Bismuth subsalicylate (Pepto-Bismol) vs. Dimenhydrate (Gravol)

Question

Pharmacy Times doesn't distinguish them. familydoctor.org (sponsored by American Academy of Family Physicians) states:

• Bismuth subsalicylate (2 brand names: Kaopectate, Pepto-Bismol). It may help treat some types of nausea and vomiting, such as from gastroenteritis (stomach flu). It’s also used for upset stomach and as an antidiarrheal (medicine to treat diarrhea).
• Antihistamines. Certain types may help prevent nausea and vomiting caused by motion sickness. These include dimenhydrinate (brand name: Dramamine) and meclizine hydrochloride (brand name: Dramamine Less Drowsy).

1. The quote overhead includes more symptoms for Bismuth subsalicylate (which I've colored in grey) than Antihistamines. So does Bismuth subsalicylate help with more symptoms than Antihistamines?

2. Does Bismuth subsalicylate cover broader types of nausea and vomiting? For antihistamines, the quote overhead appears to qualify "nausea and vomiting" to "nausea and vomiting caused by motion sickness".

3. How else do these two differ?

Answer 1

Bismuth subsalicylate and antihistamines have different mechanisms of actions, so one drug is appropriate for some and another for other conditions with nausea.

Bismuth subsalicylate can "soothe" the gut by being a mild anti-inflammatory, antacid, antibiotic and anti-diarrheal, so it can reduce nausea and diarrhea in gastrointestinal conditions, for example, acid reflux, food poisoning, infections (stomach flu, H. pylori infection, etc.), irritable bowel syndrome and inflammatory diseases (see also Drugs.com and RxList).

Antihistamines, such as dimenhydrinate, inhibit the stimulation of the labyrinth in the inner ear, so they are mainly used for motion sickness and other conditions of the inner ear (viral labyrinthitis, Meniere's disease, etc.). Antihistamines are also used for nausea in (migraine, morning sickness in pregnancy, after surgery and during chemotherapy), but I'm not sure how effective they are in those cases.

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In summary, bismuth subsalicylate may help in nausea, diarrhea, upset stomach and heartburn caused by gastrointestinal conditions and antihistamines may help in inner ear conditions, including motion sickness.

The bottom line is that bismuth subsalicylate acts in the gut and antihistamines in the inner ear.