Azithromycin & Antibiotic Resistance: COVID-19 Study Reveals Risks

The widespread use of azithromycin during the COVID-19 pandemic, often prescribed despite lacking clear evidence of benefit against the virus, appears to have triggered a rapid increase in antibiotic resistance within the respiratory tracts of hospitalized patients. A new study from UC San Francisco reveals that even a single day of azithromycin treatment can measurably alter the balance of bacteria in the nose, favoring the growth of resistant strains. This finding underscores the potential for unintended consequences when antibiotics are used inappropriately, even in the context of a global health crisis.

Azithromycin and the COVID-19 Response: A Retrospective Look

Azithromycin, a macrolide antibiotic, is a cornerstone treatment for several bacterial infections, including strep throat, certain types of pneumonia, and sexually transmitted diseases. However, it is ineffective against viruses like SARS-CoV-2, the virus that causes COVID-19. Despite this, azithromycin was frequently prescribed “empirically” – meaning it was given based on clinical suspicion rather than confirmed bacterial infection – during the early stages of the pandemic. This practice was fueled by initial, and ultimately disproven, suggestions of antiviral or anti-inflammatory properties. Research from UCSF has since demonstrated that azithromycin offers no benefit in preventing COVID-19 symptoms and may even increase the risk of hospitalization.

The recent study, published as a preprint on PubMed (Empiric Azithromycin in COVID-19 Impacts the Respiratory…), provides a detailed look at the impact of azithromycin on the respiratory microbiome – the complex community of bacteria, viruses, and fungi that live in the nose and throat. Researchers analyzed nasal swabs collected from 1,164 patients hospitalized with COVID-19 between 2020 and 2023. The cohort was divided into three groups: those treated with azithromycin (366 patients), those receiving other antibiotics (324 patients), and those receiving no antibiotics at all (474 patients). The study employed longitudinal metatranscriptomics, a sophisticated technique that allows scientists to track changes in the genetic material of the microbiome over time.

Microbiome Disruption and the Rise of Resistance

The findings revealed that azithromycin treatment led to significant alterations in the composition of the nasal microbiome. Specifically, the researchers observed a reduction in overall bacterial abundance, an increase in fungal abundance, and a rise in potentially harmful bacteria like Klebsiella and Staphylococcus. More concerningly, azithromycin exposure was strongly associated with an increase in the expression of genes that confer resistance to macrolide/lincosamide/streptogramin (MLS) antibiotics – the class of drugs to which azithromycin belongs. This increase in resistance gene expression was detectable within just one day of starting azithromycin and persisted for over a week.

The study identified specific MLS resistance genes, including ermC, msrA, and ermX, that showed the most significant increase in expression among patients receiving azithromycin. These genes enable bacteria to evade the effects of the antibiotic, rendering it ineffective. The researchers likewise found that the expression of these resistance genes correlated with the abundance of both commensal (normally harmless) and potentially pathogenic bacteria, suggesting that azithromycin can promote resistance even in bacteria that aren’t directly targeted by the drug.

What Does This Mean for Patients and Public Health?

The implications of these findings are far-reaching. The development of antibiotic resistance is a major global health threat, rendering common infections increasingly difficult – and sometimes impossible – to treat. The study highlights the importance of judicious antibiotic use, even during pandemics, and the potential for unintended consequences when antibiotics are prescribed without a clear indication. It’s crucial to remember that antibiotics target bacteria, not viruses, and their use against viral infections like COVID-19 is not only ineffective but can also contribute to the spread of antibiotic resistance.

The study did not find evidence of a corresponding increase in inflammation in the patients’ blood or airways, suggesting that the microbiome changes induced by azithromycin did not trigger a significant immune response. However, the researchers caution that this does not negate the potential long-term consequences of antibiotic resistance. As detailed in Nature Microbiology, the altered microbiome and increased resistome represent a measurable impact of empiric azithromycin treatment without any apparent clinical benefit.

Understanding Empiric Treatment and its Risks

“Empiric” antibiotic treatment refers to the practice of prescribing antibiotics based on a clinical suspicion of bacterial infection, before the results of laboratory tests are available. While sometimes necessary in life-threatening situations, empiric treatment carries the risk of inappropriate antibiotic use, particularly when the infection is likely viral. The COVID-19 pandemic saw a surge in empiric azithromycin prescriptions, driven by a combination of factors, including uncertainty about the virus, a desire to provide supportive care, and early, flawed studies suggesting potential benefits.

Looking Ahead: Surveillance and Stewardship

The findings from this study reinforce the need for robust antibiotic stewardship programs in hospitals and healthcare settings. These programs aim to optimize antibiotic use, reduce inappropriate prescribing, and minimize the development of antibiotic resistance. Ongoing surveillance of the respiratory microbiome and resistome can help track the emergence and spread of resistance genes, informing public health interventions.

Further research is needed to fully understand the long-term consequences of azithromycin-induced microbiome changes and the impact on patient outcomes. Clinical trials are underway to evaluate alternative strategies for managing respiratory infections, including antiviral therapies and immunomodulatory approaches. The World Health Organization (WHO) continues to emphasize the importance of responsible antibiotic use as a critical component of global efforts to combat antibiotic resistance.

Next Steps: Public health agencies are reviewing existing guidelines for antibiotic use in respiratory infections, with a focus on minimizing inappropriate prescribing. Continued monitoring of antibiotic resistance patterns will be essential to inform future policy decisions and ensure the effectiveness of available treatments.