Learning Objective

• Preparation of different types of suspensions

Suspensions Containing Diffusible Solids

The method of preparation of suspensions containing diffusible solids is as follows:

1. The drug is finely powdered with the other solid ingredients.
2. Three-fourths of the vehicle is added to the powder mixture and triturated to form a smooth cream.
3. More vehicle is added.
4. Any other liquid ingredients, if present, are added and the suspension is made up to volume.
5. The suspension is transferred to a bottle, corked and labeled. Example: R_xLight kaolin Light magnesium carbonate Sodium bicarbonate Peppermint water Labeling: SHAKE WELL BEFORE USE

Suspensions Containing Indiffusible Solids

The thickening agents used in indiffusible suspensions are given below:

1. Compound tragacanth powder: This is a mixture of powdered tragacanth (15%), acacia (20%), starch (20%) and sucrose. This powder is preferred when a vehicle other than water or chloroform water is used.
2. Tragacanth mucilage: This is a mixture of tragacanth powder, 90% ethanol and chloroform water. It is used only when the vehicle is water or chloroform water (because if it is added to preparations containing a medicinally active vehicle, the mucilage may replace the medicinally active vehicle, thereby decreasing its activity).The methods of preparing suspensions containing indiffussible solids are described below:
   1. Preparation using compound tragacanth powder
      1. The indiffusible solids are finely powdered and mixed with 2% w/w compound tragacanth powder.
      2. Three-fourths of the vehicle is added to the powder mixture and triturated to form a smooth cream.
      3. Any soluble ingredient is dissolved in the remaining vehicle and added slowly with trituration to the cream.
      4.  Any other liquid ingredients, if present, are added and the suspension is made up to volume.
      5. The suspension is transferred to a bottle, corked and labeled. Example: R_xBismuth carbonate Prepared chalk Kaolin Tincture catechu Water
   2. Preparation using tragacanth mucilage
      1. The indiffusible solids are finely powdered and mixed with soluble solids.
      2. The powder is then triturated with one-fourth the volume of tragacanth mucilage to form a smooth cream.
3.  One-half of the vehicle is then added.
4. Any other liquid ingredients, if present, are added and the suspension is made up to volume.
5. The suspension is transferred to a bottle, corked and labeled. Example:R_xAspirin Oxyphenbutazone Simple syrup WaterLabeling: SHAKE WELL BEFORE USE

Suspensions Containing Precipitate-forming Liquids

Liquid preparations containing resinous matter when mixed with water show precipitation of resin, which sticks to the sides of the bottle and will not diffuse on shaking. Examples are compound benzoin tincture and tolu tincture. To prevent this, suspending agent such as compound tragacanth powder or tragacanth mucilage is added.

Preparation Using Compound Tragacanth Powder

1. The diffusible and indiffusible solids are finely powdered and mixed with compound tragacanth powder.
2. Three-fourths of the vehicle is added to the powder mixture and triturated to form a smooth cream.
3. The precipitate-forming liquid is added in a slow stream into the center of the cream with rapid stirring.
4. Any soluble ingredient is dissolved in the vehicle and added slowly with trituration to the cream.
5. Any other liquid ingredients, if present, are added and the suspension is made up to volume.
6. The suspension is transferred to a bottle, corked and labeled.

Preparation Using Tragacanth Mucilage

1. Tragacanth mucilage is mixed with an equal volume of vehicle.
2. The precipitate-forming liquid is added in a slow stream into the center of mucilage with constant stirring.
3. Solid substances are dissolved in one-fourth of the vehicle and mixed with the above.
4. Any other liquid ingredients, if present, are added and the suspension is made up to volume.
5. The suspension is transferred to a bottle, corked and labeled.Labeling: SHAKE WELL BEFORE USE