Powders- Definition, Classification, Advantages & Disadvantages, Methods of Preparation

Definition of Powders (pharmaceutics)

Powders are dry, finely divided solid dosage forms containing one or more drugs intended for internal or external use.

Classification of Powders

Powders are classified into:

Based on use:

• Internal powders (oral use)
• External powders (applied on skin)

Based on dispensing:

• Bulk powders
• Divided powders (Chartulae)

 

Special types:

• Dusting powders
• Effervescent powders
• Dentifrices
• Douche powders
• Snuffs

Related Article: Eutectic Powder & Effervescent Powder | Classification of powder

Advantages & Disadvantages of Powders

Advantages of Powders:

• Faster absorption than tablets/capsules
• Flexible dosing
• Easy to prepare
• Suitable for large doses

Disadvantages of Powders:

• Bitter taste
• Stability issues
• Hygroscopic nature
• Difficult to mask taste

Dusting Powders

Definition Dusting Powders:

Finely divided powders applied externally to skin.

Types of Dusting Powder:

• Medical dusting powder (non-sterile)
• Surgical dusting powder (sterile)

Ideal Properties of Dusting Powder:

• Free flowing
• Non-irritant
• Fine particle size
• Good covering ability
• Sterile (for surgical use)

Effervescent Powders

Composition:

• Citric acid / Tartaric acid
• Sodium bicarbonate

 

Principle:

React in presence of water → release CO₂ gas → effervescence

 

Preparation:

• Dry mixing
• Granulation method (to avoid moisture reaction)

Hygroscopic, Deliquescent & Efflorescent

Hygroscopic:

• Absorb moisture from air
• Example: Sodium chloride

Deliquescent:

• Absorb moisture → form liquid
• Example: Calcium chloride

Efflorescent:

• Lose water of crystallization
• Example: Sodium carbonate

Handling:

• Use airtight containers
• Add adsorbents (e.g., starch)
• Double wrapping

Methods of Preparation of Powder

Trituration

• Grinding powders using mortar and pestle
• Used for particle size reduction and mixing

 

Levigation

• Reducing particle size by adding a small amount of liquid (levigating agent)
• Forms a smooth paste

 

Spatulation

• Mixing powders using a spatula on a slab
• Suitable for small quantities

 

Sifting

• Passing powders through a sieve
• Helps in uniform mixing and particle size control

 

Tumbling (for large scale)

• Mixing in a rotating container
• Used in industrial preparation

Mixing of Powders (Geometric Dilution)

• This method is used when one drug is in small quantity.

Method:

• Mix small amount of drug with equal amount of diluent.
• Continue stepwise until fully mixed.

Importance of Particle Size

• Due to the small size of the particles, they dissolve faster.
• Improves absorption
• Affects stability & uniformity

Packaging & Labeling

Packaging:

• Bulk powder should be stored in wide-mouthed containers.
• Divided powders should be stored in paper (like butter paper or wax paper).

Labeling:

• If it's for external use, then should be written that “For External Use Only”.
• Storage instructions should be there like "Store in cool and dry place away from sunlight".