Suspension - Pharmaceutics - I B. Pharma 1st Semester


Learning Objectives

At the end of this lecture, student will be able to

• Define the term suspension

• Classify Suspensions

• Differentiate flocculated and deflocculated suspensions

• Differentiate diffusible and indiffusible suspensions


Monophasic Liquid Dosage Forms (single phase)

Biphasic Liquid Dosage Forms (two phases)

Biphasic Dosage Forms

• Biphasic dosage forms are those which contain 2 phases:

1. Disperse phase / internal phase

2. Dispersion medium / continuous phase / external phase.

• There are two types: Suspensions & Emulsions

Suspensions: Insoluble solid in a solvent

Emulsions: Two immiscible liquids


• Are biphasic heterogenous systems

• Finely divided insoluble solid particles (disperse phase) - dispersed or suspended in a vehicle (dispersion medium).

• The diameter of the disperse phase- from 0.5 to 100 micrometer.

Advantages of Suspensions

• Insoluble drugs - more palatable.

• Insoluble drugs - more stable.

• Suspended insoluble powders - easy to swallow.

• Easy administration - bulk insoluble powders.

• Absorption quicker than solid dosage forms.

• Lotions - leave a cooling layer of medicament on the skin.

• Sustained-release preparations.

Disadvantages of Suspensions

• Requires shaking before use.

• Accuracy of dose - less than solution.

• Storage conditions can affect disperse system.

•Suspensions - bulky, difficult to transport and prone to container breakages.

Uses of Suspensions

• Oral administration: E.g Gelusil, Digene (antacids)

• External application: Calamine lotion (protective)

• Parenteral administration: Cholera Vaccine

Classification of Suspensions

1. Based on type of solids

- Diffusible suspensions

- Indiffusible suspensions

2. Based on flocculated systems

- Flocculated suspensions

- Deflocculated suspensions

3. Based on use

- Oral suspensions:

- For topical administration

- For parenteral use & inhalation therapy

Diffusible Suspensions

• Contain diffusible solids

• Light powders –insoluble/ very slightly soluble in the vehicle

• Readily mix with water

• Remain suspended throughout the liquid - for a sufficient time after shaking

• Allows an accurate dose to be withdrawn.

• On standing - insoluble solids settle at the bottom

• Require re - shaking of the bottle

E.g. CaCO3, light MgCO3, magnesium trisilicate, rhubarb powder & light kaolin.

Indiffusible Suspensions

• Contain indiffusible solids

• Heavy powders - insoluble in the vehicle

• On shaking - do not remain uniformly distributed in the vehicle

• Difficult to withdraw an accurate dose

• Suspensions contain a suspending agent / thickening agent

• Helps to delay the sedimentation rate & prevent the formation of aggregates

E.g. Calamine, Hydrocortisone, precipitated sulphur, Zinc oxide, Aspirin, chalk powder, Zinc oxide, Phenobarbitone

Flocculated & Deflocculated Suspensions


Flocculated suspension

Deflocculated suspension


Particles form loose aggregates or network like structure called floccules.

Particles exist as separate entities.


Rate of sedimentation is high

Rate of sedimentation is less.


Sediment is rapidly formed

Sediment is slowly formed


Sediment is loosely packed and does notform a hard cake.

Sediment is closely packed and forma ahard cake.


Sediment is easy to redisperse

Sediment is difficult to redisperse


The supernatant liquid becomes clear very quickly

Supernatant liquid will remain cloudy for a long time due to slow settling of particles.


The floccules stick to the sides of the bottle

The particles do not stick to the sides of the bottle.


Product will not be pleasing in appearance

Product will be pleasing in appearance



1.   Suspensions: Insoluble solid particles in a solvent

2.   Uses of Suspensions: Oral, Topical and parenteral

3.   Classification of suspensions

- Flocculated and Deflocculated suspensions

- Diffusible and Indiffusible suspensions

- Based on route of administration

4. Diffusible suspension: Suspensions containing diffusible solids and prepared without a suspending agent

5. Indiffusible suspensions: Suspensions containing indiffusible solids and prepared with a suspending agent

6. Flocculated suspensions:

- Solids form floccules

- Rate of sedimentation is high

7. Deflocculated suspensions:

- Individual particles

- Rate of sedimentation is low

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