Thickening agents and thickened fluids: do they interact with medicines?

Karoline Brennan, Senior Medicines Information Pharmacist, North West Medicines Information CentrePublished

This Medicines Q&A considers interactions between medicines and thickening agents or thickened fluids used in dysphagia (swallowing difficulties).

  • Thickening agents can be starch- or gum-based. Some drug interactions are specific to a type of thickener; some are common to all.
  • Macrogol laxatives must not be mixed with starch-based thickening agents, as macrogol opposes the thickening effect of the starch, resulting in a thin liquid. This interaction has been implicated in a patient death. However, macrogol laxatives can be mixed with xanthan gum-based thickening agents.
  • Thickened fluids may delay or reduce the absorption of medicines, particularly when very thick. This may be more problematic with xanthan gum-based than starch-based thickeners, but available data are limited.
  • Where medicines have a wide therapeutic range, changes in absorption when mixed with thickened fluid immediately before administration are unlikely to be clinically relevant.
  • Where medicines have a narrow therapeutic range, if the patient is consistent in the way they take the medicine, with regards to the food or thickener used to achieve the desired consistency, changes in absorption may be managed by clinical monitoring for effect and dose adjustment if necessary.

This Medicines Q&A complements two others: