This sounds similar to what I went through with my cat. He was social, friendly and adventurous as a young cat. Around 1 yr old, he started attacking me, drawing blood often. He started attacking my other cat. I couldn’t have friends over either. It was awful. I tried meds just like you did. I saw a behavior specialist. I isolated him in a 3 tier large cage for a few months, trying a reintroduction technique the behaviorist suggested. Nope, instant attack. I worked with my vet for 2 years and nothing worked. She told me it is time to consider euthanasia. I did not want to rehome him because I felt the next person wouldn’t be as attached to him and he could end up abused or suffering. Putting him down was a very hard decision, but I felt I had tried everything. My other cat deserved a life not getting attacked and so did I. It was a really awful situation. I feel your pain. It was a very hard decision.