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1. Drug Excretion

2. At the end of this e-learning session you are able to…
A. Discuss How drug is excreted from
blood circulation?
B. Explain different factor affecting
excretion.

3. Excretion of drug
● Drug can be excreted in their unchanged form or as
metabolites by
- Kidney
- lungs
- intestine
● And to lesser extend by the
- sweat
- salivary
- and mammary glands.

4. ● More water soluble a drug or metabolites
More efficiently it is eliminated from the body.
• Renal excretion: 3 major process involve in the
excretion of drugs by the kidney
1. Glomerular filtration
2. Tubular secretion
3. Tubular reabsorption

6. ● Glomerular filtration & Tubular secretion
Remove the drug from plasma
● Tubular reabsorption
Retain drug in plasma
● The net excretion of drug depends --> therefore on
sum of total of 3 processes.

7. Glomerular filtration
● By this process drug molecules diffuse out of the
blood --> filtrating the glomeruli of the nephron -->
passes into the tubules of the kidney.
● Drug with molecular weight of 500 or less
Unimpeded diffusion of the drug

8. • Drug with mol weight of 5000-69000
partially impeded diffusion.
Result:
● All the drug which are not protein bound appear in
the glomerular filtrate.

9. ● Glomerular filtrate - 120 L / day
● But daily urine volume - 1-2 % of this
volume.

10. Q&A: Activity I
Q.1 What happens to drug blood
concentration after more Glomerular
filtration & Tubular secretion.
Q.2 How molecular weight affect rate of
glomerular filtration?
Q.3 How much is glomerular filtrate in a
day?

11. Activity II: Self learning of e-content

12. ● Factors influence renal excretion by glomerular
filtration:
1. Molecular size – small
2. Plasma protein binding– Less
3. Renal flow and volume of filtrate – More
Faster/ More is
excretion

13. Tubular secretion
● Proximal renal tubule --> actively secrete certain
drug and transporting them from the blood stream to
the tubular fluid.
● Acidic drugs eg. salicylates & penicillin.
● Basic drugs eg. Adrenaline & noradrenaline.

14. ● Many drugs which are secreted by tubules are also
filtered by the glomeruli
Having very short duration of action Eg. Penicillin

15. How to overcome short duration of action of
penicillin due to tubular secretion:
● Since tubular secretion required energy, it can be inhibited by
certain drug.
● Eg. Probenecid is often combined with penicillin
Inhibit active secretion process of penicillin
Prolonging the duration of action of penicillin

16. Tubular reabsorption
● Location: Almost throughout renal tubule.
● Reabsorption --> retained drug back into the blood.
● Similar to absorption --> from the gut wall.
● Drug molecule --> passively transported through
tubular reabsorption.

17. Enhancing the excretion of drug in case of
overdosing and poisoning
• Drug existing in the non ionized lipid soluble state
completely reabsorbed
● Weakly acidic drug e.g salicylate excreted better if
PH become alkaline and vice versa.

18. ● Acidification or alkalization of urine with drug like
ascorbic acid or sodium bicarbonate
used to hasten the excretion of drug in case of
overdosing or poisoning.

19. Biliary excretion
● Minor rout of elimination for unmetabolized drug.

20. ● Major rout of elimination for metabolites eg. Water
soluble conjugates like glucuronides.

21. Excreted in bile
Reabsorb in intestine
Excreted into Faces
Prolong the action of drug

22. Pulmonary excretion
● Important for gaseous and volatile liquid like general
anaesthetics.
● Blood stream Alveolar membrane
Expired air

23. ● Breatho-meter is often used to estimate the blood
level of alcohol which correlate with degree of
intoxication.
●

24. Excretion in sweat, saliva, milk and gastric juice
● Occur by passive diffusion of non-ionized form of
drug.
● Some are transported to suckling infant in breast
milk
Drug used by breast feeding mother should be
restricted to minimum.

25. Q&A: Activity I
Q.1 Name drug used for acidification or
alkalization of urine sample.
Q.2 What are the possibilities after drug is
excreted into bile?
Q.3 Which category of drugs are excreted
from lungs?