This document discusses pharmaceutical suspensions. It begins by defining a suspension as a coarse dispersion containing finely divided insoluble material suspended in a liquid medium. Suspensions are classified as either dilute or concentrated based on the proportion of solid, and as flocculated or deflocculated based on particle behavior. Flocculated suspensions have particles that form loose aggregates (flocs) while deflocculated suspensions have individually dispersed particles. The document outlines factors that influence particle settling such as size, shape, density, and viscosity. It provides quantitative expressions for sedimentation volume and degree of flocculation. Finally, it discusses formulation considerations for suspensions and methods for controlled flocculation using electrolytes or polymers.

1. Presented by: Miss Arti Darode
(Asst. Professor)
Nagpur College of Pharmacy
Coarse dispersion, suspensions
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2. Outlines
2
• Introduction
• Classifications
• Interfacial Properties
• Factor s influencing particle settling.
• Quantitative expression of sedimentation
and flocculation
• Formulation of suspension
• Controlled flocculation

3. Introduction
• A pharmaceutical suspension may be defined as a coarse dispersion containing finely
divided insoluble material suspended in a liquid medium.
• In this preparations, the substance distributed is referred to as the dispersed phase
(solid particles), and the vehicle is termed as continuous phase or dispersion
medium.
• Coarse dispersion 10 to 50 μm
• Fine dispersions 0.5 to 10 μm
• Particles ˂ 5 µm show Brownian movement
• They could be
• Oral suspension
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4. Introduction cont.
Why suspensions?
• Applications:
• Stability : Certain drugs are chemically unstable in solution but stable when
suspended.
• Easy to administered :Ease of swallowing liquids
• To mask the taste of bitter drug: The disadvantage of a disagreeable taste of
certain drugs in solution form is overcome.
• Prolong effect : Suspensions offer a way to provide sustained release effect.
• Bioavilability: Higher rate of Bioavilability as compare to other.
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5. Desirable Properties of Suspensions
2. No rapid settling of
suspended particles
3.If the particles do settle,
they must not form a hard
cake at the bottom of the
container & should be easily
re-dispersible into uniform
mixture when shaken.
4.suspension should
be easily pourable.
5.Parenteral preparations: it
should flow through the
syringe needle.
6.External preparations:
spread easily on the
surface of the skin &
imust not be too fluid to
run off the skin surface
1.The color & odor should be
acceptable and pleasing for
oral & external uses.
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6. Introduction cont….
• Sediment of solid gives false alarm of suitability of drug
• Dose precision can’t achieve (potent drug should not give)
• Physical stability ,sedimentation ,& compaction causes problem
• Liable to undergo oxidation & hydrolysis
Limitations / Disadvantages
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7. Outlines
7
• Introduction
• Classifications
• Interfacial Properties
• Factor s influencing particle settling.
• Quantitative expression of sedimentation
and flocculation
• Formulation of suspension
• Controlled flocculation

8. Classification
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• Based on proportion of solid ,suspension is classified as dilute or concentrated
• Concentrated suspension contains 50%w/v solid
• Dilute suspension contains 2-10 %w/v solid
• Depending on nature & behavior of solids suspension is classified as
flocculated & deflocculated suspension

9. Flocculation and Deflocculation in suspensions
The overall (or resultant) charge existing on the
suspended particle is called as zeta potential and
it is a measurable indication of the charge.
Therefore, flocculation and deflocculation
may be considered in terms of zeta potential.
When the zeta potential is high, the particles
remain dispersed and are said to be
deflocculated.
These particles resist collision due to the high
zeta potential even if the particles are
brought close by way of random motion or
agitation.
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10. The zeta potential can be progressively lowered by the
addition of an electrolyte (whose ion which is oppositely
charged to that of the suspended particles is preferentially
adsorbed).
At some concentration of the electrolyte, the forces of
attraction dominate over the electrical forces of repulsion
slightly.
Under these conditions (i.e. when the zeta potential is
sufficiently lowered), the particles when they approach each
other, form loose aggregates commonly called flocs.
Then such a suspension is said to be flocculated.*
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Flocculation

