8/2/2019 Disperse Systems (Suspensions)
1/27
DISPERSE SYSTEMS
SUSPENSION
8/2/2019 Disperse Systems (Suspensions)
2/27
DISPERSE SYSTEMS
The term "Disperse System" refers to asystem in which one substance (TheDispersed Phase) is distributed, in discrete
units, throughout a second substance (thecontinuous Phase or vehicle).
Each phase can exist in solid, liquid, or
gaseous state .
8/2/2019 Disperse Systems (Suspensions)
3/27
SUSPENSION
mixture of two substances, one of which isfinely divided and dispersed in the other.
Suspensions:
S-S,
L-S (OR S-L),
G-S
Colloidal suspension 1 nm to 0.5 m
Coarse suspension 1 to 100 m
SUSPENSION
8/2/2019 Disperse Systems (Suspensions)
4/27
A suspension of liquid droplets or fine solidparticles in a gas is called an aerosol.
Blood is an example of suspensions
Suspensions are useful for administeringinsoluble or poorly soluble drugs or insituations when the presence of a finelydivided form of the material in the GI tract
is required.
SUSPENSION
8/2/2019 Disperse Systems (Suspensions)
5/27
The Difference Between Solution &Suspensions
When the 2 substances totally mix it iscalled a solution.
E.g. Solute + Solvent = Solution
(sugar) + (water) = Solution
We then say sugar is soluble in water, it hasdissolved.
8/2/2019 Disperse Systems (Suspensions)
6/27
The Difference Between Solution &Suspensions
Suspensions
Sometimes when we mix substances they stayin clusters. We therefore say it is insoluble in
water. E.g. Chalk + Water = Suspension
Eventually the particles sink to the
bottom to form sediment.
8/2/2019 Disperse Systems (Suspensions)
7/27
Uses of Suspensions
To administer an insoluble compound as aliquid. To lessen the unpleasant taste of an insoluble
compound by: formulating a vehicle in which the drug is not
soluble using an insoluble form of the drug (ie. salt
form or prodrug) adsorbing the drug onto an insoluble carrier
To modify the release rate of the drug. To improve the stability by reducing the fraction
of drug in solution
SUSPENSION
8/2/2019 Disperse Systems (Suspensions)
8/27
Properties of an Ideal Suspensionare:
Uniform dispersion
Palatable
Pleasing odor and color
No grittiness
Easy to pour yet not watery
No cap-lock
Temperature insensitive
SUSPENSION
8/2/2019 Disperse Systems (Suspensions)
9/27
particles should settle slowly
formulation should allow the easy
redispersion of sedimented particles a flocculated suspension is desirable than
a deflloculated suspension
a suspension should not be too viscous toreduce the sedimentation rate
SUSPENSION
Properties of an Ideal Suspensionare:
8/2/2019 Disperse Systems (Suspensions)
10/27
Routes of Administration
Oral
Ocular
Rectal
Parenteral
Topical
SUSPENSION
8/2/2019 Disperse Systems (Suspensions)
11/27
Examples of PharmaceuticalSuspensions:
1. Antacid oral suspensions
2. Antibacterial oral suspension
3. Dry powders for oral suspension(antibiotic)
4. Analgesic oral suspension
5. Anthelmentic oral suspension
6. Anticonvulsant oral suspension
7. Antifungal oral suspension
SUSPENSION
8/2/2019 Disperse Systems (Suspensions)
12/27
Preparation
Large scale: colloid mill
: mortar and pestle small scale
witting agents: alcohol, glyrecin(hygroscopic liquids)
METHODS OF PREPARATION
(1) use of controlled flocculation .
(2) use of structured vehicle.
SUSPENSION
8/2/2019 Disperse Systems (Suspensions)
13/27
8/2/2019 Disperse Systems (Suspensions)
14/27
Packaging and Storage ofSuspensions:
1) Should be packaged in wide mouth containershaving adequate air space above the liquid.
2) Should be stored in tight containers protected
from: freezing.
excessive heat & light.
