Combining Liquid Oral Drugs with Thickener: Compatibility and Changes in Viscosity

Older adults with oropharyngeal dysphagia (OD) are unable to swallow pills safely, so some of them use liquid-formulated drugs mixed with thickeners to ensure safety. The aim of this study was to analyze the physical compatibility of a group of drugs with a thickener formulated with modified starch (Thick & Easy®). A secondary goal was to evaluate the amount of thickener needed to obtain the thickness levels 2, 3, and 4 defined by IDDSI framework for each drug. For this purpose, the rheological properties of the mixtures obtained were determined. Samples of each drug were prepared and 7, 10, and 12 g of thickener were added. Physical compatibility of the mixtures was observed; the apparent viscosity of the samples was measured using a rotational viscometer, and the results obtained were compared with the reference drug-free sample. We analyzed 45 medicinal products (38 active substances). Three drugs (almagate, ibuprofen, and macrogol) were found to be physically incompatible with the thickener and should not be mixed. Viscosity measurements indicated that clarithromycin and plantago ovata increased the viscosity of the mixture and required lower amount to achieve the target textures (110 cP, 590 cP, and 2620 cP for 7 g, 10 g, and 12 g in drug-free samples, respectively), whereas another subset reduced viscosity and required more thickener. This proved very relevant for acetylcysteine, amoxicillin, calcifediol, ferrous gluconate, fosfomycin, lactitol, lactulose, mepifiline, paracetamol, rivastigmine, sertraline, and tramadol. Measurements were below 1750 cP. Awareness of how each drug behaves when combined with thickeners is essential to avoid potential complications in OD.