Dronedarone synergizes with colistin against planktonic and biofilm forms of multidrug-resistant Gram-negative pathogens

Infections caused by multidrug-resistant Gram-negative pathogens (MDR-GNP) are associated with high mortality, prolonged hospital stays, and increased healthcare costs. The treatment of these infections is complicated by the scarcity of new antibiotics and rising resistance to existing drugs. Colistin is often considered a last-resort therapy for MDR-GNP, but its clinical use is limited by significant nephrotoxicity and neurotoxicity. These challenges highlight the need for alternative strategies to enhance the effectiveness of current antibiotics. One promising approach is the use of combination therapy, which can potentiate antimicrobial activity while mitigating toxicity. We screened ~3,400 FDA-approved compounds and identified dronedarone, an antiarrhythmic with a well-established safety profile, as a potent enhancer of colistin activity against several MDR-GNP, including <i>Pseudomonas aeruginosa</i>, <i>Acinetobacter baumannii</i>, <i>Klebsiella pneumoniae</i>, and <i>Escherichia coli</i>. The colistin/dronedarone (COL/DRO) combination restored colistin efficacy <i>in vitro</i> and significantly reduced bacterial burden in a <i>Caenorhabditis elegans in vivo</i> model. Mechanistic studies revealed that colistin disrupts the outer membrane, facilitating dronedarone entry, which then permeabilizes and depolarizes the inner membrane, leading to cell death. This synergistic mechanism likely explains the potent activity observed. Additionally, the COL/DRO combination completely eradicated preformed biofilms of all tested pathogens. These findings suggest that dronedarone may be effectively repurposed to enhance colistin therapy, offering a promising strategy to combat life-threatening infections caused by MDR-GNP.<b>IMPORTANCE</b>Antibiotic resistance in dangerous Gram-negative bacteria is a growing global health crisis, leaving doctors with very few treatment options. Colistin is often the last available antibiotic for these infections, but its effectiveness is limited by serious side effects including nephrotoxicity and neurotoxicity. Our study shows that dronedarone, a heart medication already approved for human use, can make colistin much more effective against highly resistant bacteria. By working together, these two drugs kill bacteria that neither drug can eliminate alone, including those that form hard-to-treat biofilms. The combination also proved effective in an <i>in vivo</i> infection model, showing promise beyond the laboratory. Because dronedarone has a known safety record in people, this approach could be developed more quickly than entirely new antibiotics. These findings highlight a practical strategy to repurpose existing medicines to strengthen current antibiotics and fight life-threatening, drug-resistant infections.