this presentation contains basic knowledge of suspensions including flocculated, deflocculated suspensions and interfacial properties of suspended particles

1. SUSPENSIONS
 Interfacial properties of suspended particles
 Settling in suspensions
 Formulation of flocculated suspensions.
 Formulation of deflocculated suspensions.

2.  Pharmaceutical suspension is a coarse dispersion in which
insoluble solid particles are dispersed in liquid medium.
 Particles have diameters more than 0.5μ.
 Examples of suspensions:
Oral antibiotic suspensions: E.g. Crocin Syrup, Cefixime Powder for
Oral Suspension USP; Antacid suspensions (e.g. Digene, Gelucil)
Topical suspensions (cosmetic/ protective): Caladryl, Lactocalamine.
Conc. of solids in oral & topical suspensions may be 20% or more.
Parenteral Suspensions/Eye Drops: (Solid content: 0.5-30). For these
suspensions viscosity & particle size affect the ease of injection (or
eye irritation) & bioavailability.

4.  Types of suspensions
 Based on General Class
– Oral suspension
– Externally applied suspension
– Parenteral suspension
– Ophthalmic suspension
 Based on Size of Solid Particles
– Colloidal suspension (< 0.5 micron)
– Coarse suspension (> 0.5 micron)
– Nanosuspension

5.  Based on proportion of solids
 Dilute suspensions – 2 – 10% solids
E.g. Cortisone acetate suspension
Prednisolone acetate suspension
 Concentrated suspensions - > 50% solids
E.g. Zinc oxide suspension for external use
Procaine Penicillin G suspension as injection
 Based on nature & behaviour of solids (electrokinetic
phenomena)
 Flocculated suspension
 Deflocculated suspension

6. Parameter Deflocculated Flocculated
Particles exist as Separate entities Loose aggregates
Forces acting on the
particles
Repulsive Attractive
Product appearance Pleasant Non-elegant
Rate of sedimentation Slow Fast
Particles settle
Independently and
separately
As flocs
Supernatant Cloudy Clear
Sediment when
undisturbed forms
Compact cake/
clay (closely
packed)
Loosely packed
Sedimentation volume Low High
Redispersibility
Difficult, if
compact sediment
is formed
Possible
As per DLVO Primary minimum Secondary minimum

7. Deflocculated &
Flocculated suspension

8.  Properties of Suspensions
Should not settle rapidly.
Should not form a hard cake during storage. In case, a sediment
forms, it should be easily re-dispersible on simple shaking to
form uniform mixture.
 Should not be too viscous to pour freely from orifice of bottle
or flow through syringe needle.
For external lotions, the suspension should be fluid enough to
spread easily over the affected area & not mobile that it runs off
the surface. The lotion must dry quickly & provide an elastic
protective film that should not get rubbed off easily.
These qualities are affected by properties like particle size
distribution, specific surface area, prevention of crystal growth,
polymorphic form of drug.

9. Interfacial properties of suspended particles
 For suspensions efforts are required so that particles continue
to remain dispersed/ suspended in the dispersion medium.
 When drug particles are milled, reduction in their particle size
increases surface free energy. Increase in surface free energy
makes the system thermodynamically unstable.
 Hence particles are highly energetic and tend to regroup in
such a way to decrease the total area and reduce the surface
free energy.
 Thus, these particles in a liquid system, tend to flocculate &
form light, fluffy conglomerates held together by van der
Waals forces.
 Under certain conditions, particles may adhere by strong
forces to irreversibly form aggregates which results into
caking.
 Caking occurs by growth & fusing together of crystals in the

10.  Formation of either floccules/aggregates is basically tendency
of system to attain thermodynamic stability.
 Increase in work ‘W’ or surface free energy (ΔG) brought
about by decreasing particle size results in increase in surface
area (ΔA) and is given by:
ΔG = γSL . ΔA
Where, γSL = interfacial tension between liquid medium & solid
particles.
 Thus to obtain stable state, system tends to reduce the surface
free energy & equilibrium is reached when ΔG = 0.
 Decrease in interfacial tension & surface area results in
decrease in energy.
 Interfacial tension can be reduced by addition of surfactant,
but cannot be made to zero.

