suspentions-1

Question 1

dispersed system

Answer 1

 The term “Disperse System” refers to a system in which one substance (The Dispersed Phase) is
distributed, in discrete units, throughout a second substance (the continuous Phase).
 Each phase can exist in solid, liquid, or gaseous state.
 Suspensions are heterogeneous system consisting of 2 phases.

Question 2

suspensions

Answer 2

A Pharmaceutical suspension is a coarse dispersion in which internal phase/insoluble solids
(therapeutically active ingredient) is dispersed uniformly throughout the external phase with the help of
suspending agents.

OR

A coarse dispersion containing finely divided insoluble material suspended in a liquid medium or
available as dry powder to be distributed in the liquid medium when desired is known as suspension.

OR

A biphasic system containing a solid phase (dispersed medium) uniformly dispersed in a liquid phase
(dispersion medium) is called suspension.

Question 3

properties of suspentions

Answer 3

 The particles in the suspension have diameter greater than 0.1μ.
 The internal phase consists of insoluble solid particles having a size range of 0.5 to 5 microns which
is maintained uniformly throughout the suspending vehicle with aid of single or combination of
suspending agent.
 The external phase (suspending medium) is generally aqueous in some instance, may be an organic
or oily liquid for non-oral use.
 Nearly all the suspensions must be shaken Before use to ensure the uniformity of the Preparation and
proper administration of dosage form.
 A solid in liquid dispersion in which the particles are of colloidal size.

Question 4

qualities of good suspensions

Answer 4

 The dispersion of particles in the suspension must be adequate (uniform).
 The settling of the dispersed particles should be minimum.
 The particle should not form a cake on sedimentation.
 The viscosity should be such that the preparation can be easily poured.
 It should be physically and chemically stable.
 It should have resistance to microbial contamination.
 It must have smooth elegant appearance.
 The main characteristic of an ideal suspension is that it should be thixotropic i.e. becomes viscous on
standing and thin readily on shearing.

Question 5

reason for formultion of pharmaceutical suspentions

Answer 5

 If patient has a difficulty of swallowing solid dosage forms (a need for oral liquid dosage form).
 Faster rate of dissolution and oral absorption than solid dosage forms, yet slower than solutions.
 Bulky insoluble powders as kaolin or chalk are better formulated as suspensions so that they are easier
to take.
 Drugs that have very low solubility are usefully formulated as suspensions.
 Drugs that have an unpleasant taste in their soluble forms (e.g., chloramphenicol (soluble) vs.
chloramphenicol palmitate (insoluble).
 Prolongation of effect (e.g. I.M and S.C. suspensions).
 Stability and instability issues:
o Insoluble forms of drugs may prolong the action of a drug by preventing rapid degradation of
the drug in the presence of water (e.g., Oxytetracycline hydrochloride (soluble, hydrolyses
rapidly) vs oxytetracycline calcium salt (insoluble, stable).

Question 6

some pharmaceutiacal suspensions

Answer 6

 Antacid oral suspensions
 Antibacterial oral suspension
 Dry powders for oral suspension (antibiotic)
 Analgesic oral suspension
 Anthelmentic oral suspension
 Anticonvulsant oral suspension
 Antifungal oral suspension

Question 7

classification based on general classes

Answer 7

A. Based On General Classes
 Oral suspension
o eg: Paracetamol suspension, antacids, Tetracycline HCl.
 Externally applied suspension
o eg :Calamine lotion.
 Parenteral suspension
o eg: Procaine penicillin G, Insulin Zinc Suspension

Question 8

based on proportion of solid particles

Answer 8

 Dilute suspension (2 to10%w/v solid)
o Eg: cortisone acetate, predinisolone acetate
 Concentrated suspension (50%w/v solid)
o Eg: zinc oxide suspension

Question 9

based on nature of solid particles

Answer 9

 Flocculated suspension
 Deflocculated suspension

Question 10

based on size of solid particles

Answer 10

 Colloidal suspensions (< 1 micron):
o Suspensions having particle sizes of suspended solid less than about 1micron in size are called
as colloidal suspensions.
 Coarse suspensions (>1 micron):
o Suspensions having particle sizes of greater than about 1micron in diameter are called as coarse
suspensions.
 Nano suspensions (10 ng):
o Suspensions are the biphasic colloidal dispersions of nanosized drug particles stabilized by
surfactants.
o Size of the drug particles is less than 1mm.

