EE-GADS! No, it can't be 6, 7, etc. because: » JohnX2

Posted by Janelle on April 5, 2002, at 19:16:48

In reply to Re: WHY is 2^-5 used to compute max # half-lives? » Janelle, posted by JohnX2 on April 5, 2002, at 18:27:55

It has been stated on here numerous places that it takes FIVE half-lives to effectively eliminate a drug from the body.
How did this number of FIVE half-lives to eliminate a drug become a *given* - did someone somehow figure out that it takes 5 half-lives to eliminate a drug?
Next, using 5 as a *given*, how could you plug 6, 7 or whatever number into your example of:
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
If you did 1/2 *1/2 for 6,7,8, whatever number of times you would not get the 1/32 answer that is the amount of the drug left after 5 half-lives.
Ack, this is bugging me out!

Thread

Could someone explain HALF-LIFE w/ example! Janelle 4/4/02
...
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: different threads » Janelle Dr. Bob 4/5/02
Re: JohnX2: how does this work in reverse: Elizabeth 4/7/02
Re: WHY is 2^-5 used to compute max # half-lives? » JohnX2 2sense 4/8/02
Re: WHY is 2^-5 used to compute max # half-lives? » 2sense Elizabeth 4/10/02
Re: WHY is 2^-5 used to compute max # half-lives? » Elizabeth 2sense 4/10/02
...
Re: Adam, I have no idea what you did! what is ''e''? 2sense 4/15/02

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poster:Janelle thread:101843
URL: http://www.dr-bob.org/babble/20020402/msgs/102073.html