Brief Answer:
10 mg a day for a week...

Detailed Answer:
Hmm....Rapid and complete stopping of a high dose of a benzodiazepine is quite dangerous. Urine screening is not generally the first consideration in this context. Withdrawal and potentially fatal seizures, hallucinations, etc. are a concern in this context.

Then.. xanax is a rapidly removed drug. Even one week is a really long time to detect it.
http://www.aafp.org/afp/2010/0301/p635.html
Charcoal, vitamins etc are unlikely to change things very much if at all. Xanax is a short acting drug mainly because it's breakdown products don't do anything and there aren't a lot of them. Consequences are it is fairly short acting with a fairly crisp on and off response, also it's metabolism isn't influenced that much. Some drugs that could interfere with it's metabolism and make it HARDER to get out of your system (grapefruit juice increasing how much drug gets in; st. johns wort decreasing how fast it is removed).. don't do much to xanax either way.

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Brief Answer:
I'm rather different than your other doctors

Detailed Answer:
I have a PhD in pharmacology and board certification in Addiction. As opposed to the other answers you've gotten I actually look up the information. I'm weird that way. It has gotten me into trouble.
http://www.ncbi.nlm.nih.gov/pubmed/0000
2-3 days.
http://www.aafp.org/afp/2010/0301/p635.html
2-3 days.
This is alprazoloam (xanax). Valium is a whole different story.

http://www.nerdpocalypse.net/alprazolam.html

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Brief Answer:
oh.. chronic abusers have significant problems....

Detailed Answer:
I note that this is not the first YEAR you've asked the identical question. Several points:
First: suddenly stopping benzodiazepines is dangerous and can cause fatal delerium tremens with hallucinations and seizures.
Second. There isn't much accumulation of xanax. This is not so true of more oily and longer lasting benzodiazepines such as valium.
Third, they tell me there is an option for directly asking a particular doctor. I haven't found that feature, so I cannot say for sure. Certainly, I will be thrilled to answer.
Fourth, this is general information and cannot say in your particular case. I happen to have (one) patient on xanax for anxiety. This is because she is a very particular case! She has a lot of anxiety. But also, she has a past of a LOT of alcoholism and a very poor liver. With this, her elimination of alprazolam is very slow (and with valium perhaps non-existant!). So... the very lowest dose of alprazolam at only twice a day covers her well. But it might show up for a little more than 3 days due to the liver issue. On the other hand, it's below the generally lowest dose, so, it might be below the test detection depending on the test. (generally used ones are NOT very sensitive).

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Brief Answer:
well... what can you do ?

Detailed Answer:
The point about alprazolam is that it is a short acting drug because it goes in and out without much modification. It's half life is a few hours. Obviously, it is a 3 time a day drug because it doesn't stay in the body long. Ok.. wouldn't hurt to drink a decent amount of water in the days leading up to the test (BUT, having a urine that is very very dilute is both an invalidated test and a red flag that someone is trying to hide something). So, not the day of the test.

Charcoal, thinking good thoughts.. not going to affect things.

Then, there's the issues about alprazolam withdrawal (which would be mostly over by day 8). Then there's the issue about addiction to benzodiazepine and.. use even when one knows it is a bad idea would be an indication of addiction.

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