A substance derived from coal tar:
Used sparingly because of its potential side effects:
Looks like its mainly used for oral thrush and topical use. Does say it has antibacterial activity but not sure how strong anti-bacterial vs anti-fungal?
Internally might cause a severe allergic reaction because of the way it stains.
The best way to reach the lower small bowel/upper colon might be to mix something with cellulose.
An example would be mixing lavender oil in cellulose powder or a psyllium/caprylic acid/olive oil cocktail. Basically any anti-fungal mixed in with fiber that will travel further into the gut. Much easier said than done though. Another idea would be undecenoic acid liquid mixed with cellulose powder. That might be worth trying.