Powders - Dosage Form Notes

Powders

Classification of Powders

• Bulk powders for external use: Non-potent substances.
• Bulk powders for internal use: Powders dispensed in bulk.
• Simple and compound powders for internal use.
• Granules or Effervescent granules.
• Powders enclosed in cachets and capsules:
  • Wafer Capsules
• Compressed tablets:
  • Tablets
  • Tablet triturates
• Hard Capsules

Bulk Powders for External Use

• Mixture of finely divided drug or chemicals in dry form.
• Four types:
  • Dusting powders: Medical, Surgical
  • Snuffs
  • Douche powders
  • Dental powder
  • Insufflation

Dusting Powders

• Meant for external application to the skin.
• Applied in a very fine state to avoid local irritation.
• Inert dusting powder bases: clay, kaolin, kieselguhr, magnesium carbonate, talc, starch
• Effective for absorbing secretions, draining congestion, imparting a cooling sensation.
• Extemporaneous dusting powders should be filtered through a 100-200 mesh sieve.
• Two types:
  • Medical:
    • Used for superficial skin conditions.
    • Not used for open wounds.
    • Dry powders dusted onto the skin using a sifter-topped container.
    • Ingredients need not be sterilized but must be pathogen-free.
  • Surgical:
    • Must be sterile.
    • Used in body cavities and on wounds.
    • Applied on burnt areas and umbilical cords of infants.
    • Contain an antibacterial agent.
    • Diluent is sterilizable maize starch.

Uses of Dusting Powders

• Functions: Lubricant, protective, adsorbent, absorbent antiseptic, astringent, antiperspirant, antipruritic
  • Lubricant: Reduces friction.
  • Protective: Dry film coat on skin against UV rays.
  • Adsorbent: Perfume held on the bulk.
  • Absorbent: Absorbs fluids oozing from the wound.
  • Antiseptic: Prevents infection.
  • Antiperspirant: Prevents sweat glands from secreting.
  • Antipruritic: Relieves itching.

Dusting Powder Requirements

1. Homogenous and very fine.
2. Free from irritation.
3. Flow easily.
4. Have good covering capacity.
5. Have good adsorptive and absorptive capacity.
6. Spread uniformly over the body surface.
7. Cling (adhere) to skin surface after application.
8. Protect the skin from irritation caused by friction, moisture, and chemical irritants.

Dusting Powders Application

1. Medicated dusting powders may be applied either to intact skin or to open wounds and mucous membranes.
2. Powders applied to open wounds must be sterilized.
3. Particle size should be very small; micronized or passed through a #100 sieve.
4. Highly sorptive powders should not be used on areas that exude large quantities of fluids to avoid hard crust formation.
5. Functions: Lubricants, protective, adsorbents, antiseptic, astringents, antiperspirants.

Dusting Powders Packaging

• Dispensed in sifter-top cans or pressurized packs (aerosols).
• Aerosols protect the powder from air, moisture, and contamination.
• Example:
  • Zinc oxide: $250$ g
  • Starch, in powder: $250$ g
  • Purified talc, sterilized: $250$ g
  • Action and use: Absorbent dusting powder, mild antiseptic.
  • Advice to patient: Dust lightly onto the affected area.

Snuffs

• Definition: Finely divided solid dosage forms of medicaments inhaled into nostrils.
• Function: Decongestion, Antiseptic, Bronchodilator
• Packing: Dispensed in flat metal boxes with hinged lid.

Dental Powders or Dentifrice

• Applied with a toothbrush for cleaning the surface of the teeth.
• Contain detergents, abrasives, antiseptics, coloring and flavoring agents in a suitable base.
• Base: calcium carbonate.
• Detergent: in the form of soap.
• Abrasive action: provided by finely powdered pumice stone.
• Essential oils: added to provide flavor and freshness to the mouth as well as antiseptic action.

Insufflations

• Definition: Medicated extremely divided fine dusting powders introduced into body cavities.
• An insufflation resulting from extemporaneous compounding must be passed through a size 100 mesh sieve before being administered.
• Pressured packages provide an excellent solution.
• Drug and other ingredients are packed into hard gelatin capsules. -After insertion into the insufflator the shell is broken and the flow release of powder is controlled by the patient's own respiratory effort.
• Packaging: Insufflators (powder– blower): difficult to obtain a uniform dose.

