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!

Thread

Could someone explain HALF-LIFE w/ example! Janelle 4/4/02
...
AFAIk/as far as I'm concerned HTH/hope that helps (nm) » Janelle IsoM 4/5/02
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
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Re: Adam, I have no idea what you did! what is ''e''? 2sense 4/15/02

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