UK Clinical Pharmacy Association



This drug record does not cover the use of osmotic laxatives for bowel cleansing in preparation for procedures that require a clean bowel.

Issues for surgery

For prevention of hepatic encephalopathy – risk of impaired consciousness and encephalopathy if omitted.

For constipation – risk of constipation if omitted for prolonged period, which may further be exacerbated by medication administered perioperatively, e.g. opioids.

Advice in the perioperative period

Elective surgery 

Continue if required.


  • for patients having bowel cleansing agents prior to surgery – also see Bowel cleansing agents drug records.

Emergency surgery 

Continue if required.


  • for patients with suspected bowel obstruction/perforation
  • for patients who are unable to tolerate the volume of fluid required for safe administration.

Post-operative advice

Resume post-operatively, if needed, once enteral intake resumed.

Due to the volume of water required to reconstitute macrogol laxatives and the recommendation to drink around 1.5–2 litres of fluid with lactulose, review if the patient is nil by mouth or under a fluid restriction in the post-operative period.

If concomitant use of opioids or other medication that may cause constipation, or antibiotics that may cause diarrhoea, monitor response to treatment and adjust dose accordingly.

Review if patient develops reduced gastrointestinal motility (e.g. ileus) post-operatively.

Patients undergoing colorectal surgery

Review the need for osmotic laxatives post-operatively.

Patients undergoing head and neck surgery

For patients undergoing head and neck surgery who have dysphagia post-operatively and require macrogol laxatives, care should be taken to ensure doses are administered appropriately if there is a need to use thickening agents to support swallowing – see Further information.

Interactions with common anaesthetic agents


Interactions with other common medicines used in the perioperative period

The absorption of other medicinal products could be reduced due to an increase in gastrointestinal transit rate induced by macrogol laxatives. There have been isolated reports of decreased efficacy with some concomitantly administered medicines. Hence, other medicines should not be taken orally for one hour before and one hour after taking macrogol laxatives.


Lactulose may potentiate potassium loss induced by other medicines such as corticosteroids. This is unlikely to be an issue where corticosteroids are used as single doses to reduce post-operative nausea and vomiting or as cover for patients at risk of adrenal insufficiency. However, bear in mind and monitor serum potassium should continued corticosteroid treatment be necessary post-operatively.

Further information

MHRA/CHM advice: Polyethylene glycol (PEG) laxatives and starch-based thickeners: potential interactive effect when mixed, leading to an increased risk of aspiration (April 2021)

Addition of a macrogol (PEG)-based laxative to a liquid that has been thickened with a starch-based thickener may counteract the thickening action, resulting in a thin watery liquid that, when swallowed, increases the risk of potentially fatal aspiration in patients with dysphagia. Healthcare professionals are advised to avoid directly mixing macrogol-based laxatives with starch-based thickeners, especially for patients with dysphagia who are considered at risk of aspiration.


Summary of Product Characteristics – Duphalac® (lactulose) 3.335g/5ml Oral Solution. Mylan. Accessed via 26/09/21 [date of revision of the text August 2020]

Summary of Product Characteristics – Compound Macrogol Oral Powder Sugar Free. Galen Limited. Accessed via 11/08/2021 [date of revision of the text December 2018]

Macrogols. In: Brayfield A (Ed), Martindale: The Complete Drug Reference. London: The Royal Pharmaceutical Society of Great Britain. [Accessed 26th August 2021]

Lactulose. In: Brayfield A (Ed), Martindale: The Complete Drug Reference. London: The Royal Pharmaceutical Society of Great Britain. [Accessed 26th August 2021]

Joint Formulary Committee. British National Formulary (online) London: BMJ Group and Pharmaceutical Press [Accessed 11th August 2021]

Baxter K, Preston CL (eds), Stockley’s Drug Interactions (online) London: Pharmaceutical Press. [Accessed 26th August 2021]