Cat with Blastomycosis

I found a stray cat two years ago after he got trapped in a snowstorm. He was very friendly (and completely intact) and the original owner was never located. I had him neutered and took him in myself.

Last summer, he was diagnosed with blastomycosis,a fungal disease, despite being a now indoor cat. The vet was a bit flabbergasted, needless to say. Maybe it had stayed dormant this whole time?

Anyway, he had lost a bunch of weight and gained an abscess on his side. Somehow, he had gotten it without breathing in the spores, as his lungs were totally clear of it. How a cat got it and without breathing it in are a total mystery, but he's kind of a weirdo.

Unfortunately, it's flared up again really badly. His face is covered in sores, his tail has an abscess, and his side is affected again. I think his joints are also a bit sore and he's lost a ton of weight. The vet has placed him back on his medicine, but we're unsure of his prognosis.

I've heard that Colloidal Silver is really good against fungus, and I want to give my cat the best chance he can have to beat this awful thing.

From what I understand, ionic silver is good on the skin, so placing it on the abscesses would be okay, right?

What dosage and ppm of Colloidal Silver do you recommend? I have no idea what's effective and what's not. I have some 20ppm on hand that my grandpa gave me, but I don't know how much to give or if that's an effective ppm.

Has anyone else faced this problem?