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Plasma Half-Life



Plasma Half-Life

  • Is time taken for drug concentration to fall to half of its initial value.


Types

  • Distribution Half-Life

    • Once the drug is administered in the body, initially there is a rapid fall in its plasma concentration due to its distribution in various body tissues.

    • The plasma half-life calculated for this distribution phase is called the distribution half-life.

  • Elimination Half-Life

    • Once the body tissues are saturated, the plasma concentration of the drug falls slowly due to elimination.

    • The plasma half-life calculated for this elimination phase is called elimination half-life.

    • If not specified, the term 'half-life' generally means the elimination half-life.


Plasma Half-Live in First order vs Zero Order kinetic

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rate of elimination is directly proportional to plasma concentration

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plasma half-life remains constant



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rate of elimination is not proportional to plasma concentration

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plasma half-life is not constant

 

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