Download Mixing of Powders

Powders
A Pharmaceutical powder is a mixture of finely divided •
drugs or chemicals in a dry form meant for internal or
external use.
Advantages of powders : •
1-flexibility of compounding. •
2-Good chemical stability •
3-Rapid dispersion of ingredients (because of small •
particle size
Disadvantage of powders:
1-Time-consuming preparation
2-Inaccuracy of dose( size of measuring
spoon, density of powder, humidity, degree
of settling , fluffiness.
3-Unsuitability for many unpleasant tasting,
hygroscopic and deliquescent drugs
Powders As a Dosage Form
Bulk and Divided
A – Bulk Powders
Definition: Pharmaceutical
powders dispensed as a whole in
one container
Types: 1- Oral powders:
Examples: Antacid powder
Oral antibiotic powder
2- Bulk powders for external use
Examples: •
-
Douche powders •
Dentifrice powders •
Triturates •
Insufflations •
Dusting powders •
B- Divided powders
Definition: Pharmaceutical
powders dispensed as divided
doses
Examples:
- Packets
- Cachets
- Powders for injection
Bulk Powders
may be classified as oral powders, dentifrices, douche
powders, dusting powders, insufflations and
triturations.
Oral Powders - These generally are supplied as finely
divided powders or effervescent granules. The finely
divided powders are intended to be suspended or
dissolved in water or mixed with soft foods, e.g.,
applesauce, prior to administration.
Antacids and laxative powders frequently are
administered in this form
Effervescent granules
* Contain sodium bicarbonate and either citric acid, tartaric
acid or sodium biphosphate in addition to the active
ingredients.
* On solution in water, carbon dioxide is released as a
result of the acid-base reaction. The effervescence from
the release of the carbon dioxide serves to mask the
taste of salty or bitter medications.
* The completed product must be dispensed in tightly
closed glass containers to protect it against the
humidity of the air.
Effervescent powders
- Other preparative techniques have been reported for effervescent
powders such as a fluidized-bed procedure in which the
powders are blended and then suspended in a stream of air in a
Wurster chamber. Water is sprayed into the chamber resulting
in a slight reaction and an expansion of the particles to form
granules ranging in size from 10- to 30-mesh.
•
Dentifrices
These may be prepared in the form of a bulk •
powder, generally containing a soap or
detergent, mild abrasive and an
anticariogenic agent.
Douche Powders
These products are completely soluble and are intended to
be dissolved in water prior to use as antiseptics or
cleansing agents for a body cavity.
They most commonly are intended for vaginal use, •
although they may be formulated for nasal, otic or
ophthalmic use. Generally, since aromatic oils are included
in these powders.
Dispensing in wide-mouth glass jars serves to protect
against loss of volatile materials and permits easy
access by the patient
•
•
Dusting Powders
Dusting powders are applied to various •
parts of the body as lubricants,
protectives, absorbents, antiseptics,
antipruritics, anti bromhidrosis agents,
astringents and antiperspirants.
Insufflations
- These are finely divided powders
introduced into body cavities such as the
ears, nose, throat, tooth sockets and
vagina. An insufflator (powder blower)
usually is employed to administer these
products.
Insufflations
However, the difficulty in obtaining a •
uniform dose has restricted their general
use.
Specialized equipment has been •
developed for the administration of
micronized powders of relatively potent
drugs. The Norisodrine Sulfate Aero haler
Cartridge (Abbott) is an example.
Divided Powders
Are dispensed in the form of
individual doses and generally are
dispensed in papers, properly folded
(chartulae). They also may be
dispensed in metal foil, small heatsealed plastic bags or other
containers.
Divided Powders
- After weighing, comminuting and mixing
the ingredients, the powders must be
divided accurately into the prescribed
number of doses. In order to achieve
accuracy consistent with the other steps in
the preparation, each dose should
be weighed individually and transferred to a
powder paper. Following completion of this
step the powder papers are folded.
Official powdered Drugs
A- Official powdered vegetable drugs
B- Official powdered drugs
Check the USP, BP and SFDA
Mixing
Importance:
1.
2.
3.
Ensure an even distribution of the active
component(s)
Ensure an even appearance of the DF
Ensure that the DF releases the drug at the correct
site and at the desired rate
Mechanisms of Mixing:
1.Diffusion:Movement of single particles
2.Convection:Movement of groups of particles
3.Shear
:Sliding of particles in planes over each
other
Mixing of powders
Large-Scale Mixing Equipment
The ideal mixer should
1- produce a complete blend rapidly to avoid
product damage.
2- It should be cleaned and discharged easily
3- be dust-tight
4 require low maintenance and low power
consumption.
Mixers for Powders
Tumbling Mixers/Blenders
Barrel blender
V-shape blender
Tumbling Blenders
• Cube blender
Double cone blender
Tumbling Blenders
Factors affecting mixing efficiency by
tumbling mixers
1. Too high a rotation speed will cause the
material to be held on the mixer walls by
centrifugal force, and too low a speed will
generate insufficient bed expansion and little
shear mixing.
2. The addition of baffles or rotating bars will also
cause convective mixing, for example the
V-mixer with agitator bar.
3. Presence of significant difference in particle
size, as segregation is likely to occur.
Mixing of Powders
Extemporaneous Methods
1- Spatulation
2- Trituration
3-Levigation
Small-Scale Mixing Equipment
1- Spatulation
The blending of powders with a spatula on a tile or
paper used sometimes for small quantities or when
the mortar and pestle technique is undesirable.
It is not suitable for large quantities of powders or for
powders containing one or more potent substance
because homogenous blending may
not occur.
2- Trituration:
.
is used to comminute( reduce particle size) & to mix
powders.
1-A porcelin preferred than glass morter.
2- A glass morter is preferrable for chemicals that stain
a porcelin. When granular or crystalline materials
are to be incorporated in to powdered product ,these
materials are comminuted individually and then
blended together in the morter.
3- Levigation
In this process
A- paste is first formed by the addition of a
suitable non solvent to the solid material.
B-Particle-size reduction then accomplished
by rubbing the paste in a mortar with a
pestle or on an ointment’ slab using a
spatula.