NEWT Guidelines - Thickening agents (2024)

Thickening agents are designed to be mixed with food and drinks in order to thicken them to a safe consistency for consumption. They are not intended to be used to administer medications.

They fall into two main groups⁹⁰²

• - starch-based thickening agents are typically maize starch. The starch molecules swell when they come in contact with water, which increases viscosity.
• - gum-based thickening agents include xanthan, guar, carob (locust bean) and carrageenan. In the UK most gum-based thickening agents contain xanthan gum. Xanthan gum forms rod-type chains sometimes described as “meshes of entanglement”, trapping water and increasing viscosity.

How to use thickening agents

Fluid consistency and food texture is graded according to the International Dysphagia Diet Standardisation Initiative (IDDSI) framework.⁹⁰² Thickened fluids can be swallowed more safely than thin fluids as they travel more slowly, allowing the patient more time to co-ordinate the swallow response.⁹⁰²

Thickening agents can be used to modify the consistency of thin liquids to IDDSI levels 1-4. They are not medicines – many of them are classed as Food for Special Medical Purposes. Some brands are listed in UK drug tariffs, and are prescribable.⁹⁰²

The choice of thickening agent depends upon patient preference, as well as their living situation. Thickened fluids can be unpalatable, with starch-based products sometimes having a starch flavour and a grainy texture, whilst gum-based thickeners can be “slicker”.⁹⁰² It is generally found that flavour and palatability deteriorate with increasing thickness regardless of the thickening agent used.⁹⁰²

Starch-thickened fluids can become thicker on standing, whilst gum-thickened fluids are slightly more stable.⁹⁰² Some products can be stored in the fridge after preparation, whereas others have to be used immediately. Each product comes with its own scoop, and these are not interchangeable. The instructions for use also differ between products, with some products advising to add powder to liquid, and others to add liquid to powder.⁹⁰² For patients with diabetes, or those on a ketogenic diet, it is important to consider the carbohydrate and sugar content of thickeners. If the patient lives with others who also require thickened fluids, such as in a care home, it is often practical to use one thickening agent for all residents.⁹⁰²

It is good practice to visually check the consistency of all fluids before they are taken to ensure that they are the appropriate thickness for the patient.⁹⁰¹

Medication interactions with thickening agents

As thickening agents are not intended for the administration of medications, there is little information about potential drug interactions; however it is known that some medications can interact with thickened fluids, altering the consistency of the fluid. For this reason adding medications to thickened fluids is generally the option of last resort and it is particularly important to visually assess the consistency of fluids to which medications have been added.

A well-reported interaction is that between macrogol laxatives and starch-thickened fluids, which results in a thin watery liquid. In 2019, the Institute for Safe Medication Practice in Canada shared an incident of this where the patient later died, possibly from aspiration.⁹⁰¹ Thickening agents based on carob gum (also called locust bean gum) are also not suitable to be mixed with macrogol laxatives,⁹⁰¹ and it is recommended that if any thickening agent is used for these medicines, it should be a xanthan gum-based agent, and the thickened liquid should be checked for consistency before being taken.⁹⁰²

Amitriptyline, tamoxifen, and verapamil have been documented as being incompatible with xanthan gum in products used to create extemporaneous liquids. It is not known whether adding the medications to thickened fluid immediately before administration would have a clinically significant interaction, but an alternative administration method should be used if possible.⁹⁰¹

Xanthan, guar, and other gum-based agents are used in some modified-release drug formulations to slow drug dissolution,⁹⁰¹ and some small studies have been done to assess the effect of thickening agents on drug dissolution.

An in vitro study of crushed tablets of amlodipine, atenolol, carbamazepine and warfarin, mixed with water, thickened water, honey, orange juice, yogurt and jam showed that drug dissolution was delayed in the thickened water compared to the other mixtures tested.⁹⁰¹ Crushed atenolol was mixed with fluids thickened with five different agents, to three different consistencies (IDDSI 2, 3 and 4). Drug dissolution was not reduced at level 2, but at level 3 drug dissolution was reduced in the xanthan gum-thickened fluids, and at level 4 drug dissolution was reduced in both starch and xanthan gum-thickened fluids.⁹⁰¹

Another study looked at various formulations of paracetamol (crushed tablets in water, effervescent tablets in water, elixir and suspension) all thickened with a xanthan gum and maltodextrin product to IDDSI level 4. The study found considerably delayed drug dissolution in all cases. Different methods of preparing the product were assessed (adding the medication to thickened fluid, adding thickening agent to the medication in water, adding water to a mixture of medication and thickener powder) but the delayed dissolution was found in all preparation methods.⁹⁰¹

These studies demonstrate the possibility of delayed onset of effect when medications are administered in thickened fluids, and that this effect may become more pronounced with higher levels of viscosity.⁹⁰⁴

For medications with a wide therapeutic range, the effect of the thickening agent on the medication may not be clinically relevant, however it is important to monitor the effect of therapy, and to ensure that medications are given consistently by the same method. An alteration in the patient’s swallowing requirements (i.e. a change in viscosity) may have an effect on both effectiveness and / or toxicity of their medication.

How to give medications to patients who require thickened fluids

• First choice – administer the medication with soft food.⁹⁰⁴
• Second choice – administer a solid dose medication with thickened fluid (crushed / opened if necessary – check the drug monographs first).⁹⁰⁴
• Third choice – administer a liquid medicine mixed with thickening agent.⁹⁰⁴

Small-volume liquid medicine doses can be thickened in two ways:⁹⁰⁴

• - the dose can be diluted in a larger volume of fluid, then thickened appropriately. There is a risk here that the whole dose might not be consumed.
• - the dose can be thickened directly by sprinkling thickening agent onto the dose. It can be difficult to assess the degree of thickness of a small volume.

Large-volume liquid medicine doses should be thickened by adding the thickening agent directly. The liquid should always be checked to ensure that the desired consistency has been obtained, and should be consumed immediately.⁹⁰⁴

Important:

• Prepare and administer each medication separately, one at a time. When medications are mixed with food or fluid, use a small volume and administer this first to ensure that the whole dose is taken.


• Do not thicken a whole bottle of liquid medicine – thicken each dose one at a time.⁹⁰⁴


• Do not used milk-based fluids to administer medications which interact with calcium ions.⁹⁰⁴


• Monitor the effect of medications, and monitor for side effects, adjusting the medicine dose if required.