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Medicines used for pain relief, diabetes and hormone replacement can increase the tendency for bacteria to develop genes needed to resist antibiotic treatments, when combined with an antibiotic commonly found in UK waterways, study results have shown.
Publishing their findings in ISME Communications on 14 October 2025, researchers from the University of Exeter spiked single concentrations of diclofenac, metformin and 17-β-estradiol with the commonly-used antibiotic ciprofloxacin — often found in high concentrations in freshwater sources across the world — at a range of low concentrations that are typical in the environment.
The study results revealed that when the medicines were combined with ciprofloxacin, they were more likely to lead to an increase in specific antibiotic resistance genes compared with when these bacteria were exposed to the antibiotic alone.
Lead researcher April Hayes, post-doctoral research fellow and microbiologist at the University of Exeter, said: “We’ve found that the kind of common medications that many people might routinely take can form a pharmaceutical cocktail in the environment and our waterways that promotes antibiotic resistance.
“This poses a potential threat to human health because if we then ingest these bacteria and are infected, we may not be able to easily treat them, as antibiotics are more likely to fail. Antimicrobial resistance (AMR) is a growing global problem — and these mixtures might form an important contribution to that problem.”
On 13 October 2025, a report published by the World Health Organization (WHO) revealed that one in six laboratory confirmed bacterial infections that caused common infections in people worldwide in 2023 were resistant to antibiotic treatments.
Between 2018 and 2023, AMR rose in more than 40% of the pathogen-antibiotic combinations monitored, with an average annual increase of 5–15%, the report found.
It also showed that drug-resistant Gram-negative bacteria are becoming more dangerous worldwide, with the greatest burden falling on countries least equipped to respond.
In a press release published alongside the report, the WHO said: “Among these, Escherichia coli and Klebsiella pneumoniae are the leading drug-resistant Gram-negative bacteria found in bloodstream infections. These are among the most severe bacterial infections that often result in sepsis, organ failure and death.”
However, more than 40% of E. coli and 55% of K. pneumoniae globally are now resistant to third-generation cephalosporins, which is the first-choice treatment for these infections.
WHO’s statement said: “Other essential life-saving antibiotics, including carbapenems and fluoroquinolones, are also losing effectiveness against E. coli, K. pneumoniae, Salmonella, and Acinetobacter.
“Carbapenem resistance, once rare, is becoming more frequent, narrowing treatment options and forcing reliance on last-resort antibiotics.”
Commenting on the University of Exeter’s research, Jef Grainger, programme lead for tackling infections at UK Research Innovation (UKRI) and associate director at the Biotechnology and Biological Services Research Council, which supported the study, said: “UKRI has identified tackling infections as one of its five strategic themes, with AMR recognised as a flagship challenge.
“This research deepens our understanding of how resistance develops, not just through antibiotics, but through combinations of drugs commonly found in the environment. These findings highlight the urgent need to consider pharmaceutical mixtures in AMR research and policy, helping to shape more effective interventions.”
In response to a question on what the Environment Agency is doing to tackle AMR in waterways, a spokesperson for the Department for Environment, Food and Rural Affairs (DEFRA) said: “The Environment Agency (EA) has undertaken research in relation of the environmental dimension of AMR and most recently under the cross-governmental PATH-SAFE programme.
“Through PATH-SAFE, the EA worked with DEFRA and the UK Health Security Agency, to understand how we would measure AMR in the environment but also understand what levels of antimicrobials can drive the development of resistance.”
“Further work on AMR remains ongoing,” they added.
In August 2024, a study revealed that active pharmaceutical ingredients, including carbamazepine and metformin, were present in 52 out of 54 river sites across ten national parks in England, which raised AMR concerns.
