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Pharmacy/Half life of medicines


Hi Eric,

this is a general question relating to the concept of a medicine (or the metabolite of a medicine) having a half life in the human body.

I remember the concept of half life from school days as it relates to radioactive isotopes. I'm curious as to how this concept applies to the processing of chemicals in the human body. I would have thought the body could process a fixed quantity of a chemical per day.

But If the chemical has a half life of 24 hours for example, I assume the body will only process half of what remains in the body each day. How can it be that the body can only process an increasingly smaller amount of it each day?


Hi David,
Many substances compete for the same elimination pathway. Hence th body can not eliminate all the drug at once. Also some of the medication ends up in fatty tissue and leaches out slowly then eliminated.
Thank you for using Allexperts.
Eric Brandt, B.Sc. Pharm


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Eric Brandt


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