Dry-Powder Inhalers (Powder sprays)

• Dispensing powders under pressure will provide a uniform and targeted application, as opposed to simply dusting powders.
• A sterile environment can be maintained in an aerosol container for powdered medicines.
• To prevent clogging of the valve orifice and to maintain the uniform application of powder, the particles must be of a specific size range.
• For powder to be sprayed effectively, it must contain particles smaller than $50$ microns if it is to be packaged as a powder spray.
• The use of dry-powder systems for pulmonary drug delivery is now extensive.
• This dosage form has developed into one of the most effective methods of delivering active ingredients to the lungs for the treatment of asthma and chronic obstructive pulmonary disease.

Douche Powders

• Completely soluble to make a clear solution.
• Intended to be dissolved in water prior to use as antiseptics or cleaning agents for a body cavity.
• Most commonly are intended for vaginal use, although they may be formulated for nasal, otic, or ophthalmic use.
• The majority of douche powders will be used for their hygienic purpose, but some may contain antibiotics.
• Generally, aromatic oils are included in these powders pass through a No 40 or 60 sieve to eliminate agglomeration and ensure complete mixing.
• The ingredients in douche powder may contain volatile substances (e.g., menthol, thymol, and volatile oils).
• Several commercial douche powder packets come in metal foil bags.
• Each bag contains the appropriate amount of powder for one douche.
• Dispensing: Bulk-powder boxes may be used for dispensing douche powders although glass containers are preferred because of the protection offered by these containers against air and moisture.
• A certain volume of water is used to dissolve a teaspoonful or tablespoonful of powder so that the specified concentration is achieved.
• A pH of $3.5$ to $5$ is usually appropriate for the preparation of the solution.
• Numerous douches are also available in disposable applicators that have already been prepared for use.

Divided Powders

• A divided powder or chart is a single dose of powdered medicine in one or more individual packages, such as cellophane, metallic foil, or paper.
• The patient does not participate in the measurement process of powder divided into smaller dosage units, which makes them a more accurate dosage form than bulk powder.
• Divided powders are available in foil, cellophane, or paper packs, each providing better protection from the external environment due to their sealed nature.
• Cellophane, foil, and paper are all commercially available powders that protect themselves from external factors.

Bulk Powders for Internal Use

• For internal use.
• Supplied in a wide-mouthed container.
• Powders dispensed in bulk if accuracy of the dosage is not important.
• Taken with a teaspoon which can enter the bottle easily to remove the contents.
• Only the non-potent substances are supplied as bulk powders, e.g., antacids, laxatives, etc.
• Example: Gregory’s Powder

Simple and Compound Powders for Internal Use

• Divided Powders (Chartulae or powder paper):
  • Individual doses of powder packaged in folded or plastic bags.
  • Packets
  • Cachets
  • Capsules
• Undivided (Bulk) powders:
  • Dusting powder
  • Effervescent powder
  • Antacids, laxatives, dietary nutrient supplements
• Oral divided powder may contain one or more active ingredients together with an inert diluent to produce a minimum quantity of $120$ mg.
• Oral undivided powders are usually a simple mixture of the prescribed medication without additional ingredients.

Example of Undivided Oral Powder

• Prepare $100$ gram Compound magnesium Trisilicate Oral Powder BP 1988.
  • Ingredients
    • Magnesium trisilicate: $250$ g
    • Chalk, in powder: $250$ g
    • Sodium bicarbonate: $250$ g
    • Heavy magnesium carbonate: $250$ g
  • Action and Use: Adsorbent and antacid for treatment of dyspepsia.

Example of Divided Oral Powder

• Prepare Oral Rehydrated Salts BP 1988
  • Ingredient amount to prepare 1 litre solution
    • Sodium chloride: $1.0$ g
    • Potassium chloride: $1.5$ g
    • Sodium bicarbonate: $1.5$ g
    • Anhydrous glucose: $36.4$ g
  • Action and use: Rehydration and electrolyte replacement in treatment of diarrhea.

