Pipemidic acid is an antibiotic and derivative of piromidic acid . It is active against clinical isolates of E. coli, P. mirabilis, P. inconstans, Shigella, Salmonella, Alcaligenes, and V. parahaemolyticus (MICs = 0.78-100 µg/ml), as well as drug-resistant clinical isolates of E. coli, P. mirabilis, Klebsiella, and Shigella (MICs = 1.56-6.25 µg/ml). Pipemidic acid is protective against systemic S. aureus, E. coli, K. pneumoniae, and P. aeruginosa infections in mice (EDs = 237.5, 204.1, 28.6, and 99.5 mg/kg, respectively). It is also protective against P. aeruginosa-induced pulmonary and dermal infections (EDs = 81.7 and 173.2 mg/kg, respectively), as well as E. coli, K. pneumoniae, and P. aeruginosa urinary bladder infections (EDs = 4.8, 11.9, and 30.6 mg/kg, respectively), in mice.