The mathematical expressions

If you know the half life you can calculate the elimination rate constant, and vise versa, from the following relationship:

t1/2 =

0.639

k

If you know one plasma conc at any time and the half life, or the elimination rate constant.

a- you can determine the drug conc at any time after this concentration.

Cp1

Cp2

You can substitue for the values of Cp1, k and t in the following equation to calculate Cp2.

Cp2= Cp1 e-kt

b- you can calculate the time required for the drug concentration to decrease to a certain concentration.

Cp1

Cp2

t = ?

You can substitue for the values of k, Cp1 and Cp2 in the following equation to calculatet t.

Cp2= Cp1 e-kt

c- you can estimate the drug concentration at any time prior to that concentration.

Cp1

Cp2

You can substitue for the values of Cp2, k and t in the following equation to calculatet Cp1.

Cp2= Cp1 e-kt
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