Powders Flashcards
What are powders
- Solid materials in finely divided state (sometimes presented as granules).
- Powders may be formulated for external (topical) or internal (oral) use.
- May be supplied in bulk or individually wrapped or enclosed.
- May also be used in the process of manufacturing tablets, capsules and suspensions.
What is the importanceof particle size?
- Compound powders (ie more than one ingredient) need uniform particle size to avoid segregation on storage –> inaccurate dosing or inconsistent performance.
- Fine particle size is important for external (dusting) powders to avoid irritation – usually passed through a sieve with 180µm aperture (#80).
- Particle size of oral powders influences surface area –> affects rate of dissolution and onset of action.
- Also affects sedimentation rate if powder is being used to make a suspension. 180-350µm size usual for oral powders.
How does particle size reduction (comminution) occur?
Trituration – mortar and pestle (or industrial equivalent).
- Grinding of substance reduces particle size.
- Granular or crystalline substances should be ground separately before mixing.
- Mortar & pestle can also be used for mixing the comminuted powders.
- Glass mortars not suitable for hard solids
- Ware mortars not suitable for substances that stain or have a strong odour.
- Pestle must be correct size for mortar!
Pulverization by Intervention - used for hard crystalline or gummy substances (eg iodine, camphor)
- A volatile “intervening” solvent is used to dissolve the substance
- The solution is triturated and fine powder of the substance emerges as the solvent evaporates.
What is mixing and how does it occur
Mixing must be thorough to ensure homogeneity
Trituration using mortar and pestle - most common
- Avoid excessive force with pestle that may cause compaction of the powder.
- Use method of doubling (geometric dilution) for mixing ingredients for even distribution.
Spatulation - only used in special circumstances. Blending of powders using a spatula on sheet of paper, glass slab or mortar – no particle size reduction.
- Used to mix substances that form eutectic mixtures – blend each substance with an inert carrier and then blend together
what are external powders-dusting powders? What are some typical ingredients used in external powder
- Combination of 2 or more fine powders for external use.
- Could have single substance, but usually incorporated with a diluent which will reduce irritation and friction.
- Non-toxic, free of irritating properties, smooth.
- Have good covering properties and spread easily
- When supplied in bulk, a sifter or aerosol container should be used.
- May contain lubricants, protectives, absorbents, antiseptics, antifungals, antipruritics, antiperspirants, astringents or antibromhidrosis agents.
- Inert bases/diluents include Bentonite, Kaolin, Magnesium Carbonate, Starch and Purified Talc
- Powder bases absorb secretions and exert a drying effect –> a cooling sensation
Typical ingredients
Typical Ingredients:
- Starch, Purified Talc: Particles have flat surfaces, slide over each other – lubricant, improves distribution
- Zn, Mg & Al Stearates, ZnO & Colloidal Kaolin: Good adherence to the skin
- Light MgCO3, Zn Stearate & CaCO3: Provide lightness and bulk
- Titanium Dioxide, ZnO & Talc: Covering power and opacity
- Zn Stearate & ZnO: Soothing, protective, astringent
What are some medicines for external powders - dusting powders and what are their uses?
- Sulphur – antimicrobial
- Camphor, Menthol – cooling, antipruritic
- Chlorhexidine – antiseptic, antibacterial
- Miconazole, Tolnaftate – antifungals
What are medical powders and some of their use? How is it prepared and provide an example
Used for superficial skin conditions. Not intended for application to areas of broken skin or open wounds.
- Not sterile, but must be free of dangerous pathogens. Natural mineral ingredients (eg talc, light kaolin) may be contaminated with bacterial spores (eg C. perfringens, C. tetani, B. anthracis) and must have been sterilised
Uses
- Protection of skin
- Absorb moisture
- Reduce skin friction
- Cooling effect
- Discourage bacterial growth
- Action of added medicament
Preparation
- Prepared by trituration in a mortar and pestle using method of doubling (geometric dilution).
- Finished product is passed through 80-100 mesh sieve (150µm-180µm) before another light trituration to ensure uniformity.
Example
Aluminium Chlorhydroxide & Salicylic Acid Dusting Powder APF15 = Hyperhydrosis of the feet
- AC: treat hyperhyidrosis (lotta sweating), antiperspirant
- Salicylic acid (keratolytic)
- Purified talc, sterilised (absorbent, vehicle and easily spreadable)
What are containers for medical powders and what are some of the formulation considerations?
Sifter top container and aerosol (can keep contents sterile)
Formulation Considerations for Aerosols:
- For aerosols, active ingredient is suspended or dispersed in the propellant. • Particle size must be in defined range (2-8μm or less) to avoid clogging valve and facilitate uniform application.
- Need to avoid agglomeration of powder in can. Dispersing agents eg sorbitan trioleate reduce agglomeration
- Lubricants eg isopropyl myristate reduce friction between particles and lubricate components of the aerosol valve.