11.  Presence of forces at the surface of particle affect flocculation/
agglomeration in a suspension.
 Attractive forces are London-van der Waals type; repulsive forces
are due to electrical double layer (zeta potential) around each
particle.
 In suspensions where the repulsion energy is high, collision of
particles is opposed and system remains deflocculated wherein
individual particles remain separated. They sediment slowly.
 However this phenomenon is also not desirable because such
particles when they sediment, their repulsion energy is
overcome/nullified by forming a closely-packed arrangement with
smaller particles filling the voids between larger ones. Those
particles lowest in the sediment are gradually pressed together by the
weight of the ones above. Such suspensions form cake-type sediment
which is difficult to re-disperse.
 Whereas in flocculated suspension, energy barrier is difficult to
overcome so particles always remain separated at distance of 1000 to

13.  Electrical Double layer and Zeta potential
 Most surfaces acquire a surface electric charge when they come in
contact with aqueous surface.
 A solid charged surface when in contact with an aqueous medium
possesses positive and negative ions. The counter ions are attracted
towards the surface co-ions that ions of like charge are repelled away
from the surface.
 This results in the formation of an electrical double layer, made up of
the charged particles. The charges influence the distribution of ions
resulting in the formation of an electrical double layer, made up of the
charged surface and a neutralizing excess of counter-ions over co-ions
distributed in a diffuse manner in the aqueous medium resulting into
electric potentials.
 The zeta potential refers to the electrostatic charge on the particles,
which causes them to move in electric field towards a pole of opposite
charge.
 Its magnitude may be measured using microelectrophoresis or any
other of the electrokinetic phenomena.

15.  Settling in suspensions
 Theory of sedimentation
 Sedimentation is controlled by Stokes law which gives the
velocity of sedimentation.
Where, u = velocity (cm/sec); g = acceleration due to gravity; r =
radius of particle (cm); ρ = density of dispersed phase; ρ’ =
density of dispersion medium; n = viscosity of dispersion
medium
 If it is expressed in terms of diameter then,

16.  Forces acting on particles of suspension
 Gravity Brownian Movement
Colloidal particles
Sedimentation equilibrium: Gravity is neutralized by Brownian
movement

17.  Dilute pharmaceutical suspensions with 2g of solids per 100 mL
comply with Stoke’s law.
 In dilute suspensions particles do not interfere with each other
during settling.
 This is called as free settling. For pharmaceutical suspensions
with 5-10 % or more solids show hindered settling, particles
interfere with each other and for such, Stokes law is not
applicable.
 If particles are non-uniform & non-spherical then Stoke’s law is
modified:
u‘ = rate of fall at the interface in cm/sec
u = velocity of Sedimentation as per Stoke’s law
€ = initial porosity of the system
n = measure of hindering of system which is constant for each

18.  Stokes' equation is useful in fixing the factors in formulation
 Particle size control:
Too large or too small particles should be avoided.
Larger particles will settle faster at the bottom of the container;
particles >5µm will impart gritty texture to the product and cause
irritation when injected or instilled into the eye; particles >25µm
may block the needle.
Fine particles will easily form hard cake at the bottom of the
container.
 Viscosity of medium:
Higher viscosity will enhance physical stability; inhibit crystal
growth; prevent transformation from metastable to stable
polymorphic form.
Higher viscosity will hinder redispersibility; retard drug absorption
and lead to problems in handling.
 Density of the medium: Add materials such as polyvinyl

19.  Effect of Brownian Movement
 In case of suspensions with particles of diameter 2-5 μm
(depending on density & viscosity of dispersion medium),
Brownian movement counteracts sedimentation at room
temperature and keeps dispersed particles in random motion.
 The critical radius (r) below which particles remain in
suspension by virtue of Brownian motion (bombardment of
particles by molecules of suspending medium) has been
determined by Burton.
 When particles are suspended in 50% glycerin solution (which
has viscosity of 5 centipoise), Brownian motion is hindered.
In case of pharmaceutical suspensions, where viscosity is
much more than 5 centipoise, it is unlikely that particles show
vigorous Brownian Motion.

