Painkillers linked to antimicrobial resistance

By Rebecca Jenkins

Two commonly used pain medications – ibuprofen and acetaminophen – are contributing to the development of antimicrobial-resistant organisms, Australian research suggests.

Antibiotic overuse was known to be a primary driver of antimicrobial resistance, but emerging evidence suggested that nonantibiotic medications might also play a role, researchers wrote in npj Antimicrobials and Resistance.

The concern around nonantibiotic medicines was particularly relevant in residential aged care settings, they added, where nonantibiotic medications and antibiotics were often prescribed.

Using in-vivo testing, researchers investigated the effect of nonantibiotic medicines together with the broad-spectrum antibiotic ciprofloxacin on the growth and antimicrobial resistance of two strains of Escherichia coli (E. coli BW25113 and E. coli 6146).

They chose to investigate nine medications commonly used by older adults: ibuprofen, diclofenac, acetaminophen, furosemide, metformin, atorvastatin, tramadol, temazepam, and pseudoephedrine.

Ciprofloxacin, they noted, was not only a known inducer of mutations but was also used to treat urinary tract infections, one of the most common types of bacterial infection.

Testing showed that when the strains of E. coli were exposed to ciprofloxacin together with ibuprofen or acetaminophen, they displayed a higher frequency of genetic mutations linked to antimicrobial resistance than when they were exposed to the antibiotic alone.

‘Our findings highlight the potential for E. coli to develop mutations leading to [antimicrobial resistance] following exposure to [nonmicrobial medications] and ciprofloxacin in [residential aged care facilities] where medications are widely used,’ the researchers concluded.

Senior author Associate Professor Rietie Venter, Senior Lecturer and Head of Microbiology in the School of Pharmacy and Medical Sciences at the University of South Australia, Adelaide, said whole-genome sequencing showed there were two different types of genetic mutations observed in the E. coli bacteria.

‘One type of mutation caused a change in the target for ciprofloxacin so that the antibiotic did not work anymore,’ she told Medicine Today.

The second type of mutation caused an increase in the amount of drug efflux pumps, which act as microbial gatekeepers.

‘These drug efflux pumps remove many different antibiotics from the bacterial cell so that they cannot reach toxic levels,’ she said. ‘This type of mutation is concerning as it provides resistance to multiple classes of antibiotics.’

Professor Venter said the research also found coexposure to two nonantibiotic medications further amplified mutation rates and resistance levels.

‘Our study highlights an often-overlooked contributor to antimicrobial resistance and underscores the importance of reassessing polypharmacy risks in aged care settings,’ she said.

However, further research was needed to assess ways to mitigate these risks – e.g. the use of different painkillers or by delaying the administration of antibiotic and painkillers within a few hours of each other, she noted.

Professor Venter said there was also interest in studying the effects of other types of medications that are often administered together with antibiotics, such as cancer chemotherapy, where it was suspected antimicrobial resistance development was also ‘turbocharged’.

npj Antimicrob Resist 2025: 3: 73; doi.org/10.1038/.s44259-025-00144-w.