In vitro inhibition of Giardia lamblia and Trichomonas vaginalis growth by bithionol, dichlorophene, and hexachlorophene.

Bithionol, dichlorophene, and hexachlorophene, which are used in treating some helminthic infections, killed trophozoites of Giardia lamblia and Trichomonas vaginalis in modified BI-S-33 and Asami media, respectively. Virtually all G. lamblia and T. vaginalis cells were killed within 24 h with a 0.42 mM concentration of these compounds, except that 0.93 mM dichlorophene was required for sterilizing T. vaginalis in the same period. In modified BI-S-33 and Asami media from which bovine and human sera were omitted, respectively, the inhibitory actions of the compounds against in vitro growth of these protozoa were significantly enhanced. Trophozoites of G. lamblia and T. vaginalis could be killed in shorter than 10 min with 0.074 mM dichlorophene and 0.0025 mM hexachlorophene, respectively, in serum-free media. G. lamblia, which was incubated in the complete medium containing dichlorophene, showed a characteristic swelling of the ventral side which led to disruption of the parasite, whereas bithionol caused a thin crack in the cytoplasm of T. vaginalis incubated in Asami medium. The crack appeared to enlarge and result in vacuolization of T. vaginalis. These observations suggest that bithionol, dichlorophene, and hexachlorophene merit further evaluation to ascertain whether they are useful for treatment of giardiasis and trichomoniasis.