Fluoxetine and Antibiotic Resistance: Key Ingredient in Antidepressants Linked to Rise of Superbugs

An ingredient in many commonly used antidepressants could be helping bacteria to develop resistance to antibiotics, according to a study published in the journal Environment International.

Antibiotic resistance is one of the biggest threats to global health, food security and development in the world today. Most significantly, it has led to the rise of "superbugs," or strains of bacteria which are resistant to several treatments.

While the misuse and overuse of antibiotics is chiefly to blame, other factors may be contributing to the problem. Now, a team led by Jianhua Guo from the University of Queensland in Australia has identified the previously unknown role of fluoxetine—a prescription drug used to help people recover from depression, obsessive-compulsive disorder and eating disorders—in this process.

According to Guo, little is known about how nonantibiotic pharmaceuticals can also cause antibiotic resistance.

"Our previous study reported that triclosan, a common ingredient in toothpaste and hand wash can directly induce antibiotic resistance," he said in a statement. "We also wondered whether other nonantibiotic pharmaceuticals such as fluoxetine can directly induce antibiotic resistance."

For the study, the scientists exposed E. coli bacteria to fluoxetine in the lab. This promoted mutations in the bacteria which left them resistant to several antibiotics, including chloramphenicol, amoxicillin and tetracycline. They found that the higher the exposure concentration of fluoxetine, the faster the mutation frequency increased with time.

"This discovery provides strong evidence that fluoxetine directly causes multi-antibiotic resistance via genetic mutation," Guo said.

When fluoxetine is ingested, up to 11 percent of the substance remains unchanged as it passes through the body and is expelled via urine into the sewer systems. Because of this, Guo suggested that fluoxetine could allow antibiotic resistance to develop in a real-world environment.

"Fluoxetine is a very persistent and well-documented drug in the wider environment, where strong environmental levels can induce multi-drug resistance," Guo said.


The researchers said that fluoxetine may also cause resistance to develop inside the human gut, although further research is required to investigate its effects there.

Around 700,000 people die every year as a result of infections caused by antibiotic-resistant bacteria. That number is expected to rise to 10 million by 2050 unless urgent global action is taken.