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Renin Angiotensin Mechanism.

General Pharmacology-5 (Excretion of Drugs)

What is Excretion of drugs:


  • Irreversible elimination of changed or unchanged drug from the body is called as excretion.

Channels of Drug Excretion:

  • Drugs after metabolism gets excreted via different organs, for sake of simplicity they are categorized as follows,
A) Renal Channel: Through Kidney.
B) Non-renal Channel: Organs other than kidney.

A) Renal Channel:

  • kidney acts as major site for drug excretion.
  • Most of metabolites and drugs which are water soluble are excreted through kidney via urine formation by glomerular filtration and tubular re absorption processes.
  • The excretion of drugs through kidneys get affected by many factors like, glomerular filtration rate, pH of urine etc.
  • More the  glomerular filtration rate more is the urine formation and hence more will be the excretion.
  • pH of urine plays very important role in excretion of drugs as acidic drugs like phenobarbitone gets readily excreted in basic urine, while basic drugs like alkaloids gets readily excreted in acidic urine.
  • This knowlege is useful to enhance drug elimination during poisonings. (In barbiturate poisoning urine is made alkaline with NaHco3 to enhance drug excretion)

B) Non-renal Channel: Organs other than kidney:

1) Lungs:
  • Lungs are also involved in drug excretion process.
  • Mostly volatile drugs like volatile anesthetics are excreted through urine.
  • e.g. Anesthetic ether.
2) Saliva: Iodides.
3) Intestine: laxatives.
4) Milk: Antibiotics, Morphine.
5) Skin: Arsenic.
6) Bile: Phenobarbitone.

Plasma Half Life of drug:

  • The time taken by drug to reduce its concentration to half is called as plasma half life of the drug.




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