Pharmaceutical Technology II: Powders & Granules

External Powders

• Medicated powders for external use are dusted on the affected area from sifter-type containers or applied from a powder aerosol.
• These powders should bear a label marked "EXTERNAL USE ONLY".
• Powders for cutaneous application are presented as single-dose or multidose powders and should be free from grittiness.
• Powders intended for use on large open wounds or on severely injured skin must be sterile.

Dispensing of Powders

• Bulk powders can be provided to the patient in bulk or divided into single unit doses.
• Examples of bulk powders include:
  • Antacids (e.g., sodium bicarbonate) and laxatives (e.g., psyllium Metamucil)
  • Douche powders (e.g., Massengill Powder)
  • Medicated powders for external application to the skin (e.g., topical anti-infective, antifungal)
  • Brewer's yeast powder containing B-complex vitamins and other nutritional supplements

Divided Powders

• Divided powders are prepared by weighing or block-and-divide methods.
• Weighing method is used for potent drugs, where each portion is weighed separately before enfolding in a paper.
• Block-and-divide method is used for non-potent drugs, where the entire amount of powder is divided into smaller blocks.
• Papers used for packing powders include:
  • Simple bond paper
  • Vegetable parchment
  • Glassine
  • Waxed paper
• Moisture-resistant small cellophane or plastic envelopes may also be used to enclose individual doses.

Granules Dosage Forms

• Granules are aggregates of particles that form larger particles, usually in the 4-12-mesh size range.
• Advantage of granulation:
  • Improved flowability
  • Elimination of dust
  • Increased compressibility
  • Physical and chemical stability
  • Less likelihood of caking or hardening
  • Easier wetting by a solvent
• Examples of granules include:
  • Unstable antibiotic drugs in aqueous solution (e.g., KLACID granules, Augmentin ES-600)
  • Uricol granules
  • Effervescent granules (e.g., tablets)

Preparation of Granules

• Wet method:
  • Moisten the powder or mixture with a fluid (with or without a binder)
  • Pass the resulting paste through a screen of the desired mesh size
  • Dry the granules on drying trays by air or under heat
  • Screen and size the granules
• Dry method:
  • Pass the dry powder through a roll compactor and then through a granulating machine
  • By slugging, compress the powder mixture into large tablets or slugs, then granulate into the desired particle size
• Fluid bed processing can also be used to produce granules or pellets of defined particle size.

Effervescent Granulated Salts

• Effervescent dosage forms contain ingredients that release carbon dioxide when in contact with water.
• The wet method involves:
  • Mixing the powder with a liquid
  • Heating the mixture to release the water of crystallization from the citric acid
  • Rubbing the softened mass through a sieve to produce granules of the desired size
• The granules are then dried at a temperature not exceeding 54°C and placed in tightly sealed containers.