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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

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Increasing drug concentration

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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

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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

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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

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