Some people have a very low tolerance to drugs, I take 3 10mg valium a day, and no problems. Talk to your Doc but I slowed down the last couple weeks and only take them when I start to stress. the least amount of drugs through the liver the better,(but I believe xanax is eliminated through the kidneys not the liver so is better than valium)
Maybe your liver isn't filtering it out as efficiently if you have a ton of liver damage?
I haven't ever heard of anything like this, I would think that the doctors would caution us IMMEDIATELY on something like this - if drugs were acting that way they could very well be toxic even in small amounts...but just because I haven't heard of it doesn't make it not possible.
Hope you get a "real" answer.