Indiffusible solid substances will not remain distributed throughout the vehicle for enough time to ensure uniformity of dose. The stability of suspension and uniformity of dispersed substance are enhanced by increasing the viscosity of continuous phase by adding thickening/suspending agent.
Examples of indiffusible substances include Aspirin, Chalk, Phenobarbitone, Succinylsulphathiazole, Sulphadimidine (for oral use); and Calamine, Zinc oxide, Precipitated sulphur, Hydrocortisone, Triamcinolone acetonide (for external use).
Dispensing Method
Solid powders are finely divided by triturating in pestle and mortar with thickening agent. Make a cream of fine powder with 50% of vehicle and add more vehicle with stirring or triturating slowly. Remove foreign particles if visible in suspension by muslin cloth. Mix rinsing of mortar and pestle and add other liquid ingredient make up the volume by adding vehicle and mix properly by shaking the final product. Store in suitable container with label having ‘shake well before use’ instruction and dose.
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Method of dispensing:
Kaolin, chalk and bismuth carbonate are finely divided by triturating in pestle and mortar with tincture of catechu. Make a cream of fine powder with 50% of purified water and add more purified water with stirring or triturating slowly. Remove foreign particles if visible in suspension by muslin cloth. Mix rinsing of mortar and pestle and add other liquid ingredient make up the volume by adding vehicle and mix properly by shaking the final product. Store in suitable container with label having ‘shake well before use’ instruction and dose.