Absorption and mechansim of drug absorption was described

1. ABSORPTION
ASIYABI.M
ASSISTANT PROFFESSOR
DEPARTMENT OF PHARMACOLOGY

2. DEFINITION
Entry of drug molecules into systemic
circulation from the site of application
or administration is called as
absorption.
Bioavailability: Is defined as the extent of
absorption of the drug, availability of
drug at receptor sites, and the
therapeutic effectivness of the
preparation.

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

5. PASSIVE DIFFUSION
 Drug diffuse across the membrane in
the direction of its concentration
gradient ,
from the region of higher
concentration to that of lower
concentration.

6.  No carrier molecules are required for
the transportation of drug by passive
diffusion.
 Energy is not required for absorption
of drug by passive diffusion
 It is slow process compared to other
mechanism.
 Majority of drug are absorbed by
passive diffusion .Non ionised and
lipid soluble drug diffuses quickly.

7.  Passive diffusion is best expressed by
Ficks first law of diffusion which states
that the drug molecules diffuse from a
region of higher concentration to one of
lower concentration until equilibrium is
attained and the rate of diffusion is
directly proportional to the
concentration gradient across
membrane.

8. FILTRATION
Filtration is also known as pore
transport or connective transport.
 This method is useful in the
absorption of particle of low molecular
size, low molecular weight and usually
for water soluble drug through
narrow,aqueous filled channels or in
the membrane strcture. Example:
urea,water and sugar.

9. Carrier mediated transport
Faciliated diffusion:
Drug diffuse across the membrane in the
direct of its concentration gradient, from the
region of higher concentration to that of
lower
concentration.( downhill process).
Carrier molecules are required for
transportation of drug by facilitated diffusion

10. Energy is not required for
transportation of drug since drug
diffuse from higher concentration to
lower concentration.
 Facilitated diffusion is a quick
process as compared to passive
diffusion

11. ACTIVE TRANSPORT
Drug transported across the membrane
against its concentration gradient from
region of lower concentration to region
of higher concentration.( uphill
process).
Specific carrier molecule are required
for absorption of drug by the active
transport.
These career molecule bind with drug
molecule and form a reversible
complex, which then pass through the
membrane and release the drug.

12.  Energy is required for the absorption of
drug by active transport mechanism.
 Drug transport through active transport
mechanism include l-dopa, 5-flurouracil.
 Active transport divided in to two type
Primary active transport and secondry
active transport.

13. ENDOCYTOSIS