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

Addition of a polyethylene glycol (PEG)-based laxative to a liquid that has been thickened with a starch-based thickener may counteract the thickening action, placing patients with dysphagia at a greater risk of aspiration.From:Medicines and Healthcare products Regulatory AgencyPublished:27 April 2021Therapeutic area:GI, hepatology and pancreatic disorders


  1. About polyethylene glycol (PEG) laxatives
  2. About starch-based thickeners
  3. Reports of a potentially harmful interactive effect
  4. Report any suspected adverse drug reactions

Advice for healthcare professionals:

  • there have been reports of a possible potential harmful interaction between polyethylene glycol (PEG) laxatives and starch-based thickeners when they are mixed together
  • combining the two compounds can counteract the thickening action and result in a thin watery liquid — patients with swallowing difficulties (dysphagia) are potentially at greater risk of aspiration of the thinner liquid
  • avoid directly mixing together PEG laxatives and starch-based thickeners, especially in patients with dysphagia who are considered at risk of aspiration such as elderly people and people with disabilities that affect swallowing
  • report suspected adverse drug reactions (ADRs) to the Yellow Card Scheme

About polyethylene glycol (PEG) laxatives

Polyethylene glycol (PEG) laxative products treat constipation through an osmotic effect. They are indicated mostly for adults with some formulations also indicated for use in children. Some PEG laxative products such as Movicol, Macrogol 3350, and Moviprep are available in the form of a powder, which must be dissolved in liquid before administration.

About starch-based thickeners

Thickened liquids are usually taken by patients with dysphagia, including people who are elderly or have disabilities that affect swallowing. Thickening the liquid before swallowing improves bolus control and reduces the risk of aspiration, which can be life-threatening.

There are two main types of thickening agents – a starch-based (for example, corn-starch) or a gum-based (xanthan gum). Most thickeners are classified as foods for special medicinal purposes and are used to thicken both liquids and foods to various consistencies. There are many different brands of thickeners available and they can be in the form of powder or a liquid.

The recommendation to use a thickener should be based on the patient’s degree of dysphagia (and potential risk of aspiration), the desired consistency required, the texture required, palatability, and other clinical considerations (see guidance from the Specialist Pharmacist Service).

Reports of a potentially harmful interactive effect

The Institute for Safe Medication Practices (ISMP) Canada issued a Safety Bulletin discussing the possible potential harmful interaction between PEG laxative and starch-based thickeners. One case report was identified where a patient was switched to a thickened diet for dysphagia. PEG-3350 was mixed with a starch-based pre-thickened juice. On day 2 of administration the patient showed possible signs of aspiration after swallowing the dose. The patient died a few hours later. Although the cause of death was difficult to establish due to the patients underlying medical conditions, aspiration was thought to have been a contributing factor.

Addition of a PEG laxative to a liquid that has been thickened with a starch-based thickener can produce a mixture that is thin and watery – undoing the intended act of thickening. Patients with dysphagia who swallow the thinner liquid are potentially at greater risk of aspiration.

Constipation and dysphagia coexist more commonly in the elderly and in people with disabilities that affect swallowing. Therefore these populations may be of particular risk if a PEG laxative is added to liquid thickened with starch. The MHRA is currently not aware of any case reports of this potential interaction in the UK.

We have requested that the manufacturers of UK PEG laxative products add information about the potential interactive effect to the Summary of Product Characteristics and the Patient Information Leaflet.

Report any suspected adverse drug reactions

Please continue to report suspected adverse drug reactions via the Yellow Card scheme. Your report will help us safeguard public health.

Healthcare professionals, patients, and caregivers are asked to submit reports using the Yellow Card scheme electronically using:

When reporting please provide as much information as possible, including information about batch numbers, medical history, any concomitant medication, onset, treatment dates, and product brand name.

Article citation: Drug Safety Update volume 14, issue 9: April 2021: 1.

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