Dihydrostreptomycin or streptomycin in combination with penicillin G in dairy cattle therapeutics: a review and re-analysis of published data. Part 2: resistance and residues

Combination formulations of penicillin G salts and dihydrostreptomycin were developed during the 1960s and are currently marketed in New Zealand for parenteral and intramammary use in dairy cattle. In this paper, the second part of a two paper series, the mechanisms by which bacteria develop resistance to each of these drugs independently is reviewed and the impact of this resistance on potential for synergy is discussed. Further, the considerable potential for tissue drug residues with dihydrostreptomycin or streptomycin from these formulations is examined by re-analysis of literature data, demonstrating an urgent need to reassess the place for aminoglycoside-containing formulations in dairy cattle therapeutics.