20.  Sedimentation of Flocculated Particles
 In case of flocculated systems, flocs (comprising of small &
big particles) tend to fall together, producing a distinct
boundary between sediment & supernatant liquid (clear).
 However in case of deflocculated suspensions where particles
of various particle sizes are separated, the situation is slightly
different. As per Stokes law, larger particles settle more
rapidly than smaller particles. Smaller particles continue to
remain suspended for a longer time. Hence no clear boundary
is formed & supernatant continues to remain turbid for longer
time.
 Initial rate of settling of flocculated particles depends on floc
size & porosity of aggregated mass. Subsidence is the term
used to describe settling of flocculated systems.

22.  Sedimentation Parameters
 Sedimentation Volume (V)/ Sedimentation Height (H)
 Degree of flocculation

23.  If the volume of sediment in a flocculated suspension =
original volume of suspension i.e. F = 1, in that case product
is said to be in flocculated equilibrium & no clear supernatant
is obtained on standing which is highly pharmaceutically
acceptable.
 It is possible to obtain F > 1 i.e. final volume of sediment >
volume of suspension. In this case, flocs that are formed are
loose and fluffy that they occupy more volume than the
suspension (F = 1.5). Extra vehicle is required to be added to
accommodate the sediment.
 Sedimentation can be studied by a more meaningful parameter

24. For a deflocculated suspension , the final sediment will be very
small. This volume is represented by
F for this sediment is given by
The degree flocculation
Degree of flocculation is more fundamental parameter than
sedimentation volume ‘F’ because it relates volume of
flocculated system to the deflocculated system.

25.  Formulation of Suspensions
 Approaches commonly used in the preparation of
physically stable suspensions fall in 2 categories:
 Use of structured vehicle to maintain deflocculated
particles in suspension.
 Using principle of flocculation where in flocs are
formed which although settle rapidly, but are easily re-
suspended with minimum agitation.

27.  Formulation additives for suspensions
 Vehicle
 Stabilizers
For physical stability: Suspending/ Thickening/ Wetting
agents/ Flocculating agents;
For chemical stability: Anti-oxidants/ Buffering agents/
Acidifiers/ Alkalizers/ Chelating agents/ Tonicity
For microbiological stability: Anti-microbial/ Anti-fungal
preservatives.
 Organoleptic additives: Sweeteners, flavorants,
Perfumes.

28. Vehicle or Solvent To provide liquid medium for suspension.
Suspending agents To suspend the dispersed particles.
Wetting agents To wet in-diffusible & poorly wettable solids (API or excipients)
in continuous liquid phase.
Flocculating agents To provide flocculation of particles in flocculated suspension.
Thickening agents To increase the viscosity of suspension.
Buffers and pH
adjusting agents
To stabilize the suspension to a desired pH range.
Tonicity adjusters To adjust osmotic pressure comparable to biological fluid.
Chelating agents To stabilize certain suspensions.
Preservatives To prevent microbial growth
Sweetening agents To impart desired sweetness to oral suspension.
Flavoring agents To impart desired flavour to oral suspensions.
Coloring agents To impart desired color to suspension and improve elegance.
Perfumes To impart desired odor to oral/ topical suspension.
Structured vehicle To construct structure of the final suspension.

29.  Insoluble particles in a suspension could be:
 Diffusible solids: Insoluble solids that are light and easily
dispersible & wetted by water. They mix readily with dispersion
medium, and stay dispersed long enough for an adequate dose to
be measured. After settling they re-disperse easily. E.g.
magnesium trisilicate, light magnesium carbonate, bismuth
carbonate, light kaolin.
 In-diffusible and poorly wettable solids: Insoluble solids are
not easily wetted, and some particles may form large porous
lumps in the liquid, whereas others may float on the surface.
These solids will not remain evenly distributed in the vehicle
long enough for an adequate dose to be measured. They are
prepared by including suitable wetting agent and by adding
suitable thickening agent to the vehicle, which increases the
viscosity of the vehicle and delays separation or sedimentation
of in-diffusible particles. E.g. for internal use include aspirin,
phenobarbital, sulfadimidine; and for external use calamine,

30.  Wetting of Particles
 The affinity between diffusible particles and liquid
phase is good, thus the liquid easily forms a film over
solid particles, which leads to wetting.
 While the in-diffusible particles have high interfacial
tension between particles and water; thus, air may be
entrained around the particles causing the particles to
float on the surface of the preparation and preventing
them from being readily dispersed throughout the
vehicle.
 Wetting of the particles can be encouraged by reducing
the interfacial tension between the solid and the
vehicle, so that adsorbed air is displaced from solid
surfaces by liquid.

