Dear Ahmed,

In Zero Order Kinetics, the rate of a reaction does not depend on the substrate concentration. In other words, saturating the amount of substrate does not speed up the rate of the reaction. Linear line is obtained when plotting a graph of time (t) vs. concentration [A] in a zero order reaction; the slope of this plot is a straight line with negative slope equal negative k, the half-life of zero order reaction decrease as the concentration decrease.

The zero order kinetic rate law is as followed, where [A] is the current concentration, [A]0­ is the initial concentration, and k is the reaction constant and t is time:

[A]=[A]0­−kt    

In order to find the half life we need to isolate it on its own, and divide it by 2. We would end up with a formula as such depict how long it takes for the initial concentration to dwindle by half:

t1/2=[A]0­/2k

The t1/2 formula for a zero order reaction suggests the half-life depends on the amount of initial concentration and rate constant. 

Therefore, in order to find the value of time required for release of 50% of drug content, you should divide the initial concentration by twice the reaction rate that you get from the slope of the linear plot.

Hoping this will be helpful,

Rafik