3) Label: "Shake Before Use" to ensure uniformdistribution of solid particles and thereby uniformand proper dosage.
SUSPENSION
8/2/2019 Disperse Systems (Suspensions)
15/27
FACTORS TO BE CONSIDERED
Sedimentation.
Particle size.
Nernst and zeta potential. Deflocculation and flocculation.
Electrokinetic Properties.
Density of the vehicle. Viscosity of the vehicle.
SUSPENSION
8/2/2019 Disperse Systems (Suspensions)
16/27
FACTORS TO BE CONSIDERED
F=0.5 F=1.0 F=1.5
Sediment VolumeF={volume of sediment Vu}/{original volume Vo}
Vo
Vu
Vo
Vu
SUSPENSION
8/2/2019 Disperse Systems (Suspensions)
17/27
FACTORS TO BE CONSIDERED
Sedimentation volume-
F = Vsed/Vtot
The value of F normally lies between 0 to1 for any pharmaceutical suspension.
The value of F provides a qualitive
knowledge about the physical stability ofthe suspension.
SUSPENSION
8/2/2019 Disperse Systems (Suspensions)
18/27
External Forces Acting on ParticlesGravity Brownian Movement
Sedimentationequilibrium: Gravityis neutralized byBrownian movement.
FACTORS TO BE CONSIDERED
SUSPENSION
8/2/2019 Disperse Systems (Suspensions)
19/27
SETTLING & AGGREGATION
The suspension shall form loosenetworks of flocks that settlerapidly, do not form cakes and are
easy to resuspend.
Settling and aggregation mayresult in formation of cakes
(suspension) that is difficult toresuspend or phase separation(emulsion).
flock
cake
SUSPENSION
8/2/2019 Disperse Systems (Suspensions)
20/27
FACTORS TO BE CONSIDERED
Nernst potential
The difference in electric potentialbetween the actual surface of the particleand the electroneutral region is referred to
as Nernst potential.
SUSPENSION
8/2/2019 Disperse Systems (Suspensions)
21/27
Zeta potential
Potential difference between the ions inthe tightly bound layer and theelectroneutral region, referred to as zeta
potential.
FACTORS TO BE CONSIDERED
SUSPENSION
8/2/2019 Disperse Systems (Suspensions)
22/27
Deflocculation
Deflocculation of particles is obtainedwhen the zeta potential is higher thanthe critical value and the repulsiveforces supersede the attractive forces.
These deflocculated particles when
sediment form a close packedarrangement with the smaller particlesfilling the voids between the larger ones.-SOLID HARDCAKE
FACTORS TO BE CONSIDERED
SUSPENSION
8/2/2019 Disperse Systems (Suspensions)
23/27
Flocculation When this zeta potential goes below the critical
value, the attractive forces supersede therepulsive forces and flocculation occurs.
These loosely packed particles or floccs settlefaster than the defflocculated particles becauseof their larger sizes.
But unlike deffloculated particles this sedimentof floccs does not form solid cake.
This sediment of floccs is easy to redisperse by
minute agitation.
FACTORS TO BE CONSIDERED
SUSPENSION
8/2/2019 Disperse Systems (Suspensions)
24/27
Degree of flocculation-
= Ffloc/Fdefloc
(Vsed/Vtot)floc=-------------------
(Vsed/Vtot)defloc
FACTORS TO BE CONSIDERED
SUSPENSION
8/2/2019 Disperse Systems (Suspensions)
25/27
When the total volume of both the
flocculated and the deflocculatedsuspensions are same, the degree offlocculation,
= (Vsed)floc/(Vsed)defloc
FACTORS TO BE CONSIDERED
SUSPENSION
8/2/2019 Disperse Systems (Suspensions)
26/27
THIXOTROPIC SUSPENSION
A thixotropic suspension is the onewhich is viscous during storage butloses consistency and become fluid
upon shaking. A well-formulated thixotropic
suspension would remain fluid long
enough for the easy dispense of adose but would slowly regain itsoriginal viscosity within a short
time. SUSPENSION
8/2/2019 Disperse Systems (Suspensions)
27/27