Ibuprofen and acetaminophen (paracetamol) are common over-the-counter medications that many people reach for when sick. But research from the University of South Australia shows that these trusted staples are quietly fueling one of the world's biggest health threats: antibiotic resistance. In the first study of its kind, researchers found that ibuprofen and acetaminophen are not only driving antibiotic resistance when used individually but amplifying it when used together.

Assessing the interaction of non-antibiotic medications, the broad-spectrum antibiotic ciprofloxacin, and Escherichia coli (E. coli) -- a common bacterium that causes gut and urinary tract infections -- researchers found that ibuprofen and acetaminophen significantly increased bacterial mutations, making E. coli highly resistant to the antibiotic. "It's an important finding that has serious health implications, particularly for people in aged care homes, where multiple medications are regularly administered," the authors write. The findings also raise important questions about the risks of polypharmacy in long-term care.

The researchers assessed nine medications commonly used in senior living and long-term care: ibuprofen (an anti-inflammatory pain reliever), diclofenac (an anti-inflammatory to treat arthritis), acetaminophen (paracetamol for pain and fever), furosemide (for high blood pressure), metformin (for high sugar levels linked to diabetes), atorvastatin (to help lower cholesterol and fats in the blood), tramadol (a stronger pain medication post-surgery) , temazepam (used to treat sleeping problems), and pseudoephedrine (a decongestant).

"When bacteria were exposed to ciprofloxacin alongside ibuprofen and acetaminophen, they developed more genetic mutations than with the antibiotic alone, helping them grow faster and become highly resistant. Worryingly, the bacteria were not only resistant to the antibiotic ciprofloxacin, but increased resistance was also observed to multiple other antibiotics from different classes," said associate professor Rietie Venter, PhD.

"This doesn't mean we should stop using these medications," she said, "but we do need to be more mindful about how they interact with antibiotics -- and that includes looking beyond just two-drug combinations."

To download the full study, published in npj Antimicrobials and Resistance, click here