The document discusses the mechanisms of drug absorption from various routes of administration into systemic circulation. It defines absorption and describes the common routes like intravenous, oral, etc. The major mechanisms discussed are transcellular transport (passive diffusion, active transport), paracellular transport through tight junctions, and vesicular transport. Gastrointestinal absorption involves drug permeating the cell membrane via these mechanisms, with passive diffusion being common for lipophilic drugs of low molecular weight. The conclusion emphasizes the importance of understanding these mechanisms for drug design and selection of administration routes.

1. MECHANISM OF DRUG
ABSORPTION.
Presented by:
Lohiya Waqar A.
DEPARTMENT OF PHARMACEUTICS,
R.C.P.I.P.E.R,
SHIRPUR.
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2. CONTENT:
 INTRODUCTION.
 DEFINITIONS.
 COMMON ROUTS OF DRUG ABSORPTION.
 GASTROINTATINAL ABSORPTION OF DRUG.
 MECHANISMS OF DRUG ABSORPTION.
 CONCLUSION.
 REFRENCES.
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3. INTRODUCTION.
PHARMACOKINETICS :
Pharmacokinetics is the science of the kinetics of drug absorption,
distribution, and elimination (i.e., excretion and metabolism).
PHARMACODYNAMICS :
Pharmacodynamics refers to the relationship between the drug
concentration at the site of action (receptor) and pharmacological
response.
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4. ABSORPTION :
It is defined as the process of movement of unchanged
drug from the site of administration to the systemic circulation.
There always exist a correlation between plasma concentration
of a drug & the therapeutic response & thus, absorption can also be defined as
the process of movement of unchanged drug from the site of administration to
the site of measurement. i.e. plasma.
DEFINITION
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5. BIOAVAILABILITY/ABSORPTION OF DRUG
FROM COMMON ROUTES OF DRUG
ADMINISRATION.
 PARENTERAL
 INTRAVENOUS(IV)
 INTRAMUSCULAR INJECTION(IM)
 SUBCUTANEOUS INJECTION(SC)
 ENTERAL ROUTES.
 BUCCAL/SUBLINGUAL(SL)
 ORAL(PO)
 RECTAL(PR)
 OTHER ROUTES
 TRANSDERMAL.
 INHALATION.
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6. GASTRO INTESTINAL ABSORPTION OF DRUG.
CELL MEMBRANE:STRUCTURE AND PHYSIOLOGY.
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7. Cell membranes are generally thin, approximately 70 to 100 Å in
thickness.
The plasma membrane to be composed of two layers of phospholipids
between two surface layers of proteins, with the hydrophilic "head"
groups of the phospholipids facing the protein layers and the hydrophobic
"tail" groups of the phospholipids aligned in the interior
Lipid-soluble drugs tend to penetrate cell membranes more easily than
polar molecules.
Proteins provide a pathway for the selective transfer of certain polar
molecules and charged ions through the lipid barrier.
Pores of about 10 nm and 50 to 70 nm were inferred to be present in
membranes based on capillary membrane transport studies. These small
pores provide a channel through which water, ions, and dissolved solutes
such as urea may move across the membrane.
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8. MECHANISAM OF DRUG ABSORPTION
1) TRANSCELLULAR/INTRACELLULAR TRANSPORT
A. PASSIVE TRANSPORT PROCESSES
a) Passive Diffusion.
b) Pore transport.
c) Ion-Pair Transport.
d) Facilitated/Mediated Diffusion.
B. ACTIVE TRANSPORT PROCESSES.
a) PRIMARY ACTIVE TRANSPORT.
• Ion transporter.
• ABC Transporter.
b) SECONDARY ACTIVE TRANSPORT.
• Symport.
• Antiport.
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9. 2) PARACELLULAR
A. PERMIATION THROUGH TIGHT JUNCTION.
B. PERSORPTION.
3) VESICULAR /ENDOCYTOSIS.
A. PHAGOCYTOSIS.
B. PINOCYTOSIS.
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10. 1) TRANSCELLULAR/INTRACELLULAR
TRANSPORT :
 It is defined as the passage of drug across the GI
epithelium.
 It is the most common pathway for drug
transport.
A. PASSIVE TRANSPORT PROCESS:
These transport processes do not require
energy other than that Brownian motion to cross
membrane.
a) PASSIVE DIFFUSION :
Passive diffusion is the process by
which molecules spontaneously diffuse from a
region of higher concentration to a region of
lower concentration.
 This process is passive because no external
energy is expended. 10

