1. DIFFUSION PARAMETERS
PRESENTED BY :
NISHA N.
1st SEM M PHARM
DEPT.OF PHARMACEUTICS
SUBMITTED TO :
PROF.H.S.KEERTHY
DEPT.OF PHARMACEUTICS
MALLIGE COLLEGE OF
PHARMACY
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3. DEFINITION :
Diffusion is the movement of a substance from an area of high
concentration to an area of low concentration.
Diffusion happens in liquids and gases because their particles move
randomly from place to place.
The material that undergoes diffusion is known as diffusant or
permeant or penetrant.
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4. EXAMPLE :
1. When shaking salt into water, the salt dissolves and the ions move
until they are evenly distributed.
2. After placing a drop of food coloring onto a square of gelatin, the
color will spread to a lighter color throughout the block.
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5. This is given by Higuchi.
𝑄 = 𝐾 𝑻
Where, Q is the amount of drug released in time ‘t’ per unit area,
K is higuchi constant
T is time in hr.
Plot: The data obtained is to be plotted as cumulative percentage
drug release versus Square root of time.
Application: modified release pharmaceutical dosage forms,
transdermal systems and matrix tablets with water soluble drugs.
THEORY :
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6. Parameters that affect diffusion are :
1) Drug solubilization
2) Formulation factors
3) Concentration of drug at the Diffusion site
4) Surface area of Diffusion
5) Route of administration
6) Gastric emptying
7) Food
8) Intestinal motility
9) Metabolism of drug by GI tract
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7. 1) Drug solubilization – breaking drugs into smaller, more
absorbable particles .
Disintegration Deaggregation
Solid Granules Fine particles
Solution
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8. 2) Formulation factors – materials added to the drug during
processing can affect the solubilization of the drug.
a. Fillers – add bulk to the tablet
b. Disintegrators – cause tablet to break down into granules
c. Binders – hold tablet together
d. Lubricants – prevent tablet from sticking to machinery
Formulation factors - not clinically important if the drug is absorbed
effectively and may have important influence on drug Diffusion for
these drugs which are not effectively absorbed in the GI tract -
influence drug’s bioavailability
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9. 3) Concentration of drug at the Diffusion site :
Passive diffusion
Driving force – the concentration gradient.
The higher the concentration of the drug, the faster the rate of
Diffusion .
4) Surface area of Diffusion:
Larger the surface area , the faster the rate of diffusion . This is
because more particle can pass through the membrane as there is
more area , as in small intestine .
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10. 5) Route of administration
The rate of diffusion of a drug across a membrane depends on the
membrane permeability characteristics , if the membrane is a barrier to
drug passage this is known as membrane limited diffusion . Drugs are
delivered rapidly to highly perfused tissue and slowly to poorly
perfused tissue .
6) Gastric emptying :
Small intestine – primary site of drug Diffusion
Anything that delays/accelerates gastric emptying will decrease or
increase drug diffusion .
For all drugs - acidic, basic or neutral substances.
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11. 7) Food :
High fat food – delay gastric emptying – slow Diffusion
8) Intestinal motility – depends on whether the drug is completely
absorbed under normal condition.
a. Completely absorbed early upon entry into the small intestine,
increasing intestinal motility will not significantly affect Diffusion.
b. Not completely absorbed before entry into the small intestine,
increasing/decreasing intestinal motility will slow down/facilitate drug
Diffusion.
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12. 9) Metabolism of drug by GI tract
a. Drug metabolizing enzymes in the GI tract
b. Proteases in the GI tract
c. Microbes in the GI tract - metabolize certain drugs –
Drug metabolites are not usually absorbed
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