Problems Encountered in Powder Formulation

Hygroscopic and Deliquescent Powder

• Hygroscopic: powders which absorb moisture from the atmosphere.
• Deliquescent: powders absorb moisture to such extent that they become liquid.
• Examples: Ammonium chloride, Iron and ammonium citrate, pepsin, sodium bromide, sodium iodide, potassium citrate.
• Problem: Absorption of moisture from air leading to partial or complete liquefaction.
• Solution:
  • Applied in a granular form to decrease the exposed surface to air.
  • Packed in aluminum foil or in plastic film packets
  • Addition of light magnesium oxide to reduce the tendency to damp
  • Addition of adsorbent materials such as starch
• Dispensing method: Supply in granular form, double wrapping using aluminum foil.
• Examples:
  • halide salts (ex. Sod. Iodide)
  • Certain alkaloids (physostigmine HCl)

Efflorescent Powders

• Crystalline substances that liberate water of crystallization, wholly or partly, and become wet.
• Problem: Crystalline substances which during storage lose their water of crystallization and change to powder (to be efflorescent). The liberated water converts the powder to a paste or to a liquid.
• Examples: Alum, atropine sulfate, citric acid, codeine phosphate, Caffeine, ferrous sulphate, etc.
• Solution:
  • Using the anhydrous form and treating it in a manner similar to hygroscopic powders
  • Mixing inert substance with efflorescent substance

Eutectic Mixtures

• When two or more substances are mixed together, a new compound of lower melting point is created.
• Examples: Menthol, thymol, camphor, salol, aspirin, phenacetin, chloral hydrate.
• Problem: a mixture of substances that liquefy when mixed, rubbed, or triturated together. The melting points of many eutectic mixtures are below room temperature.
• Solution:
  • Using inert adsorbent such as starch, talc, lactose to prevent dampness of the powder
  • Dispensing the components of the eutectic mixture separately
  • Examples for absorbents: Magnesium carbonate, light magnesium oxide, kaolin, lactose, starch

Incorporation of Liquids

• Liquid included in some prescriptions
• Solution:
  • The liquid is triturated with an equal weight of the powder, and the remaining powder is added in several portions with trituration.
  • Adsorbent is incorporated, usually light kaolin.
  • Replace liquid extract with dry extract

Incorporation of Extracts

• Problem: Some plant extracts are available as powders or as semisolid (e.g., liquid extract of liquorice)
• Solution:
  • The powdered extracts have no problems and are treated generally as powders
  • Semisolid extract should be mixed with an equal quantity of lactose and reduced to a dry powder by evaporation before incorporation with other ingredients
  • Careful heating, if present, to save potency of the extract.

Volatile Substances

• Problem: The loss of camphor, menthol and essential oils by volatilization when incorporated into powders.
  • Some vegetable powders – contain volatile oils.
  • To prevent – Powder vegetable drugs lightly in mortar.
  • Double wrapping – can be done.
  • Inner wrapper – wax paper; Outer wrapper – any thick paper
• Solution: This may be prevented or retarded by use of heat-sealed plastic bags or by double wrapping with a waxed or glassine paper inside of a bond paper.

Potent Drug Substances

• Dose less than one grain / $60$ mg and poisonous substances.
• Potent drug + diluents. Triturated to weighable quantity.
• Problem: Limited precision and accuracy of the used balances to weight small amounts of potent drugs.
• Solution: Drug triturates:
  • Suitable diluents like lactose are mixed with the potent drug to form $10-20\% w/w$ drug triturates.
  • Very fine powders should be used in the triturates
  • Geometric dilution to prepare drug triturates

Incompatible Salts

• Problem: Chemically incompatible salts when triturated together produce discoloration, chemical deterioration or loss of potency.
• Solution:
  • Compounding such substances with minimum pressure
  • Use a convenient method for mixing the powder like tumbling in a jar or spatulation on a sheet of paper.
  • Each substance should be powdered separately in a clean mortar and then combined with other ingredients gently.
  • Powder and dispense separately.

Explosive Mixtures

• Problem: Oxidizing agents(ex. Pot. Salts of chlorate, dichromate, permanganate and nitrate- Sod. Peroxide- silver nitrate and silver oxide) explore violently when triturated in a mortar with a reducing agent ( ex. sulfides- sulfur- tannic acid- charcoal).
• Solution:
  • Comminute each salt separately.
  • Subject to a minimum pressure.
• EXAMPLE:
  • Oxidising agent + reducing agent - Explosion occurs.
  • Potassium chlorate + Tannic acid - Violent explosion.

℞

• Potassium chlorate – $0.6$ g
• Tannic Acid – $0.3$ g
• Sucrose – $0.3$ g