32.  Wetting agents
 Hydrophilic colloids act by coating particles in one or more
layers. This provides hydrophilicity to the particles and facilitate
wetting.
E.g. acacia, tragacanth, alginates, guar gum can act as wetting
agents. However, care should be taken when using these agents as
they can promote deflocculation because force of attraction is
reduced (specially in flocculated suspension).
 Surfactants act by reducing the interfacial tension and thus
reducing the contact angle. Liquid now easily penetrates the
pores/ surface of particles and displaces air, thus facilitating
wetting.
Generally, intermediate HLB surfactants such as polysorbates
(tweens) and sorbitan esters (spans) are used for internal
preparations. Sodium lauryl sulphate and quillaia tincture are
used in external preparations.

33.  Suspending agents
 They increase the viscosity of the vehicle, thereby slowing down
sedimentation. Most agents can form thixotropic gels which are
semisolid on standing, but flow readily after shaking.
 Suspending agents can be divided into five broad categories:
 Natural polysaccharides: These agents possess natural variability
between batches and are prone to microbial contamination. They
are not suitable for external products as they leave a sticky feel on
the skin. E.g. tragacanth, acacia gum, starch, agar, guar gum,
carrageenan and sodium alginate.

34.  Semi-synthetic polysaccharides: These are derived from naturally
occurring polysaccharides. E.g. Methylcellulose (Cologel ®,
Celacol®), Hydroxyethylcellulose (Natrosol 250®), Sodium
carboxymethylcellulose (Carmellose sodium®), Microcrystalline
cellulose (Avicel®).
 Clays: These inorganic materials, mainly hydrated silicates are
used. E.g. bentonite and magnesium aluminium silicate
(Veegum®).
 Synthetic thickeners: These were introduced to overcome the
variable quality of natural products. E.g. Carbomer (Carboxyvinyl
polymer, Carbopol®), Colloidal silicon dioxide (Aerosil®, Cab-
o-sil®), Polyvinyl alcohol (PVA).
 Miscellaneous compounds: Gelatin used as a suspending agent

35.  Structured vehicles are pseudoplastic and plastic in
nature.
 Structured vehicles act by entrapping particles (generally
deflocculated) so that no settling occurs. However, in reality,
some degree of sedimentation takes place.
 Shear thinning property of these vehicles then facilitate the
reformation of uniform dispersion when shear is applied
(Thixotropy).

36.  Structured vehicles – Deflocculated suspension
 Improves physical stability of suspension.
 Structured vehicles are composed of hydrocolloids. E.g.
Methylcellulose, HPMC, Sodium CMC, Carbopol, Bentonite.
 They offer following advantages:
 Get hydrated well, swell to a great extent & produce high viscosity at
low concentrations.
 Act as protective colloid & stabilize charges.
 Desired conc. depends on: viscosity of vehicle, solid content, particle
size, density of solids.
 Density of structured vehicle can be increased by including ingredients
such as PVP, sugars, PEG, glycerin etc.

37.  Controlled flocculation – Flocculated suspension
 Can be achieved by using 3 materials:
1. Electrolytes: They act as flocculating agents by reducing
the electric barrier between particles. They are most
They act by • reducing zeta potential • decreasing force of
• formation of bridge between adjacent particles & linking
together in a loosely arranged structure • change pH.

38. E.g. Prepare series of bismuth subnitrate suspension containing
increased concentration of monobasic potassium phosphate.

