Formulation of Suspension

Suspension are the biphasic liquid dosage form of medicament in which finely divided solid particles ranging from 0.5 to 5.0 microns are dispersed in a liquid (or) semisolid vehicle.

Good qualities of a suspensions

  1. It should settle slowly and should be readily redispersed on gentle shaking of the container.
  2. It should be chemically Inert.
  3. The suspension should pour readily and evenly from its container.
  4. It should be free from large particles, which spoil the appearance, gives a gritty taste to preparation, and cause irritation to tissues.
  5. The suspended particles should not form a cake.

Formulation of Suspension

Formulation of Suspension
  1. Flocculating Agent: In suspension, the solid particles are well dispersed in the dispersion medium, that is a vehicle. This can be improved by adding surfactants that act as flocculating agents. Ex: Sodium lauryl sulfate tweens, spans, and carbowaxes.
  2. Thickening Agents: These are hydrophilic colloids that form colloidal dispersions with water and maintain the viscosity of the continuous phase.

Thickening agents are classified into three major groups:

  1. Polysaccharides.
  2. Inorganic agent.
  3. Synthetic compounds.

Polysaccharides: two types of polysaccharides are used

a. Natural Polysaccharides:

i. Gum acacia: It is a good protective colloidal and suspending agent.

ii. Tragacanth: It is a better thickening agent than acacia.

iii. Starch: Starch is sometimes used with other suspending agent because of the high viscosity of its mucilage.

iv. Sodium Alginate: It forms a viscous solution when dissolved in water.

b. Semisynthetic Polysaccharides: These are cellulose derivatives.

i. Methyl Cellulose: It is generally used in the conc of 0.5 to 2% as a thickening agent.

ii. Sodium Carboxymethyl Cellulose: It is used for oral, external, and parenteral use, in the concentration of 0.25 -1%

Inorganic Agents:

i. Clay: Bentonite and aluminum magnesium silicate is very commonly used as a thickening agent. Bentonite is used in the con. of 2% for external preparations, whereas aluminum magnesium silicate is used in both external and internal preparations.

ii. Aluminium Hydroxide: It is used as a suspending agent in a suspension containing barium sulfate, calamine, sulphonamide, and sulphur.

Synthetic Compounds:

i. Carbomer: It is used as a thickening agent, in the con. of 0.1 0.4% for internal and external preparations.

ii. Colloidal silicon dioxide: It is a white non- gritty powder.

3. Wetting Agents: The substance which reduces the interfacial tension between the solid particles and liquid medium, producing a suspension of the required quality. Ex: Alcohol in tragacanth mucilage, glycerin in sodium alginate.

4. Preservatives: A suitable preservative is needed to preserve suspensions against bacterial growth. Preservatives should be effective against a wide range of microorganisms. Ex: Benzoic acid, sodium benzoate, methylparaben.

5. Organoleptic Additives: Colouring agents, sweetening agents, and flavoring agents are generally used in oral suspensions.

Also read: Identification test for emulsion

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