing a kit.
- 2After rehydration, repeat observations, sodium and creatinine. Two days later dizziness has resolved, sodium is 137 mmol/L and creatinine has returned to 124 micromol/L.
- 3Confirm no obstruction, ileus, perforation, toxic megacolon or severe acute colitis, then prescribe the exact Moviprep A/B sachet two-litre course and at least one additional litre of permitted clear liquid.
- 4Omit ramipril and furosemide on the preparation day. Plan the ramipril review no earlier than 72 hours after the procedure; decide furosemide separately from volume status and its indication rather than giving both medicines one automatic restart time.
- 5At the 72-hour review the patient is eating and drinking, blood pressure is 132/76 mmHg, sodium 138 mmol/L and creatinine 122 micromol/L, so ramipril is restarted. The patient remains euvolaemic without congestion, so furosemide stays withheld pending the documented prescriber review.
02Licensed Moviprep split regimenTranslate the SmPC into executable instructionsA fit adult with normal renal function, no obstruction and a colonoscopy scheduled for 14:00 chooses Moviprep after medicine reconciliation.+
- 1At 19:00 on the evening before colonoscopy, dissolve one sachet A and one sachet B together to exactly one litre and drink this first Moviprep litre over the next one to two hours.
- 2At 09:00 on the procedure day, make the second A/B pair up to one litre and finish drinking it by 11:00; this starts the last dose within five hours and completes preparation at least two hours before the 14:00 colonoscopy.
- 3Drink at least one additional litre of permitted clear liquid across the course, stopping all clear fluid by 12:00 for this unit plan; if general anaesthesia is used, both Moviprep and clear fluids must finish at least two hours before the procedure.
- 4Stop solid food when treatment starts, allow travel time, and contact the unit for severe pain, vomiting, rectal bleeding or inability to complete the prescribed fluid.
- 5On arrival, verify both A/B litres, additional clear-fluid volume, stop times and stool clarity; inadequate cleansing requires a documented completion or repeat-examination plan.
03Obstruction warning pathwayStop purgative treatment and reassess acute symptomsAfter the first preparation glass, a patient develops colicky pain, increasing distension, repeated vomiting and passes neither stool nor flatus.+
- 1Stop Moviprep, keep nil by mouth, assess ABCDE and hydration and obtain urgent senior surgical review; do not give the second litre or add stimulant laxatives.
- 2Obtain renal function, electrolytes, lactate and urgent abdominal imaging to assess obstruction, ileus or perforation while resuscitating fluid losses.
- 3Verify transfer of care and document the suspected adverse event, product doses already taken and the revised plan for colonic investigation after recovery.
05Relevant medicines and safetySpecific regimens and precautions when the skill involves prescribing.
Moviprep powder for oral solution
For a 14:00 colonoscopy, make one sachet A plus one sachet B up to 1 litre at 19:00 the previous evening and drink over 1 to 2 hours; repeat at 09:00 and finish by 11:00. Take at least 1 additional litre of permitted clear liquid and stop it by 12:00 under this plan.Do not use with gastrointestinal obstruction or perforation, gastric-emptying disorder, ileus, toxic megacolon, phenylketonuria or G6PD deficiency. Correct dehydration first and assess hydration, renal and cardiac function, electrolytes and interacting medicines before prescribing. Stop the preparation and review sudden abdominal pain or rectal bleeding. For general anaesthesia, both Moviprep and other clear fluids must finish at least 2 hours before the procedure; follow any stricter anaesthetic instruction.
06Feedback, follow-up and evidenceReview outcomes, seek feedback and identify what to improve.
- Check whether the patient completed each dose and the recommended clear fluids, and record vomiting or inability to tolerate the regimen.
- Reassess renal function and electrolytes after preparation when baseline risk, symptoms or the product information indicates this is needed.
- After inadequate cleansing, identify the reason before simply repeating the same regimen because adherence, constipation or intolerance may require a different strategy.
- Ensure held medicines are restarted at the correct time and that diabetes control or anticoagulation is safely reassessed.
07Special situationsVariants, exceptions and circumstances that change the usual approach.
Prescription carries ownership
Bowel cleansing is active pharmacological treatment, so the prescriber remains responsible for contraindications, interactions and follow-up.
Brand instructions are not interchangeable
Macrogol and sodium-picosulfate products differ in volumes, electrolyte loads and licensed directions; use the exact current product information.
Clear fluids are part of the regimen
The additional permitted fluid reduces dehydration and cannot be omitted merely because the purgative solution volume was consumed.
Poor cleansing has consequences
An inadequately prepared colon increases missed-lesion risk and may expose the patient to another invasive procedure.
08Common pitfallsFrequent interpretation and management errors.
- 01
Giving oral bowel preparation before excluding obstruction or toxic megacolon can worsen a dangerous mechanical or inflammatory condition.
- 02
Copying yesterday's medicine list without addressing diuretics, nephrotoxic drugs or diabetes treatment overlooks predictable harm.
- 03
Using vague drink plenty advice instead of product-specific fluid instructions makes safe completion impossible to verify.
- 04
Repeating an inadequately tolerated preparation without changing the cause recreates the same risk and diagnostic failure.