39. Addition of monobasic potassium phosphate to bismuth subnitrate
suspension causes positive zeta potential to decrease owing to the
adsorption of negatively charged phosphate anion.
With continued addition of electrolyte, the zeta potential eventually falls
to zero & then increases in the negative direction.
At a certain positive zeta potential, maximum flocculation occurs & will
persist until zeta potential has become sufficiently negative for
deflocculation to occur once again.
The onset of flocculation coincides with the maximum sedimentation
volume determined. F remains reasonably constant while flocculation
persists, & only when the zeta potential becomes sufficiently negative to
effect re-peptization does the sedimentation volume starts to fall.
Finally, the absence of caking in the suspensions correlates with the
maximum sedimentation volume, which reflects the amount of
flocculation.
At lesser values of F, caking/ claying becomes apparent.
Another example is between sulfamerazine (-ve ) with aluminium
chloride (Al3+)

40. 2. Surfactants: Both ionic and nonionic have been used to bring
about flocculation of suspended particles.
They ac by • forming adsorbed monolayers on particle surface.
Efficacy of surfactants is dependent on charge & concentration.
3. Polymers: They are long chain compounds. They are most
effective.
They act by • adsorbing a part of their chains on particle surface
& projecting out remaining part into the medium • bridging to
promote formation of flocs • impart viscosity & provide
thixotropy • protective colloid action.

41.  Flocculation in structured vehicles
 Although controlled flocculation is capable of fulfilling desired
physical & chemical requisites of a pharmaceutical suspension,
the product may look unsightly if F-value < 1.
 Consequently, suspending agents like carboxymethyl cellulose,
carbopol 934, veegum, tragacanth, bentonite (either alone or in
combination) are added to retard sedimentation of flocs.
 It is very important to choose suitable formulation ingredients in
order to avoid incompatibility.
 For positively charged drug dispersion, anionic electrolyte
monobasic potassium phosphate is added as flocculating agent.
In addition to this system, hydrocolloid in minimal quantity may
be added. Now most of the hydrocolloids are negatively
charged, hence are compatible with anionic electrolyte.

42.  If negatively charged drug dispersion is flocculated using
cationic electrolyte (aluminum chloride), subsequent addition of
hydrocolloid may result in an incompatible product, forming
unsightly stringy mass having little or no suspending action &
itself settling rapidly.
 Under such circumstances, it becomes necessary to use a
protective colloid to change the sign on the particle from
negative to positive. This may be achieved by adding either
cationic adsorbent or protective colloid like positively charged
gelatin (below its isoelectric point). This cationic adsorbent or
gelatin forms a coat over the particle , thereby rendering the
particle (immaterial of its initial charge), positively charged.
 Now anionic electrolyte can be added to produce flocs that are
compatible & stabilized by addition of negatively charged
suspending agent.

44.  Rheologic considerations
 Principles of rheology are important as:
 Viscosity of suspension affects the settling of dispersed
 Change of flow property of suspension when the container is
(thixotropy) helps to easily pour the product from the container;
spreading qualities of the lotion when applied to affected area.
 They influence manufacturing of suspension.
 Pseudoplastic systems like
tragacanth, sodium alginate,
sodium CMC show desirable
qualities.
 While Newtonian liquid like
glycerin, has sufficient viscosity
to suspend particles, but it is too
high to pour easily and to spread
on skin. Furthermore, it shows
undesirable property of tackiness

45.  Suspending agents that are pseudoplastic & thixotropic are
most suitable, because they form gel-like consistency on
standing and sol-like consistency when shear is applied
 E.g. Bentonite, veegum and combination of bentonite: sodium
CMC.

46.  Preparation of suspensions
 Dispersion method:
 On small scale, suspension is prepared by grinding or
levigating insoluble particles in a mortar to a smooth paste
with a vehicle containing the dispersion stabilizer & gradually
adding remainder of liquid phase in which any of the soluble
components may be dissolved. Finally making up to the
desired volume.
 On large scale, dispersion of solid in liquid is accomplished
by use of ball, pebble or colloid mill. Dough mixers, pony
mixers, or similar apparatus may be employed.

