Powders and granules

What is a pharmaceutical powder?

A dry substance of finely divided particles used internally or externally.

What are the main uses of powders?(mind map)

Oral use; snuff; insufflation; topical application; preparation of solutions and douches.

What are the advantages of powders?

Good chemical stability; useful for bulky/high-dose drugs; easy to swallow; suitable for tube feeding; rapid dissolution and increased bioavailability.

What are the disadvantages of powders?

Require clear instructions; may have bitter taste; may degrade in humidity; sachets increase manufacturing cost; particles must be uniform and homogeneous.

How does particle size affect powders?

Smaller particles have greater surface area

How are powders classified according to dispensing method?

Divided powders; simple and compound powders for internal use; powders for reconstitution; bulk powders for internal use; bulk powders for external use.

What are examples of divided and bulk powders?

Divided: packets

What are the requirements of topical powders?

Uniform small particles; impalpable; free-flowing; adhere to skin; pass through at least a No. 100 mesh sieve.

What are topical powders composed of?

A base or vehicle; an adherent; and possibly an active ingredient and aromatic material.

What are insufflated powders?

Finely divided powders applied into body cavities such as the ears

What is a compound powder?

A powdered drug blended with other ingredients.

What are the forms in which powders may be prescribed?

Simple/compound internal powders; bulk external powders; granular effervescent powders; powders in capsules/sachets; compressed powders in tablets.

What are the main steps in processing powders?

Size reduction; sieving; weighing; mixing; packaging.

What is size reduction?

The reduction of larger particles into smaller particles of desired size and shape using external forces.

What are the objectives of size reduction?

Increase surface area; separate valuable constituents; achieve intimate mixing; dispose of solid waste; improve handling characteristics.

Why is particle size important in powders?

It affects dissolution rate

What happens when powder fill volume is not uniform?

The mass of drug incorporated changes

What are the USP classifications of powder particle size?

Coarse: >355 µm; moderately fine/coarse: 180–355 µm; fine: 125–180 µm; very fine: <125 µm.

What is sieve analysis used for?

Measuring particle size and ensuring appropriate weight and size distribution.

When is mechanical sieving most suitable?

When most particles are larger than about 75 µm.

Why are very small particles difficult to sieve?

Cohesion and adhesion cause particles to stick to each other and to the sieve.

How is a nest of sieves arranged?

Each lower sieve has a smaller aperture size than the sieve above it.

What techniques can machines use for sieving?

Shaking; vibration; air jets; ultrasonics for wet sieving.

What is mixing of powders?

The process of combining different powdered substances to form a homogeneous

What are the purposes of mixing powders?

Achieve uniform composition so small samples represent the bulk; promote physical or chemical reactions such as dissolution.

What factors should be considered when selecting a mixing process?

Material characteristics; mixing objectives; mixer selection; scale-up technique; equipment design and parameters.

What are the methods of mixing powders?

Spatulation; trituration; sifting; tumbling.

What is spatulation and when is it unsuitable?

Blending small amounts using a spatula on paper or an ointment tile; unsuitable for large quantities or potent substances.

What is trituration used for?

Comminuting and mixing powders; geometric dilution ensures uniform distribution of small amounts of potent substances.

What is sifting and what is its limitation?

Passing powders through sifters produces a light

What is tumbling?

Mixing powder in a rotating chamber; thorough but time-consuming.

What is a hygroscopic powder?

A substance that attracts water from its surroundings through absorption or adsorption.

What is a deliquescent powder?

A substance that absorbs moisture until it dissolves into a liquid solution.

What is a eutectic mixture?

Two or more substances that liquefy because the resulting mixture has a lower melting point than room temperature.

How are eutectic powders handled during dispensing?

Package each separately and instruct the patient to take them together; alternatively add an inert absorbent.

What is the correct method for mixing eutectic drugs with a diluent?

Each eutectic drug must first be mixed separately with diluent before the mixtures are combined.

What are efflorescent powders?

Crystalline substances that release water of crystallization during trituration

How should vegetable powders be triturated?

Lightly

How is a small amount of liquid incorporated into a powder?

Add the liquid to an equal amount of powder

What is granulation?

A size-enlargement process in which fine powder is agglomerated into larger granules with specific size

What are the reasons for granulation?

Avoid powder segregation; enhance flow; produce uniform mixtures; produce dust-free formulations; improve content uniformity; improve compaction.

What are the two types of granulation?

Wet granulation and dry granulation.

Why are granules used for reconstitution?

They protect drugs susceptible to hydrolysis or other degradation in water until dispensing

What are the typical sizes of granules?

Granules typically fall within the 4–12 sieve size range.

What granule size is commonly used for tablet manufacture?

Sieve 12–20

What are the general characteristics of granules?

They are agglomerated powder particles

What are the steps of wet granulation?

Weigh/blend ingredients; prepare damp mass; screen into granules; dry; size; add lubricant and blend; compress into tablets.

What happens during fluid-bed wet granulation?

Particles are suspended and dispersed while liquid excipient is sprayed onto them; drying forms granules or pellets of defined size.

What is dry granulation?

A process in which powder is compacted into large pieces and then broken down or sized into granules.

When is dry granulation especially useful?

For materials that cannot tolerate moisture or the elevated temperatures required for drying.

What are the two methods of dry granulation?

Roll compaction and slugging.

What is roll compaction?

Powder is compressed between mechanically rotating metal rolls into sheets or forms

What is slugging?

Compression of powder into large tablets or slugs

What are fines in slugging?

Powders that are not agglomerated into granules; they are separated

How do powders and granules compare in flow and stability?

Powders have poorer flow and are less stable; granules flow better and are more stable.

How do powders and granules compare in caking and wetting?

Powders are more likely to cake and are harder to wet; granules are less likely to cake and are easier to wet and dissolve.

How do powders and granules compare in compressibility and content uniformity?

Powders have poorer compressibility and more non-uniform dosing; granules have better compressibility and more uniform content.

How do powders and granules compare in dust and appearance?

Powders generate more dust and have less appealing appearance; granules generate less dust and have a more elegant appearance.

How do powders and granules compare in processing?

Powders have simpler processing; granules require more processing and exposure to heat and solvents.

How can granulated products be administered?

Measured and mixed with water/beverages; sprinkled on food; or eaten plain.

What are effervescent salts?

Granulated or coarse-to-very-coarse powders containing medicinal agents

What happens when effervescent salts are added to water?

The acids and base react and release carbon dioxide

Why are granules used instead of fine powders for effervescent products?

Larger particles dissolve more slowly

Why are citric and tartaric acids combined in effervescent granules?

Tartaric acid alone produces fragile granules that crumble; citric acid alone produces a sticky mixture that is difficult to granulate.

What is the fusion method for preparing effervescent granules?

Citric acid's water of crystallization acts as the binding agent; the mixture is heated

What are the important conditions for the fusion method?

Use acid-resistant equipment; mix rapidly in low humidity; heat at 34–40°C; sieve through 4

What is the wet method for preparing effervescent granules?

Water added to alcohol acts as the moisturizing agent; a pliable mass forms and is granulated and dried.