Over-the-counter medications linked to antibiotic resistance

Several weeks ago, research led by the University of Tübingen revealed that several common non-antibiotics can disrupt the gut microbiome in a similar manner to antibiotics, inhibiting useful gut bacteria and thus creating a more favourable environment for pathogenic microbes such as Salmonella. Now, separate research from the University of South Australia (UniSA) has found that over-the-counter medications such as ibuprofen and paracetamol are quietly driving antibiotic resistance — what’s more, they are amplifying it when used together.

Assessing the interaction between non-antibiotic medications, the broad-spectrum antibiotic ciprofloxacin (used to treat common skin, gut or urinary tract infections) and E. coli bacteria (which causes gut and urinary tract infections), the researchers found that ibuprofen and paracetamol significantly increased bacterial mutations, making E. coli highly resistant to the antibiotic. Published in npj Antimicrobials and Resistance, their findings have serious health implications — particularly for residents of aged care homes.

“Antibiotics have long been vital in treating infectious diseases, but their widespread overuse and misuse have driven a global rise in antibiotic-resistant bacteria,” said UniSA’s Associate Professor Rietie Venter, lead researcher on the study.

“This is especially prevalent in residential aged care facilities, where older people are more likely to be prescribed multiple medications — not just antibiotics, but also drugs for pain, sleep, or blood pressure — making it an ideal breeding ground for gut bacteria to become resistant to antibiotics.”

The study assessed nine medications commonly used in residential aged care: ibuprofen (an anti-inflammatory pain relief), 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 paracetamol, they developed more genetic mutations than with the antibiotic alone, helping them grow faster and become highly resistant,” Venter said. “Worryingly, the bacteria were not only resistant to the antibiotic ciprofloxacin, but increased resistance was also observed to multiple other antibiotics from different classes.

“We also uncovered the genetic mechanisms behind this resistance, with ibuprofen and paracetamol both activating the bacteria’s defences to expel antibiotics and render them less effective.”

Venter said the study shows how antibiotic resistance is a more complex challenge than previously understood, with common non-antibiotic medications also playing a role.

“Antibiotic resistance isn’t just about antibiotics anymore,” she said.

“This study is a clear reminder that we need to carefully consider the risks of using multiple medications — particularly in aged care where residents are often prescribed a mix of long-term treatments.

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

The researchers are calling for further studies into drug interactions among anyone on long-term medication treatment regimes, in order to gain a greater awareness of how common medications may impact antibiotic effectiveness.

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