11.  Also known as convective
transport, bulk flow or filtration.
Important in the absorption of
low molecular weight (less than
100). Low molecular size &
generally water-soluble drugs
through narrow, aqueous filled
channels or pores in the membrane
structure.
E.g. urea, water & sugars.
The driving force for the passage
of the drugs is the hydrostatic or
the osmotic pressure difference
across the membrane.
b) Pore Transport:
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12. Responsible for absorption of compounds which ionizes at all pH
values. e.g. quaternary ammonium, sulphonic acids
Ionized moieties forms neutral complexes with endogenous ions
which have both the required lipophilicity & aqueous solubility for
passive diffusion.
E.g. Propranolol, a basic drug that forms an ion pair with oleic
acid & is absorbed by this mechanism.
c) Ion-Pair Transport :
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13.  This mechanism involves the
driving force is concentration
gradient.
 In this system, no expenditure of
energy is involved (down-hill
transport), therefore the process
is not inhibited by metabolic
poisons that interfere with
energy production.
 Example: Entry of glucose into
RBCs and intestinal absorption
of vitamins B1 and B2.
d) Facilitated diffusion:
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14. B. ACTIVE TRANSPORT PROCESSES:
These transport processes require energy from ATP to move
drug molecules from extracellular to intracellular milieu.
a) PRIMARY ACTIVE TRANSPORT:
In this process,there is direct ATP requirement.Moreover,the
process transfers only one ion or molecule and in only one
direction, and hence called as uniporter .
e.g. Absorption of glucose.
Carrier proteins involved in primary active transport are of
2 types :
 Ion transporters.
 ABC transporters.
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15. ION TRNSPORTER :
 Ion transporter are responsible for transporting ions in or
out of cells.A classic example of ATP driven ion pump is
proton pump which is implicated in acidification of
intracellular compartments.
two types of ion transporters:
• Organic anion transporter:eg.PRAVASTATIN
• Organic cation transporter:eg.diphenhydramine.
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16. ABC(ATP cassette)transporter:
• ABC transporters are responsible for transporting
small foreign molecules especially out of
cells.i.e.exsorption which make them clinically
important.
• A classic example of ABCtransporter is P-
glycoprotein.
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17. b) SECONDARY ACTIVE TRANSPORT
In these processes, there is no direct requirement of
ATP i.e.it takes advantage of previously existing
concentration gradient.The energy required in transporting
an ion aids transport of another ion or molecule either in
the same direction or in the opposite direction.
• symport(co-transport)
• Antiport(counter-transport)
• Uniport.
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18. 2) PARACELLULAR/INTERCELLULAR
TRANSPORT:
It is defined as the transport of drugs through the
junctions between the GI epithelial cells. These pathway is of
minor importance in drug absorption. The two paracellular
transport mechanisms involved in drug absorption are :
A. Permeation through tight junctions of epithelial cells :
These process basically occurs through openings which
are little bigger than the aqueous pores .
eg.insulin and Cardiac glycosides.
B. Persorption :
Permeation of drug through temporary openings formed
by shedding of two neighbouring epithelial cells in to the
lumen.
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19. 3) VESICULAR OR CORPUSCULAR
TRANSPORT:
It involves engulfing extracellular
materials within a segment of the cell
membrane to form a saccule or a vesicle
(hence also called as corpuscular or
vesicular transport) which is then
pinched off intracellular.
 In endocytosis, there are three process:
A. Phagocytosis .
B. Pinocytosis.
C. Transcytosis.
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20. A. Phagocytosis (Cell eating)
Adsorptive uptake of solid particulates
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21. B. Pinocytosis (Cell drinking)
Uptake of fluid
solute.E.g. Sabine polio
vaccine (orally
administered.)
C. Transcytosis :
It is phenomenon
in which endocytosis
vesicle is transferred
from one extracellular 21

22. CONCLUSION :
 After seminar we concluded that :
 Oral route of drug administration is the most common for
systemically acting drugs and therefore,more emphasis will be
given to gastrointestinal(GI) absorption of drugs.
 By learning mechanism we able to design the dosage form and
select the routes of administration.
 Most of drugs are absorbed passive diffusion mechanism having
high lipophilicity and the mol.wt in the range 100-400.
 some drugs,water-soluble drugs of mol.wt lass than 100 is
absorbed by pore transport.
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23. CONCLUSION :
 Drugs that ionise at all pH conditions absorbed after complexing
with oppositely charged ions that are absorbed through Ion-
transport mechanism.
 In carrier mediated transport structure specific drugs with
affinity for carriers transported from specific sites.
 And in Endocytosis absorption mechanism macromolecular
nutrients and drugs as solid /droplets.
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24. REFERENCESː
1. D.M.Brahmankar And S.B.jaiswal,Textbook of
Biopharmaceutics and Pharmacokinetics A treatise,Sixth
edition,Vallabh Prakashan, Pg.No.5-24.
2. C.V.S.Subrahmanyam,Textbook of
Biopharmaceutics&Pharmacokinetics,Second
edition,Pg.No.80-149.
3. H.P.Rang And M.M.Dale Text book of Pharmacology, Sixth
Edition,Pg.No.98-102.
4. K.D.Tripathi,Textbook of pharmacology and
pharmacotherapeutics,Revised 21st
edition,Pg.No:9-14.
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