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• Allows an accurate dose to be withdrawn.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