MBX-4191

MBX-4191 is a pyranopyridine small molecule efflux pump inhibitor (EPI) developed to address antibiotic resistance in Gram-negative bacteria. It specifically targets the AcrB efflux pump, a primary component of the Resistance-Nodulation-Division (RND) family of transporters in *Escherichia coli* and other Enterobacteriaceae. While MBX-4191 does not possess intrinsic antibacterial activity, it functions as an adjunctive therapy by blocking the extrusion of antibiotics from the bacterial cell. This mechanism significantly potentiates the activity of various antibiotics, most notably minocycline, as well as levofloxacin and tetracyclines. Developed by Microbiotix (now MBX Biosciences), MBX-4191 has demonstrated the ability to restore antibiotic sensitivity in multidrug-resistant (MDR) strains, including carbapenem-resistant and ESBL-producing Enterobacteriaceae, and has shown efficacy in preclinical murine sepsis models when used in combination with minocycline.