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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

Increasing drug concentration

Increases rate of drug elimination (First order)

Eventually, the elimination mechanism gets saturated

Rate of elimination reaches a maximum (End of first order)

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.


  • 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

Elimination mechanism is not saturated within their therapeutic range of concentration


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