Why are only certain medications weight based?

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Why are only certain medications such as Digoxin or Vancomycin and other antibiotics weight based while others are not. Also Why is Ideal Body Weight used in a patient to determine dosing, why is their actual real weight not used. And in obese patients, why is the adjusted body weight used and not their real weight or IBW? Except the fact that the drug can deposit into fat tissue, how else can fat affect the drug in the body that leads to dosing adjustments ? I have tried to research these topics but unable to come up with a clear answer. Thanks

Originally Posted by PrePharmStu2009

Why are only certain medications such as Digoxin or Vancomycin and other antibiotics weight based while others are not. Also Why is Ideal Body Weight used in a patient to determine dosing, why is their actual real weight not used. And in obese patients, why is the adjusted body weight used and not their real weight or IBW? Except the fact that the drug can deposit into fat tissue, how else can fat affect the drug in the body that leads to dosing adjustments ? I have tried to research these topics but unable to come up with a clear answer. Thanks

Search for the topic "volume of distribution" and you should find what you are looking for.

All answers will be given in pharmacy school

It all depends on Volume of distrobution, free drug conc. vs. protien bound, bioavailability of the drug, half life of the drug, how its metabolized, what the drugs theraputic range is, etc etc etc. Its a multi-layered answer.

Are you in pharmacy school?

Because they're different. Different drugs get absorbed differently, distribute differently, are metabolized differently, have different effects on the body, are excreted differently, and therefore, are dosed differently.

Pk/pd

Originally Posted by Trankuil

It all depends on Volume of distrobution, free drug conc. vs. protien bound, bioavailability of the drug, half life of the drug, how its metabolized, what the drugs theraputic range is, etc etc etc. Its a multi-layered answer.

Um, no.

Hint: plot CL vs weight.