The evaluation of piromidic acid as an antibiotic in fish: an in vitro and in vivo study

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Abstract
The activity of piromidic acid (PA, 8‐ethyl‐5, 8‐dihydro‐5‐oxo‐2‐prior lidinopyrido [2,3–d] pyrimidine‐6‐carboxylic acid) against bacteria in fish was evaluated in vitro and in vivo. In vitro, PA was effective against a wide range of pathogenic bacteria stocked in this laboratory and freshly isolated from fish. PA was active against organisms showing multiple drug‐resistance and showed no cross‐resistance to chloramphenicol, tetracycline and sulfamonomethoxine. In vivo, orally administered PA was effective against experimental infections with Aeromonas hydrophila and Vibrio spp. in goldfish and eels. The efficacy of PA against these infections was equal to or higher than that of chloramphenicol, and higher than that of tetracycline. Distribution of PA in the Ash was investigated by bioassay and autoradiography. In the bioassay, orally administered PA was easily absorbed and distributed in the blood and tissues of major organs within 1 h after the administration. Peak levels were attained 2 to 4 h post dosing, and no residue was detected in the blood and tissues 48 h post dosing. The results obtained from the autoradiographic investigation in goldfish were similar to those from the bioassay. Therapeutic levels of PA were well tolerated by fish when administered with feed.