What is the treatment of choice for Trichomonas vaginalis?

Metronidazole is the treatment of choice for Trichomonas vaginalis due to its effectiveness in targeting the protozoan responsible for the infection. Trichomonas vaginalis is a sexually transmitted parasite that can cause vaginitis in women and urethritis in men. Metronidazole works by disrupting DNA synthesis and function in the parasite, leading to its death.

It is also essential to treat the patient's sexual partner simultaneously to prevent reinfection, as Trichomonas vaginalis can be easily transmitted through sexual activity. By treating both partners, the likelihood of effective resolution of the infection in both individuals is maximized.

Other options listed do not serve to treat a Trichomonas infection. For example, 5-ASA is primarily used in inflammatory bowel disease, while praziquantel is effective against trematodes and cestodes (flatworms) but not against protozoan infections. Ivermectin is used for certain parasitic infections but is not effective against Trichomonas vaginalis. Thus, metronidazole stands out as the specific, effective treatment for this particular infection.