Re: WHY is 2^-5 used to compute max # half-lives? » Janelle

Posted by JohnX2 on April 5, 2002, at 18:27:55

In reply to WHY is 2^-5 used to compute max # half-lives?, posted by Janelle on April 5, 2002, at 18:09:50

> I've got info from two different threads that I've gotta combine here to ask my question so please bear with me. Thanks!
>
> Okay, in one thread it said that no matter what your starting concentration is, after 5 half-lives you are at 1/32 of where you started, which is *effectively* gone.
>
> Under another thread it said that after 5 half-lives there is 2^-5 = 1/32 of the original amount
> left. Where does this equation come from? Why is it used - is it an equation that some genius came up with to realize that it takes 5 half lives to effectively eliminate a drug? HELP!
The definition of a 1/2 life is that at time t+1 there is 1/2 of the medicine that there was at time t.
so for 5 , 1/2 lifes:
we have:
1/2 * 1/2 * 1/2 * 1/2 * 1/2 = 1 / (32) = 1 / ( 2 ^ 5) = 2 ^ -5
No genious. Just math.
John

Thread

Could someone explain HALF-LIFE w/ example! Janelle 4/4/02
...
GC/MS = Gas Chromatography / Mass Spectrometry » Janelle fachad 4/5/02
Re: How can 1/2 life be SAME for DIFF concentrations? » Janelle IsoM 4/5/02
Re: How can 1/2 life be SAME for DIFF concentrations? » Janelle JohnX2 4/5/02
2nd Question- It's All Relative » Janelle fachad 4/5/02
See Above Post » Janelle fachad 4/5/02
Re: FACHAD: 2 questions 4 U (1/2 lives revisited!) » Janelle Sunnely 4/5/02
ISO: thx, how do you raise to a negative number: Janelle 4/5/02
ISO: you are GREAT! But shouldn't it be AFAIc for: Janelle 4/5/02
Re: Relationship btw 1/2 life and onset of action? » Janelle Sunnely 4/5/02
No need 4 redirect, I understand! Thanks, JX2! (nm) » JohnX2 Janelle 4/5/02
ISO: Ack, I'm having trouble following that » IsoM Janelle 4/5/02
WHY is 2^-5 used to compute max # half-lives? Janelle 4/5/02
Re: WHY is 2^-5 used to compute max # half-lives? » Janelle JohnX2 4/5/02
I get the math now, but why 5, it seems arbitrary (nm) » JohnX2 Janelle 4/5/02
yes,5 is arbitrary, could just as well be 6 or 7.. (nm) » Janelle JohnX2 4/5/02
Another (easy!) question re your explanation! » JohnX2 Janelle 4/5/02
Re: Another (easy!) question - Bingo! (nm) JohnX2 4/5/02
EE-GADS! No, it can't be 6, 7, etc. because: » JohnX2 Janelle 4/5/02
Re: EE-GADS! No, it can't be 6, 7, etc. because: » Janelle JohnX2 4/5/02
1/2 LIFERS:did a famous pdoc invent the following: Janelle 4/5/02
JohnX2: how does this work in reverse: » JohnX2 Janelle 4/5/02
Re: JohnX2: how does this work in reverse: » Janelle JohnX2 4/5/02
OMG! Logarithms! EEK, forget it, but thanks! (nm) » JohnX2 Janelle 4/5/02
ISO: quests 4 U under 1/2 life and on Admin! Janelle 4/5/02
It Was Something My Pdoc Told Me » Janelle fachad 4/5/02
...
Re: Adam, I have no idea what you did! what is ''e''? 2sense 4/15/02

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