(Suspension 2)

A pharmaceutical suspension is a coarse dispersion of insoluble solid particles in a liquid medium. ... However, it is difficult and also impractical to impose a sharp boundary between the suspensions and the dispersions having finer particles. Suspensions are an important class of pharmaceutical dosage forms

1. Suspension 2
Md. Saiful Islam
BPharm, MPharm (PCP)
North South University
Fb Group: Pharmacy Universe

2. Flocculating Agents
•Particles in suspension that have acquired a surface
charge will tend to repel one another, resulting in the
formation of a deflocculated dispersion.
•This can be reversed by the use of flocculating agents

3. Flocculating Agents
•Agents that can be added to the medium to promote
flocculation by counteracting the effect of the protective
layer are termed as flocculating agent
•These flocculating agentsinclude-
a) Electrolytes
b) Detergents and
c) Polymers

4. Electrolytes as flocculating agents
•Electrolytes are frequently used for flocculating the
particles of suspensions to obtain a product of large
sedimentation
•Examples -bismuth subnitrate
-aluminium chloride

5. Electrolytes as flocculating agents
•Mechanism
The ions of electrolytes probably –
-Reduce the electrical barrier between the particles and
-Form a bridge, between the particles of the suspension
and the ions of the flocculating agent, by the formation of
chemical bonds

6. Electrolytes as flocculating agents
•Thus, the particles are held in a loosely arranged
structure in suspension
•Although these large aggregates settle rapidly, they yield
an open cell-like structure and are easily resuspended
by agitation

7. Electrolytes as flocculating agents
•Usuallya negativeflocculating agent is added to a
suspension of positively charged particles and vice
versa
•Flocculating agent increases the sediment volume
relative to the initial value i.e. the value of V
u / V
0 (F)

8. Electrolytes as flocculating agents
•Until the value of V
u / V
0 (F)reaches to maximum,
referred to as the noncakingzone, flocculating agent
added
•Additional flocculating agent neutralizes the charge on
particles and can eventually reverse the charge and
again yield a caked suspension

9. Detergents as flocculating agents
•Both ionic and nonionic surfactants are used as
flocculating agent
•Example –polyoxyethylated nonylphenols

10. Detergents as flocculating agents
•Mechanism
-An ionic surface active agent increases the
sedimentation volume
-Nonionic detergents are adsorbed onto suspended
particles and produces flocculated system at the
appropriate concentration

11. Polymers as Flocculating agent
•Lyophilic polymers, commonly used as suspending
agent in pharmaceutical products, also act as
flocculating agent
•These polymer molecules contain active groups spaced
along their chains
•Example-carboxymethylcellulose, bentonite etc

12. Polymers as Flocculating agent
•Mechanism
•The ends of the polymer are adsorbed on the particles
and loops of the intervening chain segments protrude
into the medium
•These ends or loops are available for bridging across to
adjacent particles and thus produce a flocculated system

13. Polymers as Flocculating agent
•A number of hydrocolloids are polyelectrolytesand
used as flocculating agents. Example –Gelatin
•Their flocculating action is dependent on the pH and the
ionic strength of the medium
•An optimum pH is observed for sedimentation

14. Polymers as Flocculating agent
In the preparation of suitable suspensions, the
suspending agent may act both as a protective colloid
to keep the settled particles from caking and as a
flocculating agentto produce the loose cell-like
structure in the liquid medium

15. Sedimentation parameters
•Two sedimentation parameters that are used as
semiquantitative measurements of flocculation in a
suspension are-
a) Sedimentation Volume and
b) Degree of Flocculation

16. Sedimentation parameters
•a) Sedimentation Volume:
•Denoted by symbol, F
•Defined as the ultimate volume of the sediment , v
u,
divided by the original volume, V
o, of the suspension
before settling;
F = V
u / V
0
The value of F may be less than 1, more than 1 or equal
to 1

17. Sedimentation parameters
•When, F = 1, the sediment is equal to the total volume of
the suspension and the product is said to be in a state of
“ flocculation equlibrium”
•Such a product is quite acceptable from a
pharmaceutical standpoint because, on standing, it
shows no sediment or clear supernatant

18. Degree of Flocculation
•Denoted by the symbol, ß
•Describes the relationship between the sedimentation
volume of the flocculated suspension, F, to the
sedimentation volume of the same suspension when
deflocculated, F
∞

19. Degree of Flocculation
•Acompletely deflocculated suspension have a relatively
small volume of sediment, V
∞
•The sedimentation volume of such suspension, F is
written thus,
F
∞= V
∞/V
0
•Thus, the ratio of F and F
∞is the degree of flocculation,ß
ß = F/ F
∞

20. Degree of Flocculation
•Putting the values of F and F
∞,
•we get,
ß = V
u/ V
∞
where,
V
u = ultimate sediment volume of flocculated
suspension
V
∞ = ultimate sediment volume of deflocculated
suspension

21. Degree of Flocculation
•If the value of ß is 1, i.e. F = F
∞ , it means that there is no
flocculation in the system
•The shape and size of the suspension particles and the
distribution of sizes can influence ß
•The temperature, the density and the viscosity of the
medium are less influential factors