Pharmacology of carbadox in the pig

Abstract

An evaluation has been made of the in vitro minimal inhibitory concentrations (MIC) of carbadox against various bacterial species in relation to the carbadox levels obtained in the gastrointestinal tract and in the blood after feed medication with carbadox. Although a prophylactic efficacy against orally transmitted enteropathogenic spirochaetes and anaerobic bacilli seems warranted, no justification for the therapeutic application of carbadox was found. In fact, therapeutic dosages induced hypoaldosteronism in young pigs. A direct anabolic action of carbadox could not be reproduced in healthy young pigs fed a standard commercial feed. The widespread use of carbadox in pig husbandry constitues a selection pressure towards Escherichia coli strains with MIC values above the carbadox levels in the small intestines. Carbadox R-plasmids in E. coli strains can be transmitted to other gram-negative bacilli but not to Treponema hyodysenteriae. Prevention of swine dysentery seems now to be the only indication for administration of carbadox in the feed. A lower dosage and a shorter treatment period than those currently advised might provide a marginal safety factor while still being effective.