What are surgical powders and what are thier uses?
intended for use in body cavities, on wounds or on umbilical cords of babies.
- Must be sterile and presented in packaging that maintains sterility until time of use.
- Packs ≤30g with re-closable perforated lids or single use containers.
- May include antibacterial agents.
- Talc should not be used in these powders as it cannot be absorbed by the body and forms granulomas. Use Absorbable Dusting Powder USNF (Sterilisable Maize Starch PCx) as diluent.
- Prepared as medical powders with a terminal sterilization step.
Uses: Lubricants for surgical gloves
- Talc unsuitable
- Absorbable Dusting Powder USNF (Syn: Maize Starch Sterilisable BP 1973, Sterilisable Maize Starch PCx , Bio-Sorb®)
- Odourless, free-flowing powder
- Maize starch that has been treated to avoid gelatinising on exposure to moisture or steam sterilisation.
- Absorbable by tissues despite lack of solubility in water.
- Contains 2.2% MgO to increase lubricating properties and maintain fine powder form.
What are insufflations and what are some of the delivery devices?
Extremely finely divided powders intended for introduction into body cavities eg ears, nose, throat, tooth sockets, vagina, lungs.
- Extemp insufflations passed through 100 mesh sieve (≤150µm). Commercial pulmonary products micronised (1-6µm size).
- May be for local or systemic effect.
Delivered using
- Insufflator (powder blower) –> poor dose accuracy
- Directly inhaled into nostrils (cf snuff)
- Metered dose aerosol (asthma)
- Specialised breath activated inhalers (Dry powder inhalers)
What are the 7 types of internal powders and what are their advantages + disadvantages?
Internal powders
- Bulk Powders
- Granules
- Effervescent powders/granules
- Divided Powders (Chartulae)
- Powders for Injection
- Powders for Mixtures
- Veterinary Powders
Advantages
- Improved stability in solid state vs solution/suspension
- Suitable for children
- No disintegration step required, so improved dissolution and absorption rate cf tablets & capsules
Disadvantages
- May be awkward to transport
- Easily spilled
- Difficult to mask unpleasant taste
- Unsuitable for drugs that are inactivated by gastric acid.
What are bulk oral powders (internal powders)? What are some examples?
- Fine powder supplied in large quantity in a single container.
- Suitable for bulky drugs with large dose.
- Dispensed by the patient by volume eg 5mL metric teaspoonsful.
- Dosing is not very accurate as relationship between weight and volume depends on density of product.
- Only suitable for non-potent substances eg antacids, bulk laxatives.
- Intended to be dissolved or suspended in water, or mixed with soft food (by the patient) before administration – prevents choking.
- When constituents are volatile or deliquescent, airtight containers are required
- Can be inconvenient to transport
Examples
- Metamucil, inner health powder
- To prepare an extemporaneous oral bulk bowder –> mix powders in mortar and pestle using methods of doubling (geometric dilution). Liquid ingredients may be adsorbed onto one of the solid ingredients
- Not required to sieve oral powders
What are granules (internal powders)? What are some examples?
- In some instances it is desirable to granulate powdered ingredients.
- Involves blending of powders and then moistening with a solvent or binder to form a pasty mass. This is forced through a large mesh sieve and dried in an oven at low temperature.
- Granulation:
>avoids segregation of individual ingredients.
>allows addition of colouring and flavouring agents.
>produces an easily handled, attractive product.
- Granules may be swallowed whole, chewed, or dispersed in water or suitable liquid or soft food – depending on formulation.
- Granules may be uncoated, coated (to delay or prolong release of drug) or effervescent.
- Granulation is also a preliminary step in tablet manufacture.
- Examples: Normacol Plus® (laxative) – swallowed whole
What are Effervescent Powders & Granules (internal powders)? What are some examples?
- Supplied as fine powders or granules.
- When added to water these products effervesce (fizz) as CO2 is formed
- Carbonated solution masks the taste of the medicine.
- A combination of citric and tartaric acids are used along with sodium bicarbonate. When placed in water the chemical reaction between acid and carbonate releases CO2
- The water of hydration of the citric acid can be used to granulate the powders. Heating gently releases the water of hydration.
- Effervescent products must be kept in tightly closed containers to avoid access of moisture.
- May be supplied in single dose sachets.
- Examples: Eno®, Ural® , Gastrolyte Blackcurrant®
What are divided powders?
- For convenience or because of a need for accurate dosage (potent medications), powder (and granule) formulations may be supplied as individual powders (packets, sachets, capsules)
- Diluents are often used to produce single dose powders of minimum weight of 100-120mg.
- Diluent is commonly lactose – colourless, soluble and readily available. Starch is an alternative.
- Individual powders are presented wrapped in paper or in sachets.
- Taste masking is not always possible.
- Administered by placing powder on back of tongue and swallowing with glass of water or mixing with water before swallowing. Suitable for potent medications – accurate dosing.
