Zero Order Elimination Kinetic
The Fundamental Concept
The drug follows zero-order kinetic when its elimination mechanism gets saturated.
When elimination mechanism is not saturated
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Increasing drug concentration
↓
Increases rate of drug elimination (First order)
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Eventually, the elimination mechanism gets saturated
↓ Rate of elimination reaches a maximum (End of first order)
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Further increase in drug concentration
↓
No more increase in rate of elimination (Zero order)
Properties of First-Order Elimination Kinetic.
Rate of elimination is constant irrespective of plasma concentration.
Rate of elimination is constant at the maximum level.
It no longer increases with increasing plasma concentration.
Clearance is not constant.
Plasma half-life is not constant.
Constant amount of drug is eliminated in unit time. (i.e. the maximum amount)
Plot of plasma concentration against time is linear.
Example
Very few drugs follow zero-order kinetics.
Example: Ethyl Alcohol.
The elimination mechanism gets saturated very quickly
↓
Follows zero-order kinetic at virtually all concentrations
For most of the drugs
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Elimination mechanism is not saturated within their therapeutic range of concentration
↓
Follow first-order kinetic