What is powders ?

Used to be described the physical form of a

material, that is, a dry substance composed of finely divided particles.

Chemical and Physical Features of Powders:• Morphology

• Purity

• Solubility

• Flowability

• Stability

• Particle Size

• Uniformity

• Compatibility

Particle Size and Analysis- The particles of

pharmaceutical powders and granules may range from being extremely course, about 10mm (1cm) in diameter, to extremely fine, approaching colloidal dimensions of 1um or less.

USP uses Descriptive Terms - Very Course, Coarse,

moderately Coarse, Fine and Very Fine, which are related to the proportion of powder that is capable of passing through the openings of standard sieves of varying fineness in a specified period while being shaken generally in a MECHANICAL SIEVE SHAKER.

Powders of Vegetable and animal Origin drugs Defined as:

•Very coarse (No.8): All particles pass through a No.8 sieve and not more than 20% pass through a No.60 sieve.

•Coarse (No.20): All particles pass through a No.20 sieve and not more than 40% pass through a No.60 sieve.

•Moderately Course (No.40): All particles pass through a No.40 sieve and not more than 40% pass through a No.80 sieve.

•Fine (No.60): All particles pass through a No.60 sieve and not more than 40% pass through a No.100 sieve.

•Very Fine (No.80): All particles pass through a No.80 sieve. There is no limit to greater fineness.

Important factors of Particle Size:

• Dissolution Rate of Particles

• Suspendability of particles

• Uniform Distribution of a Drug Substance

• Penetrability of Particles

• Lack of Grittiness of solid particles

Methods of Particle size:• Sieving – in which

particles are passed by mechanical shaking through a series of sieves of known and successively smaller size and the proportion of powder passing through or being withheld on each sieve is determined.

• Microscopy- in which sample particles are sized through the use of calibrated grid background or other measuring device.

• Sedimentation rate – in which particle size is determined by measuring the terminal settling velocity of particles

• Light energy diffraction or light scattering

• Laser holography

• Cascade impaction

• Online Methods

Comminution of Drugs

- Grinding a drug in a mortar to reduce particle size is termed trituration or comminution.

- Levigation is used in small-scale preparation of ointments and suspensions to reduce particle size and grittiness of the added powders.

Blending Powders

- When two or more powdered substances are to be combined to form a uniform mixture.

- It may be blended by Spatulation, Trituration, Sifting and Tumbling.

Medicated Powders

- Intended to be used internally and others externally.

- Medicated powders for external use are dusted on the affected area from a sifter-type container or applied from a powder aerosol.

Aerosol Powders

- Medicated powders that administered by inhalation with the aid of dry-powder inhalers, which deliver micronized particles of medication in metered quantities.

- Powder Blowers or insufflators may be used to deliver dry powders to various parts of the body.

Bulk Powders

- Bulk powders available in prepackaged amounts:

• Antacids (eg. Sodium bicarbonate)

Laxatives(eg. Psyllium)

• Douche Powders (eg. Massengil Powders)

• Medicated powder for external application

• Brewers yeast Powder

Divided Powders

- Prepared by pharmacist as follows:

• Using block-and-divide method

• Latter method for non potent drug

Papers used in Divided Powders:• Simple bond paper

• Vegetable parchment

• Glassine

• Waxed paper