Pharmacology - Alprazolam and half life

[bosch man]

Hi do i get this correctly

if one was to take 1mg xanax (assume the halflife on me is 8 hrs)

in 8hrs it would be 0.5mg

in 16hrs it would be 0.25mg

in 24hrs it would be 0.12mg

and so on all the time halfing until completely gone from blood stream.

If this is correct would i be right in thinking that 16 hours after taking a 1mg tab i would feel the equivilant to asthough i had just taken a 0.25tab?..and so on,if so it would explain why you should never mix with alcohol as even after 24hrs from 1mg you still have the effect of half a 0.25tab.

Correct or totally wrong?

bosch man added 3 Minutes and 29 Seconds later...

...and i assume 1 unit of alcohol clears the blood in approx 1 hour so if one drank 12 units it would take 12 hours to totally clear the system?So its half life is very short.

[Nargyle]

Half life doesn't necessarily mean the effects will still be present, plasma concentration is just as important, so even if there still is alprazolam in the system it won't necessarily be felt

[Solinari]

Basically it is correct, plasma concentrations are how it's measured and after so many hours the plasma concentration's will be half what they were originally. The half life varies from person to person due to metabolic rate and other things probably, so up to 12 hours is the half life for alprazolam.

If someone were to drink several hours after taking a single therapeutic dose of alprazolam the effects wouldn't be that prominent but it probably would have a marginal effect. The problem would come from repeated daily doses where there is a cumulative effect and one dose is skewed in to another.

As for the alcohol thing, as far as i know the half life will not be effected by the amount, so if it were the same as something like alprazolam then 12 units would take the same time to clear as 1 unit, of course drinking time would have an effect on the overall time it would take to clear. I can't find a half life for alcohol and i am not so sure it's as simple as a set amount of time, but it will take 3 half life cycles for a drug to be considered eliminated.

[Nargyle]

Setting a half life for alcohool is not that easy because while most drugs have a half-life exponential metabolism. Alcohol has a steady-state linear metabolism. Why does this happen? Well you see the structure of alcohol(ethyl) is CH3CH2OH. Now the liver breaks it down into Acetaldehyde, which is much more poisonous to the body than alcohol itself. The liver proceeds to turn it into acetic acid so the enzymes that break down alcohol may be busy with the byproducts produced by the metabolism of alcohol.

Basically since everything has to occur in a certain order before more alcohol can be broken down by the liver, the reaction is a zero order reaction.

1. Binding of the coenzyme NAD+;
2. Binding of the alcohol substrate by coordination to zinc;
3. Deprotonation of the His-51;
4. Deprotonation of nicotinamide ribose;
5. Deprotonation of Ser-48;
6. Deprotonation of the alcohol;
7. Hydride transfer from the alkoxide ion to NAD+, leading to NADH and a zinc bound aldehyde or ketone;
8. Release of the product aldehyde;
All that has to happen before the liver can break down more alcohol because acetaldehyde is poisonous so the liver has to make sure it deals with that stuff first before breaking more alcohol down otherwise you're gonna get sick.

Reputation Comments on this post:

Interesting, i had no idea

[Solinari]

I had a quick look at Wikipedia's section on alcohol in the Biological Half-life page and ended up just skimming over after the first sentence, but that was a lot easier to read and understand, i had no idea that's what happened. Is that why alcoholics end up dying unless they stop drinking because the liver can't deal with the acetaldehyde?