I received an inquiry on travelers’ diarrhoea. It was from a health care professional. How does Bismuth Subsalicyllate (PeptoBismol) work in travellers’s diarrhoea?

Travellers’ diarrhoea is one of the most common illnesses in people who travel internationally, and depending on destination affects 20-60% of the more than 800 million travellers each year. In most cases, the diarrhoea occurs in people who travel to areas with poor food and water hygiene.

Classic travellers’ diarrhoea (TD) is defined as at least three loose to watery stools in 24 hours with or without one or more symptoms of abdominal cramps, fever, nausea, vomiting, or blood in the stool. Mild to moderate diarrhoea is one or two loose stools in 24 hours with or without another enteric symptom. The median time to onset is six or seven days after arrival. Although the diarrhoea often resolves spontaneously over three or four days, up to a quarter of affected travellers need to alter their plans, interrupting their holiday or business activities (Hill er al. Management of travellers’ diarrhoea. BMJ. 11 October 2008. Vol.337.

The destination is the most significant risk factor for developing TD. Regions with the highest risk are Africa, South Asia, Latin America, and the Middle East. Travelers who are immuno-compromised and those with lowered gastric acidity (e.g., patients taking histamine H2 blockers or proton pump inhibitors) are more susceptible to TD.

At this point, I will be using information from a paper by Taylor et al, ” Medications for the prevention and treatment of travellers’ diarrhea.” Journal of Travel Medicine, 2017, Vol 24, Suppl 1, S17–S22.

 Preventing and treating travellers’ diarrhoea (TD) during and after a journey continue to be important clinical challenges. Bacterial pathogens such as enterotoxigenic Escherichia coli (ETEC), enteroaggregative E. coli, Campylobacter species, and Shigella spp. still predominate as causes even though viruses, parasites and other bacteria account for diarrhoeal diseases.

The problem of antimicrobial resistance adds another challenge to the empirical treatment of travellers’ bacteria. There is now increasing awareness of alterations to gutmicroflora caused by even a short course of antibiotics.

Diarrhoea is one of the most common illnesses acquired during travel. TD caused by ETEC, the most common aetiology, is usually watery diarrhoea associated with nausea, vomiting, and abdominal cramping or pain. ETEC is confined to the lumen of the gut and disease is mediated by a toxin. The spectrum of illness has been categorized as mild, moderate, or severe. Severe diarrhoea is characterized by more than 10 loose, watery stools in a single day. Moderate diarrhoea is more than a few diarrhoea stools but less than 10 diarrhoea stools in a day. Mild diarrhoea is a few diarrhoea stools in a day.

TD has been defined as three or more unformed stools or two unformed stools with at least one accompanying symptom (nausea, vomiting, abdominal pain, fever, blood in stool) within 24 hours.

The incidence of TD in resource-poor countries is never less than 20–30% of travellers and can be as high as 88%. That means the chance that a traveller will have his/her trip impacted by an episode of uncomfortable diarrhoea ranges from 1 in 5 to over 4 in 5. The concept that TD is a self-limited illness that does not require treatment is belied by the magnitude of the symptoms present in a majority of cases. Vomiting, fever, severe cramps, and blood in the stool are present in a substantial subset of travellers with acute gastroenteritis.

Bismuth subsalicylate (Pepto-Bismol) provides a rate of protection of about 60 percent against traveller’s diarrhoea. However, it is not recommended for persons taking anticoagulants or other salicylates. Because bismuth subsalicylate interferes with the absorption of doxycycline (Vibramycin), it should not be taken by travellers using doxycycline for malaria prophylaxis. Travellers should be warned about possible reversible side effects of bismuth subsalicylate, such as a black tongue, dark stools, and tinnitus.

The FDA-approved indications of BSS are for the treatment of diarrhoea, heartburn, indigestions, nausea, and stomach upset. BSS is effective in situations where patients are experiencing mild gastrointestinal discomfort, as it reduces the severity and incidence of flatulence and diarrhoea.

BSS can be found over the counter and does not require a prescription; as such, it has become a preferred self-treatment option for mild diarrhoea, replacing the need for an antimicrobial.

Bismuth subsalicylate (BSS) exhibits many of its properties due to its formulation as an insoluble salt of salicylic acid and trivalent bismuth. The mechanism of action through which BSS works is complex. In the stomach, BSS hydrolyzes into two compounds, bismuth, and salicylic acid. The salicylate compound is almost completely absorbed into the bloodstream, while bismuth salt is minimally absorbed. The bismuth that remains in the gastrointestinal tract forms other bismuth salts. These bismuth salts contain bactericidal and antimicrobial activity, and prevent bacteria from binding and growing on the mucosal cells of the stomach. It is the same mechanism by which BSS helps eradicate Helicobacter  pylori- and thus its application as an anti-ulcer agent. Furthermore, the prevention of bacterial binding to the mucosal cells provides many benefits, which include prevention of intestinal secretion, promotion of fluid absorption, reduction of inflammation, and promotion of the healing of any present ulcer in the stomach. BSS  appears  not to alter the normal flora of the stomach. BSS antimicrobial and antisecretory properties play a major role in combating diarrhoea.

The Centers for Disease Control (CDC) lists several preventive measures that may reduce the likelihood of developing TD. These include education about the avoidance of high-risk foods and beverages, good hygiene, and the use of prophylactic medications.

The best means of preventing TD is education regarding food and beverage selection, with the goal that the traveller avoid the consumption of high-risk products. The aphorism “Boil it, cook it, peel it, or forget it” remains standard preventive advice, as travellers to high-risk areas should avoid consuming untreated tap water, raw fruits and vegetables not washed by the traveller, and undercooked meats and seafood. In addition, travellers should be informed that boiled water and foods treated with iodine or chlorine may be safely consumed. Although preventive measures are recommended, travellers may not be able to adhere to the recommendations, since many factors for ensuring food safety, such as restaurant hygiene, are beyond their control.

Hand washing has been shown to reduce the incidence of diarrhoea by up to 30% in community settings. Travellers should routinely wash their hands using soap and water while preparing food, before eating, and after using the toilet. If soap and water are not available, an alcohol-based hand sanitizer containing at least 60% alcohol should be used to sterilize the hands.

Dr. Edward O. Amporful

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