米国に住んでいればご存じの

Bismuth Subsalicylate
COMMON BRAND NAME(S): Pepto-Bismol, Pink Bismuth
Uses
This medication is used to treat occasional upset stomach, heartburn, and nausea. It is also used to treat diarrhea and help prevent travelers' diarrhea. It works by helping to slow the growth of bacteria that might be causing the diarrhea. This product should not be used to self-treat diarrhea if you also have a fever or blood/mucus in the stools. These could be signs of a serious health condition. Consult your doctor promptly for proper evaluation and treatment if you have these symptoms.
は、便の出血、熱がない場合には有効。

//www.medicinenet.com/
でも、
How is travelers' diarrhea treated?
Although prophylactic antibiotics (antibiotics taken before the person is exposed to the pathogen) are effective in preventing travelers' diarrhea, they generally are not recommended. The side effects of antibiotics, including photosensitivity・・・
効く可能性はあるが、副作用の点から（濫用は書かれていない）勧めないとあります。
Bismuth subsalicylate (Pepto-Bismol) in liquid or pill form also has been shown to be effective in preventing diarrhea in up to 65% of travelers although Pepto-Bismol may cause black stools and, rarely, ringing in the ears. People allergic to aspirin should avoid Pepto-Bismol.

When treating afflicted individuals, drugs that alleviate symptoms as well as antibiotics play a role. With moderate symptoms, the addition of Pepto-Bismol alone may suffice. Alternatively, anti-diarrheal agents such as diphenoxylate and atropine (Lomotil) or loperamide (Imodium) can be given. With severe disease, characterized by frequent diarrhea or dehydration, or complicated by the passage of bloody stools, Lomotil or Imodium should not be used and you should consult your doctor.

このサイトは、他にも、
What causes travelers' diarrhea?
Travelers' diarrhea usually is contracted by the ingestion of contaminated food or water. Contrary to common belief, food - not water - is the primary cause. The CDC estimates up to 80% of cases of travelers' diarrhea are caused by bacteria. The most common bacterium that causes travelers' diarrhea is enterotoxigenic E. coli, one of six classes of enterovirulent E. coli.
原因は水ではなく食品、8割が細菌で、ほとんどが大腸菌だが、以下に地域によって異なるとあり、
Other bacterial species implicated in travelers' diarrhea include Campylobacter jejuni, Shigella, and Salmonella. Viruses (including Rotavirus, Norwalk virus and other enteric viruses) less commonly are causes of travelers' diarrhea. Parasitic infections are an uncommon cause with the exception of Giardia lamblia, which should be suspected in individuals traveling to Russia or to mountainous regions of the Northern Hemisphere. Cryptosporidum, another parasite, also has been implicated as a common cause of diarrhea in visitors to St. Petersburg, Russia.ウイルスは勿論のこと、ロシアでは寄生性鞭毛虫も居るので、当然、細菌以外には抗生物質は効かない。ウイルス感染で生死の間を彷徨っているかのような状態で、暢気に抗生剤をひたすら飲むのは、本当に生死の問題に関わること。

なお、日本では聖書のような扱いの正露丸の成分はフェノール類ですので、BISMUTH SUBSALICYLATEとは全く異なります。