Oh, Jimmy, hi! It sounds like this poor kitty has a terrible abscess. I guess you don't have anything like Animal Control where you live? Would the vet you're consulting with give you the means to trap the kitty? Then you could take it in for the vet to look at.
If flies are annoying the wound, then it surely has maggots by now. This kitty is very ill at this stage...as you have witnessed.
I really don't know if I would be trying to treat this animal on my own. Maybe someone else will have an idea.
My heart goes out to you, as it's extremely hard to watch an animal suffer. Just tears your heart out.
Ok, wait, if the aerosol you were given specifically says 'do not use on cats', then don't!
The antibiotic, well, if the cat isn't drinking much, then you won't be sure if it's getting all the antibiotic or not. It's important kitty gets ALL of it, otherwise it's useless.
What's more important, is this wound gets cleaned out. The more it gets infected, the higher the chance the infection will enter the cats bloodstream leading to sepsis.
I really commend you in trying to help this poor thing. Good luck.
I'm so sad to read this about a suffering old cat...and I do mean SUFFERING...this cat needs to be humanly euthanized ASAP, sorry I know you'd like to try and treat him but given all the circumstances and the fact he's lost so much weight rapidly, I think there's no easy fix for him by you or by a Vet....this is sad
How's it going with this cat, Jimmy? Are you still seeing it around?
Opus is absolutely right, this poor kitty is suffering terribly. The kindest thing you could do at this point, is to have it euthanized...if it hasn't passed already.