Diffusion principal in biological system(Solubility of drug Part-5)
1. IIIrd Semesester B.
pharmacy
Physical Pharmaceutics-I
Unit-I
Solubility of drugs(Part-5)
(Diffusion Principles in biological system) Presented By :
Miss. Pooja D. Bhandare
(Assistant Professor)
Kandhar College of Pharmacy, Nanded
2. DEFINATIO
N
Diffusion is defined as the process of mass transfer of individual molecule
caused by random Brownian motion and move more rapidly from region of
higher concentration to region to lower concentration.
3. •In pharmacy, diffusion of drugs through a barrier is important.
•This barrier may be synthetic (polymeric) or natural membrane.
•The term barrier is applied to the region or regions that offer resistance
to the passage of materials.
•The material that undergoes the transport is known as diffusant or
permeant or penetrant.
•The material transport across the film may be by passive or facilitated
diffusion.
4. APPLICATION
1. The release of drug from dosage form is diffusion controlled. Such dosage
forms are available in the market as sustained and controlled release
product.
2. Molecular weight of polymers can be estimated from diffusion process.
3. The transport of drug (absorption) from gastrointestinal tract, skin, etc. can
be understood and predicted from the principles of diffusion.
4. The diffusion of drug into tissue and their execration through kidney can be
anticipated through diffusion studies.
5. 5. The process such as dialysis, microfiltration, ultrafiltration (in
the purification of colloids), haemodialysis, osmosis etc use the
principle of diffusion.
6. The experiments can be used as in vitro models for drug protein
binding studies
6. Diffusion of drug across gastrointestinal tract
oMost of the drugs, when administered orally, have to pass through GI barrier to
gain entry into the body.
oThe structure and nature of GI barrier decide the transport of drugs.
oIn general, GI barrier is highly complex structure composed of lipids, proteins,
lipoproteins and polysaccharides
oLargely this barrier is lipoidal in nature, though water pores and carrier system
are present in the membrane.
7.
8. The transport mechanism are classified as
1. Passive diffusion
2. Active transport
3. Facilitated diffusion
4. Pinocytosis
A number of drugs are absorbed by passive diffusion mechanism. This
process involves the transfer of a compound from aqueous phase through
membrane into blood.
In this case membrane act as simple barrier.
The mechanism of membrane penetration may be described by Fick’s first
law
9. Fick’s first law
−𝑑𝑚
𝑑𝑇
=
𝐷𝑃𝑆
ℎ
(Cm-Cs)
where
-dm/dt= Amount of drug diffusion per unit time
D= Diffusion coefficient of drug
P= Partition coefficient of the drug
S= Membrane surface area
h= membrane thickness
Cm= Concentration in mucosal side
Cs= Concentration in serosal side
Mucosal
side
Serosal
Side
10. DIFFUSION
Passive diffusion involves the transport of drug from a region of higher
concentration to region of lower concentration , i.e follows a concentration
gradient.
The GI barrier is lipoidal in nature and lipid soluble drugs get easily
transported.
Aspirin, Paracetamol, Chloroquine and Morphine are a few drugs that
undergo passive transport
