Supplementary Material for: Study on Drug–Food Thickening Agents Interactions between Warfarin and Prebiotics Used for Viscosity Adjustment

Introduction: Prebiotics are widely used in nutritional supplements, with water-soluble dietary fibers used as thickeners for patients with swallowing difficulties. Interactions between thickeners and medications have been reported; however, the effects of thickeners on warfarin remain unclear. Here, we examined the interaction between warfarin and thickeners through clinical and basic research studies. Methods: The clinical research study evaluated the effects of combining warfarin and thickeners on blood coagulation, while the basic research study measured the impact of different prebiotics and mixing with gastric and intestinal fluids on warfarin concentration. Results: The clinical research study showed no significant differences in the patients' prothrombin time-international normalized ratio and warfarin sensitivity index (WSI) before and after the combination. However, the WSI decreased postcombination in half of the patients. Meanwhile, in the basic research study, a concentration-dependent decrease in the residual rate of warfarin was observed with xanthan gum, guar gum, and pectin. When mixed with artificial gastric and intestinal fluids, the residual rate decreased with xanthan and guar gum in gastric fluid and with pectin in intestinal fluid. Conclusion: Thickeners primarily composed of xanthan gum, guar gum, and pectin may reduce the effectiveness of warfarin due to drug–food interactions.