The effects of the antiprotozoal drugs metronidazole and furazolidone on trophozoites of Giardia lamblia (P1 strain).

The effects of metronidazole and furazolidone on Giardia lamblia trophozoites were analyzed by video-light and transmission electron microscopy. In addition, growth curves were drawn based on four concentrations of the drugs. The IC50 was 4.6 microM for metronidazole and 2.9 microM for furazolidone. By light microscopy we observed that metronidazole-treated cells maintained the characteristic body shape, but many showed bubbles in the dorsal and ventral surfaces. The effects of furazolidone include changes in the morphology (the cells were roundish) and also cytoplasmic extrusions. When observed by transmission microscopy, cells treated with metronidazole appeared rounder than usual and membranous structures were observed in the cytoplasm. Cells treated with furazolidone showed the cytoplasm depleted of its contents and great changes in volume. Our results show that furazolidone was more effective than metronidazole and its effects were observed in cells treated with 1 microg/ml (the lowest concentration) as early as 6 h after the start of exposure.