Question 11

flocculated

Answer 11

 In flocculated suspension the individual particles are in contact with each other to form loose
aggregates and create a network like structure.
 Although the rate of sedimentation is high but the sediment is loosely packed which can re dispersed
easily on shaking so as to reform the original suspension.
 However; the flocculated suspensions meant for oral, Parenteral ophthalmic or external use may not
be elegant because they are difficult to remove from bottles or vials and on transferring from the bottle
the floccules remain sticking to the sides of the bottle.
 These properties can be improved by adding protective colloids.

Question 12

deflocculated suspentions

Answer 12

 In nonflocculated or deflocculated suspensions all individual particles exist as sediment is
formed slowly but the sediment is closely packed due to weight of upper layers of sediment is closely
packed due to weight of upper layers of sediment materials.
 A hard cake is formed which is difficult to re disperse to get original suspension.
 The nonflocculated suspensions have pleasing appearance as compared to flocculated suspensions
because the substances remain suspended for a sufficiently long time.

Question 13

flocculated and deflocucated properties

Answer 13

Particles form loose aggregates and form a network
like structure.

Particles exist as separate entities.

Rate of sedimentation is high Rate of sedimentation is low

Sediment is rapidly formed Sediment is slowly formed
Sediment is loosely packed and does not form a hard
cake.
Sediment is very closely packed and a hard cake is formed

Sediment is easy to re disperse. Sediment is difficult to redisperse.

Suspension is not pleasing in appearance. Suspension is pleasing in appearance.

The floccules stick to the sides of the bottle. They do not stick to the sides of the bottle.

Question 14

formulation of suspention

Answer 14

 The proper formulation is a key in the proper functioning, physical and chemical state of an ideal
suspension.
 In addition to functional and organoleptic additives (for example, vehicles, stabilizers, colorants,
flavourants and sweetening agents etc.).
 Suspension has also another group of additives, among these following are important.

Question 15

suspending and thickining agents

Answer 15

 These are pharmaceutical additives which increase the apparent viscosity of continuous phase and so
preventing the rapid sedimentation of dispersed particles for example, gum acacia, gum tragacanth,
sodiumcar boxy methylcellulose.
 Methyl cellulose, hydroxyl propyl cellulose, hydroxyl methyl cellulose, betonies etc.

Question 16

wetting agents

Answer 16

 In some cases, dispersed particles have affinity towards vehicle and so easily wetted by it.
 And when they have very little or no affinity towards the vehicle then wetting agents are used.
 They remove the air film b/w vehicle and solid particles and so vehicle can easily penetrate in to solid
particles. For example, surfactants, hydrophilic polymers (Acacia, colloidal SiO 2etc ) and hydrophilic
liquid (alcohol, glycerol etc).

Question 17

dispersing agents

Answer 17

 These are pharmaceutical additives which are used to get the uniform distribution and dispersion of
solid particles of dispersed phase.
 And they are usually used when the suspension are deflocculated in nature.
 For example, surfactants.

Question 18

flocculating agents

Answer 18

 These are the substances which are added to the suspension to cause controlled aggregation of particles
of dispersed phase.
 They include surfactants, electrolytes and hydrophilic polymers (tragacanth) cellulose derivatives etc.

Question 19

antioxidants

Answer 19

 These are the pharmaceuticals additives which are added to the suspension in order to prevent the
oxidative degradation of labile substances of the products.
 For example, ascorbic acid, tocopherol, butylated hydroxyl toluene etc.

Question 20

anti-microbial preservatives

Answer 20

 These are the pharmaceutical additives which are used in to formulation of suspension in order to
prevent the growth of microorganisms.
 They include chloroform, benzoic acid, ethanol etc.

