Hi,
The only thing I can think of is what several people have suggested in the past which is asking the vet to do a culture to find out exactly which if any anti-biotics would be effective.
I don't recognize the names of the ones he used but, as I have zero vetinary or medical training that isn't really surprising. Maybe people who have heard of them can chime in. I know the one used most commonly over here is baytril.
Does your vet have any experience of reptiles?
dr del