11. Flocculated & Deflocculated Suspensions
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12. Flocculated Suspension Deflocculated Suspension
• Particles form light fluffy conglomerates called The particles in the suspension remain
flocs. individually.
• Since the flocs are groups of particles, rate of
sedimentation is fast.
Since the particles are small and remain
separately, the rate of sedimentation is slow.
• Formation of sediment is
quick.
Formation of sediment at the bottom of the
container takes a long time.
• The sediment is loosely packed and presents a
scaffold like structure with entrapped liquid. The
sediment does not form a dense hard cake.
The sediment formed becomes eventually a
hard cake.
• Sediment volume is high. Sediment volume is small.
• The supernatant liquid becomes clear at a
shorter time since small particles are entrapped
within the floes and settle along with floes
rapidly.
The supernatant liquid remains cloudy for a longer
time as very small particles approaching colloidal
dimensions) take very long time to settle.
• Redistribution of the sedimented particles by Redistribution of the sedimented particles by
shaking the container is easy. shaking the container is difficult.
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13. Fig. 17-1. Potential energy curves for particle interactions in suspension. (From A. Martin, J. Pharm.
Sci. 50, 514, 1961. With permission.)
PARTICLE - PARTICLE INTRACTION & BEHAVIOUR
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14. Outlines
14
• Introduction
• Classifications
• Interfacial properties of solid
• Factor s influencing particle settling
• Quantitative expression of sedimentation and flocculation
• Formulation of suspension
• Controlled flocculation

15. Interfacial Properties
Two factors must be taken into account, when the interfacial properties
between the solid phase and the liquid are considered:
• Surface free energy increase resulting from increase in surface area of suspended particles
due to reduction in size of particles
• Presence of electrical charges on the surface of the dispersed solid particles in a liquid
medium.
The increase in surface free energy due to a reduction in size of the particles
is given by the relation: ∆G = γ ∆’A ----------------------- (1)
Where ∆G = increase in surface free energy in ergs, ∆A = increase in surface area in cm2,
γ = interfacial tension in dynes/cm.
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16. Outlines
16
• Introduction
• Reasons for suspension
• Features desired in pharmaceutical suspension
• Classifications
• Interfacial properties of solid
• Factor s influencing particle settling
• Quantitative expression of sedimentation and flocculation
• Formulation of suspension
• Controlled flocculation

17. • Particle shape:
• Determines packing arrangement & settling behavior.
• Also affect resuspendability & stability.
• Symmetrical barrel shape particle(CaCo3) found stable suspension.
• Asymmetrical needle shape particle found stable suspension.
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18. • Brownian movement
When the size of the dispersed particles approach that of
colloidal dimensions, Brownian motion sets in. Such a
Brownian motion may be observed if the size of the
particle is reduced approximately to 2µ.
However the Brownian movement depends on the density
of the particles and the density and viscosity of the
dispersion medium.
Considering the size of the particles normally found in
most of the pharmaceutical suspensions it is unlikely that
the particles will undergo Brownian movement.
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19. •
19
• SEDIMENTATION
(THEORY OF SEDIMENTAION)