47.  Precipitation methods:
 Organic solvent precipitation: Water insoluble drug is dissolved in a
water-miscible organic solvent such as methanol, ethanol, propylene
glycol or polyethylene glycol. Addition of organic phase to distilled
water under standard conditions leads to precipitation of dissolved drug.
E.g. Precipitation of Prednisolone with aqueous methanol/ aqueous
acetone.
 Factors to be considered: Effect of solvent on precipitate - Methanolic
precipitate of Prednisolone forms sesquihydrate when dried which can
be easily suspended in water while acetone precipitate of Prednisolone
forms a metastable, anhydrous, crystalline product when dried.
 Other factors: Volume ratios of aqueous-to-organic phase, rate and
method of addition of one phase to the other, temperature control,
method of drying precipitate, washing etc.
 Double decomposition method: Chemical reaction between two
compounds which exchange chemical moieties to form new compounds.
E.g. 1. Preparation of white lotion.
E.g. 2. Formation of zinc polysulfide by mixing zinc sulfate and

48.  Changing pH of the medium: Suitable for drugs having pH
dependent solubility.
 E.g. Estradiol suspensions: Estradiol is soluble in alkaline
solutions. Hence its concentrated solution is prepared and weakly
acidic solution (e.g. acetic acid) is added with proper agitation
which precipitates as estradiol.
 Insulin suspension: Insulin has an isoelectric point at pH 5 and it
precipitates between pH 6.9-7.3. In Protamine zinc insulin
suspension preparation, phosphate buffer is added to the final
container during filling. The vials contain acidified mixture of
protamine, zinc and insulin (solubilized). Addition of buffer
changes pH and precipitates insulin, forming its suspension.
 Adrenocorticotropin (ACTH)-zinc suspension: Change in pH
causes precipitation of zinc hydroxide or zinc phosphate. ACTH
gets adsorbed onto this precipitate providing a long-acting
formulation.

49.  Physical Stability of Suspensions
 Stability of suspensions may be achieved by
Electrostatic stabilization (DLVO theory –
maximum; Zeta potential)
Steric stabilization
Flocculation (DLVO theory – Secondary
Increasing viscosity

50.  Increasing the temperature of sterically stabilized suspensions
(formulated using non-ionic surfactants) can lead to
flocculation.
 Repulsion due to steric interaction depends on nature, thickness
& completeness of surfactant-adsorbed layers on the particles.
 When suspension is heated, the energy of repulsion between the
particles may be reduced owing to dehydration of
polyoxyethylene groups of the surfactant. The attractive energy
is increased & particles flocculate.
 E.g. When aluminum hydrocarbonate & magnesium hydroxide
gels are subjected to changes in temperature (i.e. freeze-thaw
cycles). During freezing process, particles overcome repulsive
barrier caused by ice formation, which forced the particles close
enough to experience strong attractive forces & form aggregates
as per DLVO theory. When ice melts, particles remain as
aggregates unless force is applied to overcome primary energy
peak. Aggregate size is inversely related to freezing rate (higher

51.  In addition to particle aggregation, particle growth is also a
destabilizing process resulting from temperature fluctuations or
Ostwald ripening during storage.
 Ostwald ripening is phenomenon observed in solid solutions/
suspensions or liquid sols/ emulsions which describes the change
of an inhomogeneous structure over time. In other words, over
time, small crystals or sol particles dissolve, and redeposit onto
larger crystals/ particles.

52.  Fluctuations in temperature can change particle size distribution
and polymorphic form of the drug, altering the absorption rate &
drug bioavailability.
 Particle growth is very important when the solubility of drug is
strongly dependent on temperature. Thus, when temperature is
raised, crystals of drug may dissolve & form supersaturated
solutions, which favour crystal growth.
 This can be prevented by adding polymers/surfactants.
 E.g. Crystal growth of Sulfathiazole is prevented by adding
polyvinyl pyrrolidone (PVP) polymer. The polymer forms a non-
condensed netlike film over the drug crystal, allowing the crystal
to grow out only through the openings of the net. The growth is
thus controlled by the pore size of polymer network at crystal
surface. Smaller the pore, higher is the supersaturation of the
solution required for crystals to grow.