Question 21

flavouring agents

Answer 21

 These are the substances which are added to the pharmaceutical preparations to mask the unpleasant
taste and odour of medicaments.
 That make the medication more acceptable to the patient. For example: cinema butter scotch, chocolate
and various fruit syrups.

Question 22

colouring agents

Answer 22

 They are added to the formulation to mask the unpleasant appearance and chlorophyll, riboflavin,
saffron, xanthophylls etc.

Question 23

formation of suspesion

Answer 23

The preparation of suspension is somewhat easy to other pharmaceutical dosage forms. During the
preparation of suspension following are the mask factors:

1. Particle size
2. Addition of additives
3. Method of mixing.

Question 24

particle size

Answer 24

 The basic step in the preparation of an ideal suspension is to obtain the particle size of proper range.
 The solid particle size of an oral suspension is such that it should not feel gritty to the skin.
 For topical suspension the particle size in the range that preparation should feel smooth to touch
whereas for inject able suspension should not case tissue irritation.
 On the other hand, the particle must not be so small that which again cause problems during the
formation of an ideal suspension.

Question 25

addition of additivatives

Answer 25

 In addition to principal and organoleptic additives. Some additional additives are also added to increase
viscosity.
 Wetting agents to reduce interfacial tension and facilitate the wetting of the dispersed particles.

Question 26

principle of mixing

Answer 26

 After achieving uniform particle size and addition of additives, the other main factor is the proper
dispersion of the solid particles. Depends upon:
o Proper flow of vehicle
o Sufficient shear
 The proper flow of the vehicle must be attained so that the solid particles uniformly dispersed in the
vehicle. In both cases, that vehicle is less viscous or more viscous.
 It does not favour the ideal suspension. A sufficient shear must be given to the system to achieve the
dispersion of individual particle rather than floccules.
 Along with these two factors, size and location of impeller, speed of impeller, presence or absence in
the container also effect the mixing of the systems.

Question 27

small scale processing

Answer 27

 On small scale processing of suspensions, pestle and mortar are used following steps are involved in
this process.
 The insoluble drug is triturated in pestle and mortar to fine size particle.
 The suspending agent is added with small amount of water to form mucilage.
 The mucilage and powdered drug is levigated to form paste. the suspending agents helps the uniform
dispersion of particles.
 The paste is mixed with remaining vehicle (containing soluble drugs, colorants, flavourants)
 The vehicle is added in portions to get the desired volume.
 Sometimes, the dispersion of final product is improved by passing suspension through a homogenizer
or colloidal mill.

Question 28

large scale proecessig

Answer 28

 The drug particles are treated with small portion of water (containing wetting agents) and allowed to
stand for several hours. During this period the entrapped air is released and drug is uniformly wetted
by vehicle.
 The suspending agents is dispersed in the external phase and allowed to stand until complete hydration
takes place.
 The wetted drug is added portion wise in the dissolved suspending agents.
 Other excipients such as electrolytes and buffer should be added with care to prevent variation in
particle charge.
 The other pharmaceutical additives such as flavouring, colouring, sweetening agents are also added.
 After complete mixing different ingredients of suspension, the product is subjected to suspension
equipments (either colloidal mill or homogenizer) in order to reduce the particle size and to form a
suitable preparation.

Question 29

theoritical consideration of suspentions

Answer 29

 A knowledge of the theoretic considerations pertaining to suspension s technology ultimately help
formulator to select ingredients that are
o Appropriate for suspension preparation
o That are available for milling
o Mixing equipment
 Some theoretic considerations are:
o Particle size control
o Wetting
o Sedimentation
o Brownian movement
o Electokinetic
o Aggregation

Question 30

partice size control

Answer 30

 Particle size of any suspension is critical and must be reduced within the range
 Too large or too small particles should be avoided.
 Larger particles will:
o Settle faster at the bottom of the container
o Particles > 5 μm impart a gritty texture to the product and also cause irritation if injected or
instilled to the eye
o Particles > 25 μm may block the needle
 Too fine particles will easily form hard cake at the bottom of the container.