20. Stoke’s law is applicable to dilute suspensions containing
spherical particles and the settling of particles should be slow with
less turbulence i.e. the settling should be streamline.
Pharmaceutical suspensions being concentrated, there is
disturbance for the settling of particles and hence Stoke’s law
cannot be effectively applied.
However, these factors may be expected to influence the rate of
settling.
According to Stoke’s law, settling rate for the particles may be
reduced by decreasing the particle size provided the particles are
deflocculated.
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21.  Size of particle:
• Particle size reduce half of its original size, the rate of sedimentation decreases
• Reducing particle size to extreme aggregation will occur due to increase in surface free
energy
• Further fine particle have tendency to form compact cake on storage.
• Settling of particle require plenty of time to pack tightly by falling one another to form
cake.
 Density of medium
• Density of solid generally 1.5-2g/cm3
• a/c to equation if density of medium is equal to density of solid so rate of sedimentation will
zero
• Therefore there is need to increase in density of medium so difference in density will
minimize
• Density can increase by adding verious thickning agent like PVP , PVC, Sugars, Glycerin
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22. The rate of sedimentation may be delayed by increasing the viscosity of the medium (by
adding suitable suspending agents) as it is inversely related to the viscosity of the dispersion
medium.
This approach to reduce the rate of sedimentation is frequently used. However there
is an optimum level for this approach as too much increase in viscosity may hinder the
flow of the suspension out of the container.
That is, pourability is affected and the viscosity increase may also make the
redistribution of the particles uniformly throughout the dispersion medium difficult.
The other approach that may be applied is to narrow down the density difference
between the dispersed particles and the dispersion medium.
This is seldom possible as the density of solid particles is always greater than the liquid.
 Viscosity
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23. 23

24. Quantitative expressions of sedimentation and flocculation {physical stability}
Sedimentation Volume F The sedimentation volume, F, is the ratio of the equilibrium
volume of the sediment, Vu, to the total volume of the suspension, V0.
• F = Vu / V0
• F is normally ranges from nearly 0 to 1.
• When F = 1,
• No sediment is apparent even though the system is flocculated.
• Caking also will be absent.
• The suspension is esthetically pleasing, there being no visible,
clear supernatant
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25. Quantitative expressions of sedimentation and flocculation
Degree of flocculation β
• β =
𝐹𝑓𝑙𝑜𝑐
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𝐹𝑑𝑒𝑓𝑙𝑜𝑐
• Is a parameter for comparing flocculated systems

26. What have you learnt?
• What are pharmaceutical suspensions? What are the roles of suspensions as a dosage
form?
• Classify of suspensions
• What are the differences between flocculated and deflocculated suspensions?
• What is the degree of flocculation?
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27. Effect of viscosity
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• The traditional approach was to raise the viscosity of the dispersion medium to the
point at which sedimentation is very low.
• It would be difficult to remove a dose from the container
• It decreased the rate of sedimentation, but it is impossible to halt
sedimentation.
• Difficult to redisperse the sediment.

28. Outlines
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• Introduction
• Reasons for suspension
• Features desired in pharmaceutical suspension
• Classifications
• Physical features of the dispersed phase
• Flocculation and deflocculation
• Quantitative expression of sedimentation and flocculation
• Formulation of suspension
• Controlled flocculation

29. Formulation of suspension
• Like alcohol , glycerin, SLS
and Tween
• Minimum amount should
be used
• They are aqueous solution
of polymer
• Usually negatively charged
in aqueous media
• E.g MC, CMC, bentonite
and carbomer
• Non-Newtonian materials
of this type are preferred
over Newtonian
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30. Outlines
4/17/2017 Pharmaceutical Compounding, Dr. rer. nat. Rebaz Ali 30
• Introduction
• Reasons for suspension
• Features desired in pharmaceutical suspension
• Classifications
• Physical features of the dispersed phase
• Flocculation and deflocculation
• Quantitative expression of sedimentation and flocculation
• Formulation of suspension
• Controlled flocculation

31. Controlled flocculation
1. Electrolytes
• They are the most widely used flocculating agents.
• They act by reducing the electrical forces
of repulsion between particles, thereby
allowing the particles to form the loose
flocs.
• Example like addition of AlCl3 into
sulfamerazine in water which has negative
charge.
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32. Controlled flocculation cont.
2. Polymers
• Many polymers contain polar
functional groups that are separated
by a hydrocarbon backbone.
• A polymer molecule may adsorb to
particle surfaces while maintaining a
degree of interaction with the
solvent.
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