A pharmaceutical suspension is a dispersed system where insoluble particles are uniformly distributed throughout a liquid medium. Key aspects of suspensions include the particle size, shape, interactions, and use of suspending agents to decrease aggregation. Suspensions are used to deliver insoluble drugs and control drug release while masking unpleasant tastes. Quality is ensured through tests of sedimentation, rheology, stability, and redispersibility.

1. Pharmaceutical suspension
Faysal Ahmed
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2. A Pharmaceutical suspension is a disperse system in which internal phase is
dispersed uniformly as finely divided insoluble particles throughout the
external phase.
Suspension

3. The Difference Between Solution & Suspensions:
 When the 2 substances totally mix it is called a solution.
 E.g. Solute + Solvent = Solution
(sugar) + (water) = Solution
 We then say sugar is soluble in water, it has dissolved.

4. The particles in a suspension are insoluble
 Sometimes when we mix substances they stay in clusters. We therefore say it is
insoluble in water.
 E.g. Chalk + Water = Suspension
 Eventually the particles sink to the bottom to form sediment.

5. Types of pharmaceutical suspensions:
 Antacid oral suspensions
 Antibacterial oral suspension
 Dry powders for oral suspension (antibiotic)
 Analgesic oral suspension
 Anthelmentic oral suspension
 Anticonvulsant oral suspension
 Antifungal oral suspension

6.  Classification:
 Based on General Classes :
Oral suspension
Externally applied suspension
Parenteral suspension
 Based on Proportion of Solid Particles:
Dilute suspension (2 to10%w/v solid)
Concentrated suspension (50%w/v solid)

7.  Based on Electro kinetic Nature of Solid Particles:
Flocculated suspension
Deflocculated suspension
 Based on Size of Solid Particles:
Colloidal suspension (< 1 micron)
Coarse suspension (>1 micron)
Nano suspension (10 ng)

9.  Formulating Consideration of Suspensions:
 Wetting agents
 Particle Size
 Particle shape
 Particle- particle Interaction
 Suspending agent

10.  Wetting agent:
 A substance is referred to as a wetting agent if it lowers the surface tension of a liquid
and thus allows it to spread more easily.
 It is the important factor to be considered for formulation of suspension because the
more the wetable particle the more stable the suspension.
 Wetting ability depends upon the angle of contact between the particle and the solvent
which should be less than 90 C.
 e.g: Polysorbate 80 etc.

11.  Particle size:
 It is critical part to be considered and the particle size must be reduced within the range.
 Too large or too small particles should be avoided.
 Large particles settle down faster.
 Smaller particles may form agglomerates.
 Required particles size maintained to form stable suspension.

12.  Particle shape:
 Spherical shape particles form the more viscous with low rate of sedimentation
of suspension that's why it is preferable over needle shaped particles.
 Particle- Particle Interaction:
A. Zeta potential
B. Deflocculation and
C. Flocculation.

13.  The zeta potential is defined as "the difference in potential between the surface of
tightly bound layer."
 If the zeta potential is reduced, the attractive forces exceed the repulsive forces and the
particles come together, this phenomena is known as flocculation

14. B. Flocculated Suspension:
 In flocculated suspension, formed flocs i.e. loose aggregates will increase in
sedimentation rate due to increase in size of sedimenting particeles.It also depends
upon the porosity of flocs.

15. C. Deflocculated Suspension:
 In this, individual particles are settling, rate of sedimentation is slow, which prevents
entrapping of liquid medium which makes it difficult to redisperse by agitation. This
phenomena known as caking.
 The larger particles settle fast and smaller remain in supernatant so supernatent appears
cloudy.

16.  Suspending agent:
 They form film around particle and decrease the interparticle attraction.
 They also imparts viscosity to the solution.
 Examples: Sodium alginates, Methylcellulose, CMC, silicon dioxide etc.

17.  Reasons for the formulation of a suspension:
 when the drug is insoluble in the delivery vehicle.
 To mask the bitter taste of the drug.
 To increase drug stability.
 To achieve sustained drug release.

18.  Quality Control of Suspensions:
 Appearance Color, odor and taste
 Sedimentation rate and
 Zeta Potential measurement
 Sedimentation volume
 pH
 Redispersibility and Centrifugation tests
 Rheological measurement
 Stress test

19.  Advantages of Suspension:
 Suspension can improve chemical stability of certain drug. E.g. Procaine penicillin G
 Drug in suspension exhibits higher rate of bioavailability than other dosage forms.
 Bioavailability is in following order:
Solution > Suspension > Capsule > Compressed Tablet > Coated tablet
 Duration and onset of action can be controlled. E.g. Protamine Zinc-Insulin
suspension
 Suspension can mask the unpleasant/ bitter taste of drug. E.g. Chloramphenicol
palmitate

20.  Disadvantages of Suspension:
 Physical stability, sedimentation and compaction can causes problems.
 It is bulky, therefore sufficient care must be taken during handling and transport.
 It is difficult to formulate.
 Uniform and accurate dose can not be achieved unless suspension are packed in
unit dosage form .

21.  Pharmaceutical Application of suspension:
 Suspension is usually applicable for drug which is insoluble or poorly soluble.
E.G. Prednisolone
 Suspension to prevent degradation of drug or to improve stability of drug. E.G.
Ox tetracycline suspension
 To mask the taste of bitter of unpleasant drug. E.G. Chloramphenicol
palmitate suspension
 Suspension of drug can be formulated for topical application E.G. Calamine
lotion.