This PPT discusses about excretion of drugs in human body.Pharmacology 2nd yr 3rd semester

1. EXCREATION
ASIYABI.M
ASSISTANT PROFESSOR
DEPARTMENT OF PHARMACOLOGY

2. DEFINITION
Excretion remove drug and their metabolite from the
body .
 Kidney are principal organs for excretion and excretion
through kidney is termed as RENAL EXCRETION.
 Non-renal excretion is the term used to describe
excretion by all other organs except the kidneys . The
other organs include lungs , biliary system,intestine,
salivary glands and sweat glands.

3. Process of excretion
 Renal excretion of dugs: Kidneys are responsible for
the excretion of nearly all drugs as well as their metabolite
to a certain extent. Water soluble, non-volatile , small
molecular size ( less than 500 daltons) agents thet undergo
slow metabolism undergo excretion via urine.
 Drug excretion via urine is determined by the following
processes namely glomerular filtration, active tubular
secretion, and active or passive tubular re –absorption.
 Rate of excretion = Rate of filtration + rate of secretion-
Rate of reabsorption

4.  Glomerular filtration: This is a process involving the
filtration of most compound irrespective of whether
they are ionise or unionised with an exception of
macromolecules ( that bounded to plasma proteins or
blood cells).
 It is a non-selective process which occurs in one
direction only. The glomerulus also behaves as a
negatively charged selective barrier which promotes
the retention of negatively charged compounds.
 Only 10% of cardiac output is filtered through the
glomeruli out of the 25% of blood/min thatreaches the
kidneys through the ranal artery.The rate of filtration is
knpwn as glomerular filtration rate.

5.  Although around 180 litres of protein and free ultra
filtrate of cells,passes through the glomeruli every day ,
yet, nearly 1.5litres only is excreated as urine.The
ramaining filtrate undergoes reabsorption from the
tubules.
 Active Tubular Secretion: This is a carrier-mediated
process. Compounds are transported in a direction
opposite to that of the concentration gradient during
active secretion by utilising energy.Two mechanisms of
active tubular secretion have been identified:

6.  a) A system that secretes organic acids or anions (eg
penicillin, salicylates, glucuronides, silfates) this system is
similar to tha one which secretes endogenous acid like uric
acid.
 b) A system that secretes organic bases or cations ( eg:
morphine, mecamylamine, hexamethonium).
 Tubular Re-absorption: This follows the process of
glomerular filtration. Tubular re-absorption can take place
either of the two ways.
 a) Active Tubular Re-absorption: High threshold endogenous
substance or nutrients like electrolytes,
glucose,vitamins,amino acids, which need to be conserved by
the body, usually active tubular re-absorption.Acive re-
absorption is shown by very few drugs eg: oxopurinol.

7.  Passive Tubular Re-absorption: Numerous exogenous
substance including drugs commonly exhibit passive
tubular re-absorption. The back diffusion or re-absorption
of water along with sodium and other inorganic ions
estabilishes the concentration gradient.
NON RENAL EXCRETION OF DRUG
i) Biliary excretion of drug-enterohepatic cycling: Bile acid is
produced by the hepatic cells present along the bile
canaliculi. The production as well as secretion of bile is an
active process.Re-absorption of nearly 90% of the
secreted bile acid in an active process.

8. ii) Pulmonary excretion: The process of simple diffusion
through the lungs ,aids in the absorption of gaseous and
volatile substance . In the same way diffusion can also help
in their excretion .Gaseous anaesthetic those are not vey
soluble in blood eg: nitrous oxide.
iii) Salivary excretion: This involve excretion of drugs through
the saliva and this process involve passive diffusion. The
ph-partition hypothesis forms the basis for the prediction
of salivary excretion of drugs. Through salivary ph ranges
from 5.8 to8.4 its mean value in human is 6.4 . Drugs that
exist in unionised forms and that are soluble in lipids at the
mean ph undergo passive salivary excretion.

9. iv) Mammary excretion: A drug that is excreted in milk can enter
to breast feedind infants and therefore, it Is significant .Drug
excretion in milk is not a passive process it depend on:
a) pH-partition behaviour
b) Molecular weight
c) Lipid solubility
d) Degree of ionisation
The Ph of milk ranges from 6.4 to 7.6 and possesses a mean pH
of 7.0 free, unionised lipid soluble drugs show passive
diffusion in the alveolar cells of the mammary gland. Since
milk bears acidic nature as compared to plasma drugs that are
weakly basic in nature show a greater concentration in milk
just like in case of saliva.

10. v) Skin excretion: pH- partition hypothesis also regulates the
excretion of drugs through skin via sweat. Drugs and their
metabolites that are passively excreted through the skin are
accountable to some extent for urticaria and dermatitis in
addition to other hypersenitivity reaction. Sweat shows the
excretion of compounds like benzoic acid, salicylic acid, alcohol
and antipyrine along with heavy metal such as lead, mercury,
and arsenic.
vi) Gastrointestinal excretion: Generally drugs are seen to be
excreted in the GIT when they have been administered
parentrally and their concentration gradient favour passive
diffusion. The process of GI excretion of drug is opposite that of
GI absorption.

11. vii) Genital excretion: Drug may also be excreted in the
reproductive tract and genital secretion.

12. THANK YOU