I often see antibiotics like ampicillin are mixed into fluids for subcutaneous infusions when treating dogs and cats with diarrhea or fever at emergency medical care centers. I've always wondered how effective it is when antibiotics are administered just once, like the above cases. Do drug resistances come out easily from a single administration? Do they only happen after multiple administrations? I understand that emergency care has its own reasons for treatment, but I would appreciate it if you could answer my question. Thank you for your time.