Question 31

wetting of the particles

Answer 31

 Hydrophilic materials (talc, ZnO, Mg2CO3) are easily wetted by water while hydrophobic materials
(sulphur, charcoal) are not due to the layer of adsorbed air on the surface.
 Thus, the particles, even high density, float on the surface of the liquid until the layer of air is displaced
completely.
 The use of wetting agent allows removing this air from the surface and to easy penetration of the
vehicle into the pores.
 However hydrophobic materials are easily wetted by non-polar liquids.
 The insoluble medicament may be:
o Diffusible solids (dispersible solids): These are insoluble solids that are light and easily wetted
by water. They mix readily with water, and stay dispersed long enough for an adequate dose to
be measured. After settling they redisperse easily.
 Examples include magnesium trisilicate, light magnesium carbonate, bismuth
carbonate and light kaolin

o In-diffusible solids: Most insoluble solids are not easily wetted, and some particles may form
large porous clumps in the liquid, whereas others may remain on the surface. These solids will
not remain evenly distributed in the vehicle long enough for an adequate dose to be measured.
They may not redisperse easily.
 Examples for internal use includes aspirin, phenobarbital and sulfadirnidine, and for
external use calamine, hydrocortisone, sulphur and zinc oxide.

 Because of the high interfacial tension between indiffusible solids and water; air may be trapped in
these poorly wetted particles which causes them to float to the surface of the preparation and prevents
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.

Question 32

wetting agents

Answer 32

 Hydrophilic colloids such as acacia and tragacanth can act as wetting agents.
 Intermediate HLB (hydrophilic-lipophilic balance) surfactants such as polysorbates (tweens) and
sorbitan esters (spans) are used for internal preparations. While Sodium lauryl sulphate is used in
external preparations.
 Solvents such as ethanol, glycerol and the glycols also facilitate wetting.

Question 33

sedimentation

Answer 33

Sedimentation means settling of particle (or) floccules occur under gravitational force in liquid dosage
form. Velocity of sedimentation is expressed by Stoke’s equation:

vsed. =
d
2
(ρs − ρo
)g
18η0
=
2r
2
(ρs − ρo
)g
9η0

Question 34

limitation of stokes equation

Answer 34

Stoke’s equation applies only to:
 Spherical particles in a very dilute suspension (0.5 to 2 gm per 100 ml)
 Particles which freely settle without collision
 Particles with no physical or chemical attraction.

Question 35

sedimentation parameters

Answer 35

Sedimentation volume (F) or height (H) for flocculated suspensions:

Definition:
Sedimentation volume is a ratio of the ultimate volume of sediment (Vu) to the original volume of
sediment (VO) before settling.

F = V u / VO
Where,
 Vu = final or ultimate volume of sediment
 VO = original volume of suspension before settling

Question 36

physical proprties of dispersed particles

Answer 36

 Uniform dispersion of particles is the main factor in the formation of an ideal suspension.
 Uniform dispersion of particles depends on the physical stability of particles which in turn depends on
the following three important factors.
o Particles vehicles interaction
o Particle – particle interaction
o Rheology of suspension

Question 37

particles-vehicle interations

Answer 37

 The particle vehicle interaction is responsible for wetting of particles with vehicle and the uniform
dispersion of particles. So if particle vehicle interaction is good, then there will be formation of a good
suspension.
 As we increase the surface area by reducing the particle size, the interfacial tension and surface free
energy of particles are also increased.
 Due to this reason the particles with increased surface free energy tends to agglomerate in order to get
low surface free energy.
 This agglomeration is commonly known as flocculation. And this process does not favour an ideal
suspension.
 A suspension will thermodynamically stable if interfacial tension or surface free energy is zero. The
interfacial tension is reduced by using surfactants.
 As these surfactants cannot exactly make the interfacial tension zero, and promote the dispersion of
particles in vehicle by removing air film between particles and vehicle. So they are called wetting
agents.
 There are certain particles, with are not wetted easily by vehicle. Such particles are known as
hydrophobic particles. For example, sulphur or magnesium stearate in water.
 There wet ability may be increased by passing them through colloidal mill in the presence of wetting
agents (alcohol glycerine etc.).
 On the other hand, there are certain types of particles which are easily wetted by vehicle and such
particles are called lyophilic particles. For example, Talc and magnesium carbonate in water.

