Tehran University of Medical Sciences Iranian Journal of Parasitology 1735-7020 16 3 2021 08 31 394 401 Joel H. Elizondo-Luévano Department of Chemistry, School of Biological Sciences, Autonomous University of Nuevo León, Ciudad Universitaria, San Nicolás de los Garza, Nuevo León, México Oscar A. Pérez-Narváez Department of Chemistry, School of Biological Sciences, Autonomous University of Nuevo León, Ciudad Universitaria, San Nicolás de los Garza, Nuevo León, México Eduardo Sánchez-García Department of Chemistry, School of Biological Sciences, Autonomous University of Nuevo León, Ciudad Universitaria, San Nicolás de los Garza, Nuevo León, México Rocío Castro-Ríos Department of Analytical Chemistry, School of Medicine, Autonomous University of Nuevo León, Monterrey, Nuevo León, México Magda E. Hernández-García Department of Chemistry, School of Biological Sciences, Autonomous University of Nuevo León, Ciudad Universitaria, San Nicolás de los Garza, Nuevo León, México Abelardo Chávez-Montes Department of Chemistry, School of Biological Sciences, Autonomous University of Nuevo León, Ciudad Universitaria, San Nicolás de los Garza, Nuevo León, México 2020 06 17 2021 05 17 Background: Parasitic infections represent one of the main public health problems in humans according to the WHO. Therefore, the need has arisen to find new treatments that can be used as an alternative cure to parasitosis. We aimed to investigate the in-vitro effects of the methanolic extract of Kalanchoe daigremontiana as well as its main component, quercetin against Entamoeba histolytica and Trichomonas vaginalis. Methods: For this purpose, the in-vitro activity of the methanol extract of K. daigremontiana also its main component, quercetin, against trophozoites of E. histolytica and T. vaginalis was evaluated, using the microassay technique. Furthermore, the antioxidant activity was determined. Finally, the cytotoxic and cytoprotective capacity was determined using the hemolysis technique. Results: The IC50 indicated that quercetin significantly (P < 0.05) inhibited the growth rate of the trophozoite stage of E. histolytica and T. vaginalis in comparison to the methanolic extract of K. daigremontiana (KalL). Also, quercetin significantly (P < 0.05) was a better antioxidant as compared with the positive control. In the evaluation of cytotoxicity effects, it could be observed that KalL as compared with quercetin exhibited more cytotoxicity against human erythrocytes. Quercetin significantly (P < 0.001) exhibited better cytoprotective activity compared to KalL. Conclusion: Both K. daigremontiana methanolic extract and quercetin alone demonstrated high antiparasitic activity against E. histolytica and T. vaginalis. However, the in-vivo efficacy of K. daigremontiana and quercetin also requires to be evaluated using an animal model. https://ijpa.tums.ac.ir/index.php/ijpa/article/view/2959 https://ijpa.tums.ac.ir/index.php/ijpa/article/download/2959/1149