(Reuters Health) - Common drugs to reduce stomach acid and treat acid reflux also change the populations of microbes living in the intestines, which may help explain why they increase the risk of certain infections, according to a new study.

So-called proton pump inhibitors (PPI) like omeprazole (Prilosec) and esomeprazole (Nexium) can be available by prescription or over the counter and are among the top 10 most widely used drugs in the world. They may cause side effects like diarrhea, nausea and vomiting, and some studies have linked them with an increased risk of the Clostridium difficile infection.

Clostridium difficile, or “C. diff,” attacks the intestinal lining and causes severe diarrhea and pain.

“I think mostly general practitioners and medical doctors should be aware of these side effects,” said lead author Floris Imhann of the University of Groningen and University Medical Center Groningen in the Netherlands.

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“Individual risk (of C. diff) is fairly low,” but PPIs are widely used, and often overused, Imhann told Reuters Health by phone.

The researchers analyzed the gut bacteria compositions of 1,815 adults in the Netherlands, some who were healthy and some with gastrointestinal diseases like irritable bowel syndrome.

Participants reported their current medication use and gut complaints in a questionnaire and provided stool samples. The researchers isolated microbial DNA from the stool samples.

Just over 10 percent of the participants said they were using a proton pump inhibitor, including 8 percent of the healthy general population and 20 percent of those with inflammatory bowel disease. PPI users tended to be older and have a higher body mass index than others.

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Those using PPIs had less diversity of their gut microbes, the researchers reported in the journal Gut. They also had more bacteria usually found in the mouth and bacteria associated with infection in their stool samples.

This may be because PPIs reduce the acidity of the stomach, so more oral bacteria survive the journey from mouth to gut along with food.

Using PPIs appeared to have a greater effect on the gut “microbiome” than using antibiotics, the authors wrote.

“These PPIs, they are very good drugs, they work really well,” said senior author Dr. Rinse K. Weersma. But many people take them over the counter and about half the time, they’re not being taken appropriately, he said.

According to this study, people who take the drugs have beneficial bacteria in lower numbers and more harmful bacteria in higher numbers, he said.

“Once they are started most people do not think about stopping them,” Weersma told Reuters Health by phone.

In the Netherlands, PPIs are very widely used, and antibiotics are not as common as in the U.S., so PPIs cause a greater disturbance to the microbiome, Imhann said.

PPI use makes some infections 1.5 times as likely, he said.

“Knowledge is lacking there, the perception is still that they’re relatively safe,” Weersma said.

SOURCE: bit.ly/1MlI2fI Gut online December 9, 2015.