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Pharmaceutical Powders

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Smt. Dr. Jayanti Vijaya Ratna

Dear Students, Today I want to introduce to you one dosage
form which is called as “Powder”. Powders were very
popular dosage forms, once upon a time; at a time when it was common
practice for a pharmacist to “compound” a
prescription and dispense it. Today compounding is not thee and
“oral powders” are almost non existent. Only you
see occasionally, when old people or children cannot swallow tablets or
capsules; the tablets or capsules are made into powders, by the people
who are administering these medicines to them. Powders can be swallowed
more easily but their taste is also felt more by the tongue. Let us
today look at what are powders what are their advantages and
disadvantages and let us consider a few prescriptions for powders. I
want to just explain to you that the principles which are valid in the
preparation of powders at a compounding level are also equally valid in
the “manufacture” of powders or which are
ultimately becoming granules in the preparation of tablets.

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.
2.When a bulky drug that has a large dose is to be administered, a
powder is a good way of administering it. Several compound bulk powders
used to be there and mostly these were given for stomach conditions,
such as indigestion, constipation and diarhoea. They used to contain
large amounts of light materials such as Magnesium Carbonate. You can
see the prescription of Gregory’s powder, as an example for
this, in the last part of this article where prescriptions are
discussed (  
).
When we are using powders for this type of use, we give the instruction
“take a teaspoonful of the powder and swallow with
water”.
We can easily see that this is not an accurate way of administering
medicines, as the same weights of various medicaments often have
different volumes. So potent substances should never be given in the
form of bulk powders.
3.When tablets and capsules were not known administering insoluble,
potent substances as powders was an option. You can see the
prescriptions on codeine phosphate and Hyoscine hydrobromide as
examples for this principle in .
4.Small children and old people cannot swallow tablets and capsules. In
such situations powders are a good option.
5.Powders dispense fast in the Gastro Intestinal tract and the drugs
are absorbed faster from these. Whereas tablets have to disintegrate
first, the capsule shell has to dissolve first and then there may be
some problems because excipients are included in these.
6.When the patient has to mix the ingredients before administration,
dispensing in separate divided powders is a convenient way. See the
prescription on effervescent granules in .
7.Powders are very good from chemical stability point of view.

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
pharmacist, in yester years, for the preparation of powders.

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 year’s powders and they are
true for the preparation of granules in today’s manufacture
of tablets and capsules.

1.Drug Content Uniformity :  

When we are mixing
powdered drugs, the final objective is to produce such a powder which
is having drug content uniformity throughout. If the finished powder is
taken in a paper, any 100mg sample, taken from any corner or middle or
any place in it of the drugs should have the same ratio or the same
contents of the drugs involved in the prescription.

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.

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.

Labeling particulars change with each prescription. When
writing labels one should be very careful, no errors should be
committed, because the    
patient follows the labeling
instructions.

After neatly labeling the envelope the powders should be kept
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
Gregory’s 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.

2.Bulk powders for external use :

Dusting powders and insufflations come under this category.
Dusting powders are of two types :

(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!

The diluent usually used for insufflation is lactose. For
preparations meant for open wounds the diluent used is sterilisable
maize starch.

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.

If a powder contains an effervescent mixture, the acid and
the alkaline salt are separately packed and dispensed with suitable
directions.

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