The compounds include substituted rifamycin derivatives in which a quinolone carboxylic acid pharmacophore is covalently bonded to a benzoxazinorifamycin or a spiropiperidinorifamycin. The rifamycin derivatives are useful as antimicrobial agents and are effective against a number of human and veterinary Gram positive and Gram negative pathogens. The advantage of the inventive compounds is that both the rifamycin and quinolone antibacterial pharmacophores are co-delivered with matched pharmacokinetics to the targeted pathogens of interests. Delivery of multiple antibacterial pharmacophores simultaneously to the targeted pathogens has the maximum chance of achieving synergy and minimizing the development of resistance to the antibiotics given.