Drug absorption after oral administration

The rate of change of the amount of the drug in the body can be expressed as:

dA

dt = k a A i - k A

Initially, the rate of drug absorption is larger than the rate of drug elimination, so the amount of the drug in the body increases.

After some time, the rate of drug elimination becomes larger than the rate of drug absorption and the amount of drug in the body decreases.

By integrating the above equation:

A =

Ai ka

ka - k ( e -kt - e -ka t)

The amount of the drug in the GIT that is going to be absorbed is the product of the bioavailability (F) and the dose (D).

A =

F D ka

ka - k ( e -kt - e -ka t)
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