Hi again Neil....I'm sorry you're spending alot of money with no results. I agree with the other posters who suggested better lights and the Oxbow critical care. It may all be related to improper lighting, but then again it may be genetic. If you haven't had him tested for adenovirus.....which is a separate test from the usual blood panel, you can find out if that may be the cause. As for starting on antibiotics, nothing should be given until a DEFINITE problem is found. So IF the vet finds a moderate -high parasite load, then the type of parasites will determine what meds. should be given. For instance, Panacur is often prescribed for pinworms, whereas Ponazuril [ Toltrazuril ] would be for coccidia. Some vets give Albon for coccidia, but it is much harsher than Ponazuril and your boy already is having a rough time.
I just want to add that a vet being affiliated with a zoo does not make them any more experienced with beardies UNLESS he deals with sick beardies on a regular basis. There was a poster here years ago who had a fat, obviously gravid female ready to lay eggs, scratching like crazy in her tank and not eating. The poster was inquiring as to what the problem could be....I suggested that it was about to lay eggs. Poster took it to the vet who was affiliated with a zoo here in the U.S, vet said " no eggs " just carry on as usual. It was pretty obvious the dragon was about to lay eggs, and sure enough did within a day of the post.
So I'm not putting the vet down, but just want you to be aware. If he has NO clear diagnosis, just nutrition and proper lighting may be all that's needed. I know you don't want to waste money, and I'm sorry your dragon is in this condition. Ask the vet for the Critical Care formula [ much better than dog food ! ] and if he doesn't carry it, look online.