Which of the following is not a treatment for roundworms?

Flagyl, also known as metronidazole, is primarily an antibiotic used to treat infections caused by certain bacteria and parasites, particularly protozoa. It is effective against organisms like Giardia lamblia and anaerobic bacteria, but it is not designed to target roundworms, which belong to a different category of parasites.

On the other hand, Piperazine, Nemex, and Droncit are specifically designed to treat parasitic infections including roundworms. Piperazine is a commonly used antihelminthic that paralyzes the worms, allowing them to be expelled from the host's body. Nemex is a brand name for pyrantel pamoate, which is also effective against roundworms and works by causing paralysis in the parasites. Droncit, while primarily for tapeworms, can sometimes be mentioned in discussions of broader deworming treatments, but it is not effective against roundworms. The correct response identifies Flagyl as irrelevant for treating roundworm infections specifically.