Did he test the frog to see if it had a bacterial infection? Because if it's something else like a fungal infection then antibiotics won't work. How are the frog's legs? Anything that looks like broken blood vessels?

If it is a bacterial infection, I don't know what to tell you. If the tank isn't cleaned out and disinfected the frog could get it again, but it's a little too soon for re-infection to happen. Maybe the medication is either not working or it's causing side-effects? My frog seemed to become sicker for quite a while after being treated for protozoa.