Pipemidic acid, a new antibacterial agent active against Pseudomonas aeruginosa: in vitro properties.

Pipemidic acid, 8-ethyl-5,8-dihydro-5-oxo-2-(1-piperazinyl)-pyrido [2,3-d]pyrimidine-6-carboxylic acid, is a new derivative of piromidic acid. It is active against gram-negative bacteria including Pseudomonas aeruginosa as well as some gram-positive bacteria. Its potency is generally greater than that of piromidic acid and nalidixic acid. Cross-resistance is not observed between pipemidic acid and various antibiotics, and most of bacteria resistant to piromidic acid and nalidixic acid are moderately susceptible to pipemidic acid. The activity of pipemidic acid is scarcely affected by the addition of serum, sodium cholate, or change of medium pH, but is subject to the influence of inoculum size. Its action is bactericidal above minimal inhibitory concentrations.