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PostPosted: Tue Mar 14, 2017 10:36 am 
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I have been trying to do a lot of math and conversions. Mostly because I am bored and interested in this topic as well as curious if I will pass or not.

What is the normal cutoff level in nanograms for Xanax in preliminary drug screens? I think it is somewhere between 200 and 300 NG/ML.

Also the half life for Xanax is roughly 26.9 hours but the average is around 11.2 hours.. Meaning it will take 11 to 27 hours for half of the dosage I took to be eliminated from my body.

I take this to me that in roughly a days time I will only have .5 mg of Xanax in my system.... Another days time I will have .25 mg in my system. another days time I will have .125 mg of Xanax in my system and so on and son un cutting the dosage in half every 24 or so hours..

So by my math in 8 days time I will have roughly .00390625 Mg of Xanax in my system.

My question is ..... Is .00390625 going to be detectable in a standard Discover Multi Use 10 panel drug screen or is that amount of Xanax detectable period? It seems like such a small amount that surely it couldn't possibly be picked up by a regular drugs screen.

Keep in mind this isn't an EMIT or gas chromatography/ Immunoassay type of test where they can find out exact amounts of drugs in people's bodies.. This is a simple piss test.

If any doctors are fluent in conversions and mg I would appreciate even an estimate or opinion of this.


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PostPosted: Tue Mar 14, 2017 11:34 am 
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Hey Jordon, you really didn't need to copy and paste a new thread. Lol. You've seen how responsive we have been to your original thread, so this is probably overkill. But I will leave it in case anyone searches the topic in the future. In general, though, we usually only allow one post of the same question. No big deal, just an FYI. Btw, I like the way your parents seem to be on your side and supportive. Sound like good folks. :)

Amy

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PostPosted: Tue Mar 14, 2017 12:19 pm 
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heard that.... sorry... just didn't want this question and few statements to be lost in the other post. You can delete if you like.


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PostPosted: Tue Mar 14, 2017 6:47 pm 
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The problem with doing very precise calculations is that some of the variables are not known, and not predictable. So even with very accurate calculations there will always be a large 'fudge factor.'

The largest unknown lies in the halflife determinations. Benzos are metabolized by enzymes at the liver called 'cytochromes'. There is information about cytochromes elsewhere, the most-straightforward in my opinion on Wikipedia (the source that students are told to ignore, for some reason). If you Google 'cytochrome that metabolizes alprazolam' you will probably get started... but those enzymes vary widely based on genetics and based on other substances that increase (induce) or decrease (inhibit) their function. Some drugs are 'auto-inducers', e.g. barbiturates-- so that the more drug taken, the faster it is metabolized. The differences in cytochrome activity result in huge differences in drug detectability-- making a drug stay in the body half, or twice, as long compared to 'normal'.

Another huge variable is the concentrating effect at the bladder. The kidneys filter very large amounts of blood, called the 'GFR' or glomerular filtration rate. Liters of filtrate are produced each day, but over 90% of that filtrate is reabsorbed, leaving some molecules behind and concentrating them. Sodium and potassium are selectively reabsorbed from the filtrate to conserve them, and some drugs are 'excreted'-- i.e. added to the filtrate in larger amounts than what passively flows through the kidneys. The concentration of benzos in urine is therefor higher than the concentration in the blood-- making the 'piss test' far more sensitive than a blood test. BUT-- only a blood test tells you the concentration of the drug in the blood or brain, which is why DUI convictions rely on blood tests rather than urine tests. Urine would detect drugs more accurately, but does not say much at all about the amount in the blood that could be impairing the person.

Finally... be careful when you use 'halflife' values. Some texts will refer to 'effective half-lives'; some refer to terminal half-lives; some to 'pharmacologic half lives'. It can be difficult to know which one of those a specific text is referring to. 'Terminal half life' refers to the time for a drug to leave the body. 'Pharmacologic' or 'effective' half life refers to the time course for the EFFECT of the drug. Let's take fentanyl for an example... fentanyl is metabolized very slowly by the liver. But after an injection of fentanyl, blood and brain levels rise rapidly, and then decrease rapidly as the drug distributes into fat. The effective half life is very short-- about 10 minutes. But the elimination half life is much, much longer. The difference becomes apparent when larger doses are administered, during cardiac cases. In those cases the fat becomes saturated with fentanyl, causing the effective half life to become closer to the elimination half life. That's why patients receiving high doses of fentanyl, during heart bypass, need to be on ventilators overnight after surgery (at least that's how they did it when I was in the OR; now they tend to use shorter-acting meds and wake people more quickly).

Those are my contributions to the discussion...


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