Potentially Harmful Interaction between Polyethylene Glycol Laxative and Starch-Based Thickeners

INCIDENT DESCRIPTION

PEG 3350 laxative, to be dissolved in liquid, was prescribed to treat constipation in a hospital inpatient. The patient was switched to a thickened diet for dysphagia, therefore PEG 3350 was mixed in a starch-based prethickened juice. On the second day of administration, the patient was noted to be very “gurgly”, a possible sign of aspiration, after swallowing the dose. The patient passed away a couple of hours later, following suspected aspiration during repositioning. As the patient had multiple comorbidities and a guarded prognosis, it is difficult to determine the cause of death, however, aspiration may have been a contributing factor.

BACKGROUND

Thickened liquids are commonly taken by patients with symptoms of dysphagia. Some ready-to-use thickened products are available for purchase (i.e., prethickened by the manufacturer, usually by the addition of a starch-based thickener). Alternatively, liquids can be thickened just before consumption by adding a thickening powder.¹ Such powders may be either starch-based¹ (e.g., with cornstarch) or gum-based (e.g., with xanthan gum).² The first commercially available thickeners were starch-based, and these products are effective and economical. Xanthan gum–based products were introduced later to address the cloudy appearance and caloric content of starch-thickened liquids, but they are more expensive.³

PEG laxative products are available as powders that must be dissolved in a liquid before administration. Addition of PEG laxative to a liquid that has been thickened with a starch-based thickener will result in a mixture that is thin and watery, effectively undoing the intended act of thickening. Patients with dysphagia who swallow the thinner-than-expected liquid are potentially at increased risk of aspiration. In a previously published case report, addition of PEG laxative powder to starch-thickened liquids resulted in a loss of viscosity, however when the powder was added to a liquid thickened with a xanthan gum–based product, no loss of viscosity occurred.⁴

DISCUSSION

Analysis of this incident identified several potential contributing factors:

• There was no on-screen alert about the interaction between the prescribed PEG laxative and the ordered thickener product when these orders were entered in the hospital’s computerized order entry system, for one of the following reasons:
  • the interaction could not be electronically recognized because the medication order system was separate from (i.e., did not communicate with) the systems used for dietary/speech language pathology orders;
  • the departmental systems were connected, but the interaction between PEG laxative and starch-based thickeners is novel and had not been added as an alert.
•  The healthcare provider preparing and administering the mixture was unfamiliar with the appearance of different types of thickened liquids. In particular, the change in consistency after the PEG laxative was added, from thickened to thin and watery, went unnoticed.

RECOMMENDATIONS

Manufacturers

• Add information about the interaction between PEG and starch-based thickeners to PEG laxative product monographs.
• Add a cautionary statement to the labels for starchbased prethickened products to indicate that PEG laxatives must not be added.
• Label starch-based thickening powders to indicate that these cannot be used to thicken PEG-containing mixtures.

Healthcare Facilities

• Where possible, establish an electronic interface to connect the order entries in all medication and health-related computer order systems.
• Update the computerized alert system to include the interaction between PEG laxatives and starchbased thickeners. This interaction alert should be visible to the following personnel:
  • prescribers and other healthcare providers that input orders at the point of order entry
  • pharmacists at the point of order verification and dispensing
  • nurses and other healthcare providers at the point of preparation and administration
• For patients who are taking thickened liquids and who require a PEG laxative, consider supplying the PEG powder and the xanthan gum–based thickener together as a “kit” or combo-pack. Ensure that the patient-specific kit label includes directions such as “Use only the provided xanthan gum-based thickener”.
• Advise healthcare providers (including prescribers, dietitians and speech language pathologists) to consider and warn about this interaction when making recommendations about texture of diet or use of thickeners.
• Consider labelling PEG powders to caution that the beverage into which the product is mixed must not contain a starch-based thickener. For example, include wording such as “for patients with dysphagia, PEG laxative may be added only to liquids thickened with xanthan gum–based thickener.”
• Request that the purchasing department order and maintain an adequate stock of xanthan gum–based thickeners to meet the needs of patients with dysphagia. These products should be clearly labelled and stored separately from starch-based thickeners.
• Educate front-line staff and patients/families about the potential for harm if a patient with dysphagia receives PEG laxative dissolved in a liquid thickened with a starch-based thickener. Highlight the importance of conducting a visual check of the thickened product’s texture before administering it to a patient with dysphagia.

Community-Based Healthcare Providers

• Before prescribing or recommending non-prescription PEG laxatives, determine whether the patient has dysphagia and uses starch-based thickeners. Specifically ask the patient (or caregiver) about the use of thickened liquids and counsel about avoiding the interaction between PEG laxatives and starch-based thickeners.
• If thickening agents are stocked in the pharmacy, keep a supply of both xanthan gum-based and starch-based thickeners, to provide a safe option for patients who are using thickened liquids and who also require a PEG laxative to manage their constipation.

CONCLUSION

Although the use of either PEG laxative powder or starch-thickened liquid is relatively safe, co-administration of these two products can be harmful for patients with dysphagia. Constipation and dysphagia are more common in elderly patients, and awareness of this interaction can thus reduce the potential risk of harm in this vulnerable population. Manufacturers, healthcare facilities, and community-based healthcare providers must be made aware of this novel interaction and take steps to reduce its occurrence.