What can I say, other then that I have a pretty good idea what you're going through and I know how tough it is, but also that as soon your brother realizes he needs to get his life together there is a way out.
I went through something similar with my younger brother. While it wasn't drug related perse, the combination of an anti-social personality-disorder, the medication he uses to deal with that and a drinking habit made for a particularly explosive mix that made him do things to me, my sisters, mom and dad and our property..and last but not least himself, for which there is no excuse (not even for a brother or son). It was devastating to see a handsome, truly bright and creative young lad go the hell in a handbasket. We too had to make the heart breaking decision to essentially kick him out of the house (let's face it, doing this has to be the one of the worst things for parents and brothers/sisters to have to go through), because otherwise we too would have ended up in the insane asylum or something and we just HAD to point out that he had to fend for himself and in order to get by he needed to get his act together.
It took a few long and indeed miserable years (just thinking about the family meetings where we were to decide wether we felt like having him around for the x-mas diner is but one of those odd and very sad moments that comes to my mind, it affects the very foundations upon which one's entire being is based...your direct family), but on the bright side, our point did hit home....HARD in the end. We did point out that we wanted to 'be there' for him at all times, but the initiative as far a treatment and dealing with his issues was entirely on his side at all times. And sure enough, in the end that's exactly what he did. He cleaned up his act, quit drinking all together (him sitting next to somebody having a beer and so much as smelling alcohol-breath just about makes him puke) Through therapy he learned how to deal with his his mental issues (it can't be cured, but it can be dealt with in an orderly manner) he finished his school with very nice grades indeed and got offered a job (that suits him particulary well) at the company he did his traineeship with as part of his education and found his own little house to live in. Essentially he is now able to look after himself in an orderly manner, and has been doing great for the last 3-4 years. There is still a good bit of healing to do when it comes to family ties, but again that's entirely up to him. Although seeing him being able to look after himself helps a lot for me, and not feeling upset anymore when a birthday is coming up, or inviting him over for cup of coffee and things.
Not sure if it helps or not, but all I'm trying to say is stick to YOUR guns, be strong for yourself and the rest of your family, but also be there for him if need be but be sure HE is doing what it takes and help out if need be as HE works his way through whatever it is he needs to go through. Thoughts and prayers are with you.