Some prescriptions are the exact same drug, just different doses.
Growing up, we raised rabbits, and on occassion one would have an infection of some sort. The vet gave mom amoxicillian to give to them. Fast forward a few years, I ended up with an infection, my doctor prescribed amoxicillian. I flipped! Didn't want to take rabbit medicine! lol. Turns out, it's the same thing, just different doses.
You, for obvious reasons, don't want to try and diagnose your dog's illness on your own, for the same reason you don't want to guess as to what drug or how much to give him, as you could do serious damage to your dog's health.