53.  Pharmaceutical applications of suspensions (advantages)
1. Poorly water-soluble drugs which are required to be given
liquid DF can be designed as suspension. Specially, in case of
paediatrics, geriatrics, and patients having difficulty in
solid DF intact (s.a. tablet/ capsule).
2. Drug in suspension exhibits rate of absorption in the
Solution > Emulsion/Suspension > Capsule > uncoated Tablet >
tablet
3. To overcome instability of certain drug in aqueous solution:
 Insoluble form of drug may prolong the action by preventing
degradation in water. E.g. Oxytetracycline hydrochloride
hydrolyses rapidly) vs. its calcium salt (insoluble, stable).
 Reduce the contact time between solid drug particles and
media during storage. E.g. Ampicillin Powder for
 Drug that degrades in presence of water can be suspended in
aqueous vehicle. E.g. Tetracycline HCl in coconut oil.
4. Drugs that have unpleasant taste in their soluble form may

54. 5. Certain drugs must be present as finely divided particles to increase
surface area on administration. E.g. Magnesium carbonate and Mg
trisilicate are used to adsorb some toxins.
6. Bulky insoluble powders such as aluminium hydroxide, Magnesium
hydroxide, kaolin are better formulated as suspensions so that they are
easier to administer.
7. Suspension can be designed for topical applications: E.g. Calamine
lotion BP On application, after the evaporation of dispersion medium,
a light deposit of API will be present for improved efficacy.
8. Parenteral suspensions will provide prolonged action.
E.g. Intramuscular (i.m.)/ Subcutaneous suspensions of Protamine zinc
insulin or Procaine penicillin G.
E.g. Vaccine such as Diphtheria and Tetanus Toxoids and Acellular
Pertussis Vaccine Adsorbed, Suspension for (i.m.) injection
5. X-ray contrast media: E.g. oral and rectal administration of
propyliodone; Oral administration of barium sulphate.

55.  Disadvantages of suspensions
1. Sedimentation of solids occasionally gives false alarm about
suitability of the product.
2. Uniform and accurate dose cannot be achieved unless
packed in unit dosage forms.
3. Physical stability issues during storage such as
compaction of sediment cause problems that are difficult to
4. Drug is prone to oxidation and hydrolysis in dispersion
5. Liquid dosage forms are prone to microbial attack.
6. Being a liquid dosage forms & relatively bulky, sufficient
be taken during handling and transportation.
7. It is difficult to formulate when compared to solutions.

56. How might solid sodium carbonate be obtained from sodium carbonate solution?
a) Centrifugation
b) Filtration
c) Evaporation
d) It cannot be extracted
Question 2
What is the best description of blood?
a) Sol
b) Foam
c) Solution
d) Aerosol
Question 3
A suspension is formed from uniform particles of solid, of diameter 10 Mm, suspended in a solvent. W
a) Monodisperse and coarse
b) Monodisperse and colloidal
c) Polydisperse and coarse
d) Polydisperse and colloidal
Question 4
Which one of the following dispersions does not have liquid continuous phase?
a) Nanosuspension
b) Microemulsion
c) Gel
d) Foam
Question 5
Which one of the following systems has the smallest sized domains in its dispersed phase?
a) Nanoemulsion
b) Coarse suspension

57. Question 6
Which of the following sequences correctly describes the change in domain structure as more oil is
a) Bicontinuous, spherical, cylinder-like
b) Spherical, cylinder-like, bicontinuous
c) Spherical, bicontinuous, cylinder-like
d) Cylinder-like, spherical, bicontinuous
Question 7
Which method for the production of dispersions involves the formation of particles from materials di
a) Bottom-up
b) Top-down
c) Milling
d) High pressure homogenization
Question 8
The scattering of light by coarse and colloidal dispersed systems is known as?
a) Contrast matching
b) DLVO theory
c) Tyndall effect
d) Creaming
Question 9
Which of the following is not a mechanism for the separation of a physically unstable suspension of
a) Flocculation
b) Aggregation
c) Ostwald ripening
d) Hydrolysis
Question 10
In the DLVO theory of colloids, normal thermal motion may be sufficient to overcome the energy ba