Is a common antibiotic being overlooked for the treatment of multi-drug resistant bacterial infections? Research published in the journal EBioMedicine suggests that azithromycin may be an effective therapy against Gram-negative bacteria after all.

While previous research found that azithromycin was not effective against Gram-negative bacteria in standard laboratory media, the infection is located in the blood and body tissues of humans. Victor Nizet, MD, professor of pediatrics and pharmacy at the University of California, San Diego School of Medicine and Skaggs School of Pharmacy and Pharmaceutical Sciences, and colleagues proposed that using mammalian tissue culture media, rather than bacteriologic media, could lead to different results.

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Promising initial findings showed that azithromycin eliminated Pseudomonas aeruginosa, Klebsiella pneumonia, and Acinetobacter baumannii in mammalian tissue culture media and were 100% effective when combined with colistin or antimicrobial peptides produced naturally by the human body during infection. Using an animal model, mice treated with single injected dose of azithromycin at a dose that mimics the amount typically administered via IV to humans led to elimination of 99% of the multidrug-resistant A. baumannii pneumonia in the lungs only 24 hours after infection. In mouse models of multi-drug resistant P. aeruginosa and K. pneumoniae infections, one azithromycin dose lowered bacterial counts over 10-fold.

Based on this study, the authors suggest that there has been complacency over the years with regards to antibiotic evaluation, and that testing already approved antibiotics under different conditions may provide better insight on their effectiveness towards multi-drug resistant pathogens.

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