Posted by Larry Hoover on February 8, 2003, at 13:23:14
In reply to Re: Half-life - Larry Hoover and » viridis, posted by bluedog on February 8, 2003, at 12:58:00
> Here's an interesting question for you regarding the half life of diazepam. I have been driving myself crazy trying to do the maths on this one but I have been assuming a completely linear decrease in the amount of diazepam that will show up in my blood plasma levels at certain intervals.
It's not linear, it's logarithmic. The converse statement would be that as serum concentration increases, excretion increases exponentially.
(snip)
> I am confused and believe that at this rate of consumption the my blood plasma level of diazepam (or it's metabolite) will continue to accumulate and will actually increase on a daily basis.Early on, there will be a relatively large fluctuation in serum levels because the dosing is intermittent enough that excretion is quite variable. As the serum concentration increases, however, excretion rates increase exponentially, until such time as net excretion between doses equals intake dosing. At that point, you have reached what is called steady-state or equilibrium pharmacokinetics.
>My questions are as follows:-
>
> 1) Are my calculations and assumptions correct?Simply put, no.
> 2) Is it not the case that with each successive day the level of diazepam in my blood will continue to increase leading to a higher and higher level of the drug in my system with the consequence that I will find it increasingly difficult to get out of bed each morning when my alarm sounds at 7.00am?If anything, you will find your body accomodates the medication as you become accustomed to the steady-state serum concentration.
> 3) Would the levels continue to increase so that I would eventually become none functional and could the levels in theory continue to increase until I would end up with a fatal accumulation of the drug in my system? Of course if the half life is in fact closer to the 30-200 hours shown in the benzo equivalence charts then the accumulation in my system may be even more pronounced.The only effect of half-life here is how long it takes for your body to reach equilibrium conditions, which is also affected, of course, by how often and how much you take. In any case, I would expect you to reach equilibrium in no more than three days time.
>
> 4) Can you please explain this to me and clarify whether my assumptions are correct or whether in fact the blood plasma levels of diazepam in my system would actually at some point stabilise and if so at what level (in mg) would this stabilisation occur?That level would be determined by your individual excretion capacity. Given the roughly ten-fold difference in half-life measured in clinical practice, you can see that determining the equilibrium concentration for you *specifically* could only be determined by blood draw and analysis.
> My gut feeling says that my assumptions must be wrong but I simply don't know why. I hope my questions will not drive you around the twist like they have done to me. Then again you may enjoy my questions and be able to explain it all to me :):).
>
> Thanks in advance guys
> warm regards
> bluedogWell, let's hope my answers have helped. ;-)
Lar
poster:Larry Hoover
thread:139500
URL: http://www.dr-bob.org/babble/20030208/msgs/140162.html