Hello taken from another website although am not experianced with these matters but feel the frog requires urgent attention *QUOTED* Quite an easy fix really - I've used Melafix to treat a wide spectrum of problems, these include but are not isolated to:
Bacterial (inc eye) infections
Skin legions and ulcers
Open wounds and tags
5ml for every 10 gallon or 45lt in UK term. It is a safe and stable way to treat amphibians, both semi and aquatic and will not harm your other inhabitants. The active ingredient in Melafix is 1% 'Melaleuca' and is an all natural Aboriginal fern.
Using any known anti bacteria solution will assist MARACYN is popular and probably quicker to source, frogs are known to regenerate