drug absorption,types with examples

1. DRUG ABSORPTION

2. ABSORPTION:DEFINITON
Absorption is defined as the process of
movement of unchanged drug from the site of
administration to systemic circulation.

3. ABSORPTION MECHANISM
•The main categories of drug transport
mechanisms involved in absorption are:
1. Transcellular/Intracellular transport
2. Paracellular/Intercellular transport
3. Vesicular transport

4. TRANSCELLULAR TRANSPORT
Transcellular transport is defined as
the passage of drugs across the GI
epithelium
Most common pathway for drug
transport
•Types:
•Passive transport
•Active transport

5. MECHANISM OF TRANSCELLULAR
TRANSPORT
•3 steps are involved in transcellular transport of
drugs:
i. Permeation of GI epithelial cell membrane
ii. Movement across the intracellular space(cytosol)
iii. Permeation of the lateral or basolateral
membrane

6. TYPES OF TRANSCELLULAR TRANSPORT
1.PASSIVE TRANSPORT
• These transport process do not require energy other than that of
molecular motion to pass through the lipid bilayer.
• Movement of molecules take place from higher conc to lower
conc.
• Types of passive transport:
a) Passive diffusion
b) Pore transport
c) Ion-pair transport
d) Facilitated diffusion

7. PASSIVE DIFFUSION
• It is defined as the difference in the
drug concentration on either side of
the membrane.
• Also called as non-ionic diffusion.
• Drug movement is a result of kinetic
energy of molecules.
• Eg of drugs undergoing passive
diffusion: most of the drugs

8. PORE TRANSPORT
• Pore transport involves the
transport of molecules into the cell
through the protein channels
present in the cell membrane.
• Also called as convective transport
,bulk flow or filtration.
• Eg of drugs undergoing pore
transport are : Very small
molecules (less than 100 daltons),
such as urea, water and sugars are
able to rapidly cross the cell
membrane through pores.

9. ION-PAIR TRANSPORT
• Absorption of drugs taking place by
ionizing under all PH conditions is termed
as ion-pair transport.
• The agents penetrate the membrane by
forming reversible neutral complexes with
endogenous ions of the GIT like mucin.
• Such neutral complexes have both
required lipophilicity as well as aqueous
solubility for passive diffusion. such a
phenomenan is called as ion-pair
transport.
• Eg of drugs: propranolol, a basic drug
forms an ion-pair with oleic acid and
quinine which forms ion-pair with
hexylsalicylate.

10. FACILITATED DIFFUSION
• It is a carrier mediated transport
systemthat operates down the
concentration gradient.
• It is the process of spontaneous
passive transport of molecules or
ions across a biological membrane
via specific transmembrane
integral proteins
• The drug moves along a conc
gradient.
• Eg: entry of glucose into molecules
and fat cells by GLUT4,vitaminB12

11. ACTIVE TRANSPORT
• These transport processes require
energy from ATP to move drug
molecules from extracellular to
intracellular.
• Movement of molecules take
place from lower conc to
highconc.
• Types of active transport:
• Primary transport
• Secondary transport

12. PRIMARY ACTIVE TRANSPORT
• Involves direct ATP requirement
• The process transfers only one ion or molecule and in only one
direction, hence called as uniporter.
• Carrier proteins involved are:
• Ion transporters
• ABC(ATP-binding cassette) transporters.
• Eg: muscle cells contain Ca2+ uniporters

13. SECONDARY ACTIVE TRANSPORT
• In this process there is no direct requirement of ATP.
• The transport of ion or molecule (coupled or co-transport)occurs either
in same or opposite direction.
• Types:
i. Symport (co-transport)
ii. Antiport (counter transport)

14. SYMPORT
• Involves movement of molecules
of both the molecules in the
same direction.
• Eg:
i. Na+ - glucose symporter,
H+coupled peptide transporter

15. H+ coupled peptide transporter

16. ANTIPORT
• Involves movement of molecules in
the opposite direction
• Eg: expulsion of H+ ions using the
Na+ gradient in the kidneys.

17. PARACELLULAR TRANSPORT
• Paracellular transport is defined as the transport of drugs
through the junctions between the GI epithelial cells.
• Mechanisms involved are:
1. Permeation through tight junctions of epithelial cells.
2. persorption

18. PERMEATION
• This process basically occurs
through openings which are little
bigger than the aqueous pores.
• Eg: insulin,cardiac glycosides.

19. PERSORPTION
• Persorption is the permeation of
drug through temporary
openings formed by shedding of
two neighbouring epithelial cells
into the lumen.

20. VESICULAR TRANSPORT
• It is the minor transport mechanism which involves engulfing
extracellular materials within a segment of the cell membrane to
form a vesicle.
• This is the only transport mechanism where by a drug or compound
does not have to be in an aqueous solution in order to be absorbed.
• Also called as endocytosis.

21. TYPES OF ENDOCYTOSIS:
• Endocytosis includes 2 types of processes:
1. Phagocytosis
2. Pinocytosis
• Eg :sabin polio vaccine, botulism toxin etc:

22. PHAGOCYTOSIS(CELL EATING)
•Phagocytosis is defined
as the adsorptive uptake
of solid particulates.

24. PINOCYTOSIS(CELL DRINKING)
•Pinocytosis is defined
as the uptake of fluid
solute.

25. REFERNCES:
• https://www.google.co.in/search?q=passive+transport+examples&oq=examples+of+passive
+diffusion&gs_l=psy-ab.1.0.0i71k1l4.0.0.0.28863.0.0.0.0.0.0.0.0..0.0....0...1..64.psy-
ab..0.0.0.GQfEtqudpas.
• D.M Brahmankar, biopharmaceutis and pharmacokinetics –a treatise.
• https://www.google.co.in/search?q=examples+of+drugs+undergoing+pore+transport&oq=e
xamples+of+drugs+undergoing+pore+tra&gs_l=psy-
ab.1.0.33i21k1l2j33i160k1.5707.17708.0.20585.26.26.0.0.0.0.420.7074.0j4j1j17j1.23.0..2..0.
..1.1.64.psy-ab..3.22.6869...0j0i67k1j0i22i30k1j33i22i29i30k1.nW2Te4YtO2w