A colorimetric method for the evaluation of anti-giardial drugs in vitro

► This study aim to develop a simple and reliable method to determine the viability of Giardia intestinalis after incubation with an anti-giardial agent by using a colorimetric method. ► Giardia intestinalis trophozoites are cultured in 96-well plate, fixed, stained with 0.1% methylene blue and the intensity of dye is determined by microplate reader. ► OD values from the unwashed wells before fixing with methanol were significantly higher than that from the washed wells. ► A better result was obtained when the fixed trophozoites were carefully washed by immersing the whole plate into the washing solution at each step. ► The IC50 and IC90 of metronidazole, ornidazole and furazolidone as calculated from our method and the conventional method are comparable.