Scientists from the University of South Australia have found that two of the world’s most commonly used painkillers—ibuprofen and acetaminophen (also called paracetamol)—could be quietly making antibiotic resistance worse.
Even more concerning, when these two drugs are used together, they may make bacteria even more resistant than when used separately.
This important discovery, published in the journal npj Antimicrobials and Resistance, could have major health implications, especially for people in aged care homes who often take multiple medications every day.
Antibiotic resistance is one of the biggest threats to public health around the world. According to the World Health Organization, it caused over 1.2 million deaths in 2019. It happens when bacteria develop the ability to survive even when treated with antibiotics. Over time, this makes common infections harder to treat and puts lives at risk.
In this study, researchers looked at how ibuprofen and acetaminophen affect a type of bacteria called E. coli. This bacteria can cause infections in the stomach and urinary tract. They also tested ciprofloxacin, a common antibiotic used to treat these types of infections.
When E. coli was exposed to ciprofloxacin along with the painkillers, it changed more quickly and became much stronger against the antibiotic. In fact, the bacteria didn’t just resist ciprofloxacin—they also became harder to kill with several other antibiotics from different drug families.
Associate Professor Rietie Venter, who led the study, explained that the combination of pain medications and antibiotics gave the bacteria an advantage. It caused the bacteria to develop more mutations and triggered their natural defense systems, making it easier for them to push the drugs out and survive.
The researchers studied nine drugs often used in aged care: ibuprofen, acetaminophen, diclofenac (for arthritis), furosemide (for high blood pressure), metformin (for diabetes), atorvastatin (to lower cholesterol), tramadol (strong painkiller), temazepam (for sleep), and pseudoephedrine (for nasal congestion).
While ibuprofen and acetaminophen showed the strongest effect, the study highlights how many everyday drugs might influence antibiotic resistance.
Older people are more likely to take a mix of these medications every day. This is called polypharmacy. While taking different drugs is often necessary to manage multiple health conditions, this study shows it may also be helping bacteria become stronger.
Assoc Prof Venter says that this doesn’t mean we should stop using these common painkillers. Instead, it’s a reminder to be careful when combining them with antibiotics—especially for people on long-term medication plans, like those in aged care.
She added, “Antibiotic resistance isn’t just about using too many antibiotics anymore. We now see that even non-antibiotic drugs can play a role.”
The research team is now calling for more studies to explore how drug combinations affect bacteria and to better understand how regular medicines might reduce the power of antibiotics. This knowledge could lead to safer treatment plans and help fight back against antibiotic resistance worldwide.
The study is published in npj Antimicrobials and Resistance.
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