The majority of antibiotics I use in daily veterinary practice are human-origin. However, the main decision on WHICH antibiotic to use is indicated by things like location of infection, probable origin and presumptive ID of the pathogen, penetrating ability of an antibiotic molecule into a disease lesion, and stuff like that.
My favorite example is using an antibiotic that is effective for gram negative pathogens commonly found in the mouth... and using it on the skin of a dog. Because the dog has been licking the lesion... and the majority of bugs in the wound are oral in origin. I love that example
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