LAUSR

&NA; Treatment of toxoplasmosis is necessary in congenital form and immunocompromised patients. Atovaquone is a powerful suppressor of protozoan parasites with a broad‐spectrum activity, but an extremely low water solubility and bioavailability. In this study, nanoemulsion of this drug was prepared with grape seed oil using spontaneous emulsification method to increase bioavailability and efficacy of atovaquone for treatment of toxoplasmosis. In vitro activity of atovaquone nanoemulsion against T. gondii, RH and Tehran strains, was assessed in HeLa cell culture. For in vivo assessment, BALB/c mice were infected with RH and Tehran strains and then treated with nanoemulsion of atovaquone, compared to that treated with free atovaquone. Concentration of atovaquone nanoemulsion showed in vitro anti‐parasitic effects in both strains of T. gondii. Furthermore, oral administration of atovaquone nanoemulsion increased oral bioavailability, tissue distribution and mice survival time and reduced parasitemia and number and size of the brain cysts. Decrease of cyst numbers was verified by down regulation of BAG1 using real‐time polymerase chain reaction (real‐time PCR) assay. Effective therapeutic activity of atovaquone at a reduced dose is the major achievement of this study. Graphical Abstract Figure. No caption available.