Oh my, that is a serious situation. It reminds me of a documentary about a young man who was exactly the same as you describe. By that time, a person's body is revolting hard against the poison and medical attention is required.
I hope your brother finds the strength to seek help - and if there is an option to have him admitted I'd take it. It really is a matter of life and death. He can recover, but in my opinion serious professional attention is in order.
Sending positive thoughts your way - stay close here. Many folks have either been where he is or know someone who is. Good advice and support are important for you right now.