This document defines drug absorption as the movement of an unchanged drug from the site of administration into systemic circulation. It describes the main mechanisms of drug absorption as passive diffusion, carrier-mediated transport including facilitated diffusion and active transport, pore transport, and endocytosis including phagocytosis and pinocytosis. Passive diffusion is the major process for over 90% of drugs, driven by concentration gradients. Carrier-mediated transport uses carrier proteins and can involve expenditure of energy for active transport against concentration gradients. Endocytosis engulfs materials in membrane vesicles for intracellular transport. Key factors influencing absorption are drug solubility, concentration, absorbing surface area and vascularity.

1. Seminar on

2. DEFINITION
“Absorption is defined as the process of
movement of unchanged drug from the site of
administration to the systemic circulation.”

4. MECHANISM OF DRUG ABSORPTION
1) Passive diffusion and filtration
2) Specialized transport
A) Carrier- mediated transport
i) Facilitated diffusion
ii) Active transport
a) primary active transport
b) secondary active transport
3) Phagocytosis
4) Pinocytosis

5. Passive Diffusion
 It is defined as the
difference in the drug
concentration on either
side of the membrane.
 Also called nonionic
diffusion
 It is the major process for
absorption of more than
90% of the drugs.
 The driving force for
this process is the
‘concentration or
electrochemical gradient’.

6. PORE TRANSPORT
 It is also called as Convective transport, Bulk flow
or filtration.
 The driving force for this process is the
‘hydrostatic pressure or the osmotic differences
across the membrane’.
 The process is important in the absorption of low
molecular weight, low molecular size drugs.
 Example: Urea, Water, Sugar

7. CARRIER-MEDIATED TRANSPORT
 The mechanism is thought to involve a
component of the membrane called as the carrier
that binds reversibly or non-covalently with the
solute molecules to be transported.
 The carrier may be an enzyme or some other
component of the membrane.
 Two types
 Facilitated diffusion
 Active transport

8. FACILITATED DIFFUSION
 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.

9. ACTIVE TRANSPORT
 It is process where the
materials are transported
across membranes against
a concentration gradient.
 The drug is transported
from a region of lower to
one of higher concentration
i.e.. against the
concentration gradient or
‘uphill transport’.
 Examples : Sodium,
potassium, iron, glucose
and vitamins like niacin,
pyridoxine and ascorbic
acid.

10. ENDOCYTOSIS
 Also called Corpuscular or Vesicular transport
 It involves engulfing extracellular materials within a
segment of the cell membrane to form a saccule
or a vesicle which is then pinched-off
intracellularly.
 Includes two type of process:
Phagocytosis and Pinocytosis

11. PHAGOCYTIC UPTAKE OF MACROMOLECULES

12. PINOCYTOSIS
 This process is
important in the
absorption of oil
soluble vitamins &
in the uptake of
nutrients.

13.  Aqueous solubility
 Concentration
 Area of absorbing surface
 Vascularity of absorbing surface
 Route of administration

14. References
 Essentials of Medical pharmacology by K.D Tripathi
pg;no 12-17.
 www.authorstream.com
 http://www.google.co.in/images

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