Question 38

particle-particle interaction

Answer 38

 Attraction or repulsion b/w particles of suspension are due to the presence of charge (forces) present
on the surface of the particles or due to the distribution of ions around them.
 This interaction b/w the particles lead to flocculation or de flocculation.
 If the particles of suspension have some charges i.e. either negative or particles have opposite charges
i.e. some have positive and some have negative, then there will be flocculation.
 In some cases, the surface of the particles may adsorb the ion of oppose charge. This adsorption of
opposite charges is called salvation. This effect also prevents flocculation.
 Flocculation results from the collision and combination of particles suspension.
 If they are protected by a barrier of electric charge on adsorbed molecule then all collision will not
result in combination of particles (& thus flocculation).
 Greater the protective barrier slower will be the rate combination of particles.

Question 39

rheology of suspension

Answer 39

 The rheological properties are of particular importance in formulating ideal suspension.
 The rheological property of a suspension mainly depends the degree of flocculation in the suspension.
 If there is flocculation in to product, there will be decrease in the apparent viscosity flocculated
suspension, there types of non-Newtonian flows are observed. If the forces responsible for flocculation
with stand weak external stress then it will have some yield value, below which it will have some
characteristics of solid when the liquid stress with increase in the stresses, thus flocculated suspension
will tend to exhibit plastic or pseudo plastic behavior.
 If the breakdown or reformation of floccules is time dependent, then to thixotropy will be observed.
 On the other hand, deflocculated suspensions (having low dispersion particle concentration i.e. 10%)
show the Newtonian flow. So they are easily poured and spread on the skin.

Question 40

stability of suspentions

Answer 40

 One aspect of physically stability I pharmaceutical suspensions is concerned with keeping the particles
uniformly distributed throughout the dispersion.
 While it is seldom possible to prevent settling completely over a prolonged period of time, it is
necessary to consider the factors which influence the velocity of sedimentation.

Question 41

advantages of suspension

Answer 41

 The drugs which are unstable in aqueous medium can be formulated in suspension forms in
nonaqueous solvents.
 Drugs with unpleasant taste in solution form can easily be formulated as
 suspension to provide palatable medication.
 Suspension is an ideal dosage form to those patients who cannot swallow tablets or capsules.
 They prolong the action of drugs by using their derivatives in suspension form.
 Suspension for external use have fine particles size and so avoid the gritty feelings to the skin.
 Sterile suspensions are injected hypodermically to produce sustained action.
 Example:
o Suspension are given by oral route, external applications, and Parenteral use inhaled to lungs
& used for ophthalmic purposes in the eyes.
o The drugs which are available in the form of suspensions include analgesics, antipyretics,
antibiotics, antifungal, antacids etc.

 For example:
o Calpol suspension
o Ponstan suspension
o Vermox suspension
o Amoxil suspension
o Erythrocin suspension

Question 42

suspentions for oral administration

Answer 42

 These suspensions are administrated when there is a difficulty in the swallowing of other solid dosage
forms (such as tablets or capsule) or the drug has unpleasant taste or odour.
 For example, chloramphenical etc as these are orally administered, so colouring, flavouring, and
sweetening agents are also added to the formulation.
 Examples of orally administered drugs are antacid (e.g. aluminium hydroxide, magnesium hydroxide)
paracetamol suspension, Ponstan suspension etc.

Question 43

suspension for injections

Answer 43

 Such suspensions have particle size such that they can easily pass through syringe needle and for this
purpose their crystal should be of needle type.
 Such preparations are of particular importance in the field of depot therapy.
 For example, kenokortA, Depo provera, solucortif etc.

Question 44

suspentions for topical use

Answer 44

 In such type of suspensions, the particle size should be in the range that they cannot produce gritty
feeling on the skin. Such suspensions are of prime importance in pharmacy.
 Their best examples are lotions (for example calamine) paste (zinc and salicylic acid paste and
magnesium sulphate paste) etc.