Pharmaceutical suspensions are heterogeneous mixtures containing solid particles dispersed in a liquid medium. They allow insoluble drugs to be formulated into liquid dosage forms. Suspensions are administered via several routes including orally, ocularly, parenterally, and topically. Qualities of a good suspension include maintaining homogeneity during use and easy re-suspension of sediment. Suspensions have advantages over other dosage forms like permitting formulation of poorly soluble drugs and prolonging drug action.

1. Pharmaceutical Suspension
Sarder Istiaque Ahmed
111-29-308
Daffodil International University

2. • A heterogeneous two phase mixture containing
solid particles that are sufficiently large for
sedimentation.
• Usually they must be larger than 1 micrometer.
Disperse phase: Finely divided insoluble solid
particles (diameter of 1 µm to 100 µm )
Continuous phase: Liquid (usually aqueous)

3. Route of Administration
Oral -Antacid oral suspensions
Ocular-Prednisolone opthalmic suspension
Parenteral-Vaccines
Topical- Calamine Lotion

4. Why suspension ???
• If the drug is insoluble or poorly soluble in a
suitable solvent, then formulation as a
suspension is usually required.
• Prolonged contact between the solid drug
particles and the dispersion medium can be
considerably reduced.
• A drug that degrades in the presence of water
may alternatively be suspended in a non-aqueous
vehicle. Fractionated coconut oil is used as the
vehicle for some formulations of antibiotics for
oral use.

5. Qualities of a good suspension
 Must remain sufficiently homogeneous for at least the
period between shaking the container and removing
the required amount.
 The sediment produced on storage must be easily
resuspended.
 Any suspended particles should be small and uniformly.
 Resistance to microbial contamination.
 Should be chemically stable.
 Ideally, suspension should be thixotropic.

6. Advantages of suspension over other
liquid dosage form
 Permits the formulation of poorly soluble drugs as
liquid dosage form.
 Suspension can be used to prolong the action of drugs.
Higher bioavailability-
Solution > Suspension > Capsule > Compressed Tablet
> Coated tablet
 Certain drugs such as antibiotics that are unstable in
aqueous solution can be formulated as suspensions
 Drugs with unpleasant taste in solution such as
paracetamol can be formulated as suspensions.

7. Disadvantage of suspensions
 Suspension must be shaking well before use.
 Over the long period of time the two phase of a suspension may
separated out.
 Dispersed solute of a suspension may adhere to the opening of the
container, which may contaminate.
 Sometimes suspensions are of gritty feeling that is undesirable.

8. Classification
Based On Route of Application:
 Oral suspension e.g. antacid, antibiotic
 Externally applied suspension e.g. lotion
 Parenteral suspension
 Ophthalmic suspension
Based On Proportion Of Solid Particles
 Dilute suspension (2 to 10% w/v solid)
 Concentrated suspension (50% w/v solid)
Based On Electrokinetic Nature Of Solid Particles
 Flocculated suspension
 Deflocculated suspension

9. Theoretic consideration or factor
1. Wetting: By definition a suspension is essentially an incompatible
system, but to exist at all it requires some degree of compatibility,
and good wetting of the suspended materials is important in
achieving this goal.
2. Particle interaction and behavior

10. Discrete dispersion (Deflocculated suspension)
 Individual particle
 Sediments slowly
 Minimum sediment height
 Caking due to crystal bridging hence irredispersible
Open network aggregated dispersion (Flocculated suspension)
• Fibrous, fluffy, open network aggregation of particles
• Sediments rapidly
• High sediment height
• Easily redispersible

12. • 3. Sedimentation behavior: Sedimentation means settling of solid
particle or floccules occur under gravitational force in liquid dosage
form.
• Sedimentation volume is a ratio of the final or ultimate volume of
sediment (Vu) to the original volume of suspension (VO) before
settling.
 Expressed by “F”
F = V u / VO
or, F = H u / HO
Where, Vu = final or ultimate volume of sediment
VO = original volume of suspension before settling.
Hu = final or ultimate height of sediment
HO = original height of suspension before settling.

13. Sedimentation volume…….
F=0.5 F=1.0
Vo
Vu
Vo

14. Degree of flocculation-
ß = Ffloc / Fdefloc
(Vsed/Vtot)floc
= -------------------
(Vsed/Vtot)defloc
Here,
Ffloc = sedimentation volume of flocculated suspension
Fdefloc = sedimentation volume of deflocculated suspension

15. 4.Crystal habit: Crystal habit can be of great importance in suspension for-
 Re-dispersibility
 Sedimentation
 Physical stability
 Appearance.
5. Crystal structure factors: When there is no change in the crystal habit, the
following factors may still be considered ---
1. Drug decomposition lead into salting in or out.
2. pH change with the changes in the particle size distribution.
3. The effect of change in temperature.
•

16. Composition of Suspension
Components Function
API Active drug substances
Wetting agents Added to disperse solids in
continuous liquid phase. HLB value 7-
9. Tween, Span
Flocculating agents Added to floc the drug particles.
NaCl, KCl.
Thickeners Added to increase the viscosity of
suspension. Natural gum & Cellulose
derivatives
Buffers and pH adjusting agents Added to stabilize the suspension to a
desired pH range. Borate, phosphate
buffer

17. Components Function
Osmotic agents Added to adjust osmotic pressure
comparable to biological fluid.
Coloring agents Added to impart desired color to
suspension and improve elegance.
Preservatives Added to prevent microbial growth.
Methyl, propyl paraben.
External liquid vehicle Added to construct structure of the
final suspension.

18. Controlled flocculation
Flocculating agent
These are substances added to cause controlled
aggregation of particles of the dispersed phase in a
suspension. Examples of such agents include-
i. Electrolytes
ii. ii. Surfactants
iii. iii. Hydrophilic polymers

19. Packaging
Pharmaceutical suspensions for oral use are
generally packed in wide mouth container
having adequate space above the liquid to
ensure proper mixing.
Parenteral suspensions are packed in either
glass ampoules or vials.