Suspension – Pharmaceutics – I B. Pharma 1st Semester

Suspension

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

LIQUID
DOSAGE FORMS

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

Suspensions

• 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• Allows an accurate dose to be withdrawn.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

Sl.No

Flocculated suspension

Deflocculated suspension

1

Particles form loose aggregates or network like structure called
floccules.

Particles exist as separate entities.

2

Rate of sedimentation is high

Rate of sedimentation is less.

3

Sediment is rapidly formed

Sediment is slowly formed

4

Sediment is loosely packed and does notform a hard cake.

Sediment is closely packed and forma ahard cake.

5

Sediment is easy to redisperse

Sediment is difficult to redisperse

6

The supernatant liquid becomes clear very quickly

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

7

The floccules stick to the sides of the bottle

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

8

Product will not be pleasing in appearance

Product will be pleasing in appearance

                               

Summary

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

Leave a comment