Plasma half life

plasma-half-life

Definition(Plasma half life):The time by which a measure will come to half is called the half of that measure.Which the measure may be conc of a drug that is called plasma half life(t ½) or may be the effect of a drug that is called biological effect half life or may be the excertion of a drug that called elimination half life.

Types of half life:

  1. Plasma t ½:The time by which conc of a drug will come to half is called the half of conc of a drug.
  2. Biological t ½ :The time by which the effect of a drug will come to half is called the biological half life of that drug.
  3. Elimination t ½:The time by which the excretion of a drug will come to half is called elimination half life of that drug.

Factros that can affecting half life:

  1. Route of administration.(oral/subcutaneous=More plasma t ½ )
  2. Plasma protien binding of a drug.(↑ PP binding=t ½ ↑)
  3. Tissue binding of a drug.(↑ tissue binding=t ½ ↑)
  4. Metabolism of a drug.(↑ Metabolism=t ½ ↓)
  5. Excretion of a drug.(↑ Excretion=t ½ ↓)
  6. Pathology in kidney,liver.(t ½ ↑)

Importance of half life:

  • Half life gives a gross idea about the pharmacokinetics & pharmacodynamics of a drug.
  • Half life gives idea about the duartion of action of a drug.
  • It can guide the dosage schedules:
  •     Low t ½ =Frequent administration.
  •     High t ½ =Should be given once or twice daily.

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