SpeaksSoftly
Forum Senior
Topics: 16
Posts: 190
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I am having trouble understanding how to determine how many half lifes it takes to get to a theraputic level in drugs. Any good links or someone who can explain it like you're talking to a 3 year old?
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| hitesh
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Topics: 64
Posts: 1,084
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Alright lets see this step by step.. At each step, that is after exactly one half life each time, We'll administer the same amount of drug (say 'x'). And at each step, we'll see how much of the drug is left in the body.
0.time= 0 .. x amount of drug given
1. After 1 half life... drug left = 50% of x.... Give another shot of x amount.
2. 2 Half lives : Drug left : 25% of x (50% of 50% of x) PLUS 50% of x (that was given at step 1) === 75% of x.... Give another shot of x
3. 3 half Lives: Drug left== 37.5% of x ( 50% of 75% of x) PLUS 50% of x ( that was given in step 2) ==== 87.5% of x... Give another shot of x
4. 4 Half Lives : Drug left == 43.75% of x PLUS 50% of x == 93.75%.. Give another shot of x
5. 5 half lives : drug left === 46.875% PLUS 50% == 97% of x.. Give another shot of x
6. 6 half lives : drug left == 50% (approx. it's actually 48.5%) PLUS 50% = 100% of x (approx.)
Now each time you give a shot of x, you'll have abt 100% of the dose left in the plasma.. This is a steady state which, you can see, was reached only after 4-5 half lives..
Hope this makes sense.. Good Luck!
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13/30
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| usmlekiller
Forum Guru
Topics: 18
Posts: 1,010
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nicely explained!!
hitesh did u end up taking nbme 5 or 6?
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FUTURE 99ER
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| SpeaksSoftly
Forum Senior
Topics: 16
Posts: 190
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Awesome, thank you so much!!!!
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| hitesh
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Topics: 64
Posts: 1,084
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Thank you..
Usmlekiller: I will be taking NBME 5 tomorow, ... hopefully
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13/30
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