Pharmaceutical Powders
Pharmaceutical Powders
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Classification of Powders :
1. Bulk Powders for internal use
2. Bulk Powders for external use
3. Divided (single dose) powders
Advantages of Powders:
1.When it is not possible to dispense a drug as a solution or a
suspension, because of its insolubility or because it is susceptible to
microbial continuation if it is wetted, then it is a good idea to
dispense it as a powder.
A Few decades ago, when crude vegetable drugs were the most often
prescribed drugs, dispensing them as powders was a good option.
Disadvantages of Powders :
1.They are time
consuming to prepare and pack.
2.
They
are bulky to
carry about.
3.
Powders
may spill
when they are being opened.
4.
When
a tablet or a
capsule is not suitable, a well
formulated suspension may be a suitable alternative.
5.When
a medicament
with an unpleasant taste has to be
administered, it may be given as a suspension or in a hard capsule form.
6.Powders
are not an
ideal way of dispensing substances
that are volatile deliquescent, hygroscopic or oxygen-sensitive.
A pharmaceutical powder is a mixture of finely divided drugs
and / or excipeitns in dry form, meant for internal or external use.
One of the following three methods was widely used by the
1.Trituration :
Trituration is a method by which we make coarse powders into
small particles by rubbing them in a mortar with a pestle. We also use
trituration to mix two dry powders.
2.Pulverization by
Intervention :
When it is difficult to powder a material in a mortar because
it is soft or gummy, we add a second material which helps in the
powdering and which is latter removed. So when material A resists
grinding, we add we can then grind them or pulverize them easily. Them
material B is removed. For example, powdering camphor is difficult, so
we add a small amount of alcohol to it and we them powder it, then we
allow alcohol to evaporate.
3.Levigation :
The substance is powdered by adding a suitable non solvent
(levigations agent) to it, to form a paste. We then rub the paste in a
mortar and pestle. Liquid Paraffin is a commonly used levigations
agent. This method is used to incorporate solids into dematologic or
ophthalmic ointments and suspensions to prevent a gritty feel.
Principles involved :
There are
four principles involved in the preparations of powders. These
principles are true for yester years powders and they are
true for the preparation of granules in todays manufacture
of tablets and capsules.
2. Fine size :
The size of the powder should be fine. Coarse powders are
difficult to swallow.
3. Free flowing :
The powders should not be wet. They should not be in lumps.
4. Good taste :
Unpleasant taste should not be there.
If it is there, it should be masked by adding sweetness.
5.Amount
should not be too large or too small.
Procedure :
These
points are achieved by preparing powders in the following way.
1. Geometric dilution :
In this
method we first take into the mortar, that drug which is minimum in
weight (say drug A, 500mg) we powder it with the pestle, then we add to
the mortar, the drug which is next higher in weight (say drug B, 1g);
we add into the mortar that much of the second material which is
approximately equal to the material in the mortar (500mg). We mix them
and then we add the remaining quantity of B and mix them. Them we add
the remaining drugs in order of increasing weights (say drug C, 2g;
drug D 3g etc.). Each time we add an amount that is equal to the amount
in the mortar. When we take the materials into the mortar in this way
and mix them, we get very good mixing.
2. Weighing :
After the material of the
powder is prepared it is divided into individual doses. In weighing
certain points are to be kept in mind. Today nobody is working in the
imperial system; but if you are working in the imperial system 1 grain
is the minimum that can be weighed and 2 grains are the minimum that
can be dispensed. In the metric system, by convention 100mg is the
minimum that can be weighed and 200mg is the minimum that can be
dispensed. If the final weight of a divided powder in coming out to be,
say 750mg, we take it to the nearest 100, that is 800mg, by adding an
inert diluent such as lactose to it. The final weight of a divided
powder or bulk powder is not allowed to be in a fraction or a part of
100mg.
3. Packing :
The packing of powders in done in a very systematic and specific manner.
Packs which
are known as pharmacists packs are prepared by folding a neatly cut
rectangular paper two times, each time keeping an edge. Then the final
pack has a central portion and two flaps. After placing the powder in
the center of the pack, the flaps are closed such that one flap goes
into the other.
4. Dispensing :
An envelope is taken and is neatly labeled. Below a sample
label is given.
Sponsored Links
Prescription No. 1
THE POWDER
3 DOSES
Take one dose when there is pain.
To,
Mr. P.Ajay,J. Vijaya Ratna,
26 years Pharmacist, Male Pedawaltair,
Visakhpatnam.
Visakhpatnam.
in the envelope and the envelope should be neatly sealed and dispensed.
Different
varieties of Powders :
1.Bulk
Powders for internal use :
When prescriptions contain large amounts of light drug
substances they fall into this category. We prepare a bulk powder, pack
the whole powder into one pack and send it with the instruction that
for every dose, the patient should take one teaspoonful of the
Gregorys powder NP whose formula is given below.
Formula :
Heavy Magnesium carbonate- 325 g
Light
Magnesium
Carbonate- 325 g
Rhubarb,in powder- 250 g
Ginger, in powder - 100 g
--------1000g
--------The Principle and the procedure are given in the last section
where 15 prescriptions are discussed.
(a) Medical :
They are used for superficial skin conditions, they should
not be used for application to open wounds or application or broken
skin. The label should clearly specify this point. We need not
sterilise the ingredients of these powders but we must be sure that
they are not containing pathogens.
(b) Surgical
These powders must be sterile because they are used in body
cavities and are applied on wounds. They are sprayed on burnt areas and
are placed on the umbilical cords of infants.
These powders usually contain an antibacterial agent. The
diluent is sterilizable maize starch, which is also called as
absorbable dusting powder.
(c) Insufflations :
These are fine powders which are used to produce either a
local effect, such as in the treatment of ear or nose or throat
infections or a systemic effect, such as when they are inhaled into the
lungs and get absorbed from the lungs. If a drug is destroyed in the
GIT, when it is taken orally, then making it into an insufflation is a
good option.
In fact this formulation is coming back into wide use now,
with the difference being that it is being manufactured in
pharmaceutical companies with the aid of the latest technologies.
Making a drug into a fine powder, packing it into containers called
inhalers, seeing that the powder goes and lodges in the lungs and then
releases the drug there involves a lot of technology. But if that can
be managed, it is a good dosage form, because absorption of drug from
the lungs is very fast, the lungs are highly perfused and the area
offered for absorption is equal to the area of a tennis court!
Divided Powders
Each dose of the powder is separately packed into a packet.
The number of packets in the envelope is the number of packets ordered
by the doctor. We usually proceed for 2 or 3 powders more than the
number ordered by the doctor, because some material may be wasted in
triturations and weighing. If all the materials or drugs present in a
powder are white in color, we usually add a drop of amaranth alcoholic
solution to the powder and go on mixing it. The end point of the mixing
would be the even spreading of the deep pink color of amaranth. If the
final weight of the divided powder is less than 200mg, we add enough
lactose as diluent to the whole mixture; such that the weight of
individual powder comes to 200mg. If liquids have to be made into free
flowing powders, we add enough lactose to absorb the liquid on to it.
We add enough lactose such that, when the final powder is divided into
doses, each dose is more than 200mg and is also rounded to the nearesh
100mg.
If a powder contains a potent medicine such as in the case of
codeine phosphate or Hyoscine hydrobromide we dilute them with
lactose
to bring them up to enough weight such that they can be dispensed.
If a powder contains a hygroscopic drug, the final powder is
double wrapped.
If a powder contains materials that form a eutectic mixture
the eutectic formation is allowed, and is absorbed onto a diluent the
final powder is sent in a double wrapped condition.