GATE:Pharmaceutical Powders
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Pharmaceutical Powders
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
- Bulk Powders for internal use
- Bulk Powders for external use
- Divided (single dose) powders
Advantages of Powders
- 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.
- 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 diarrhea. 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 ( 2.1 ). 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.
- 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 (2.5 &2. 6).
- Small children and old people cannot swallow tablets and capsules. In such situations powders are a good option.
- 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.
- 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 (2.13).
- Powders are very good from chemical stability point of view.
Disadvantages of Powders
- They are time consuming to prepare and pack.
- They are bulky to carry about.
- Powders may spill when they are being opened.
- When a tablet or a capsule is not suitable, a well formulated suspension may be a suitable alternative.
- When a medicament with an unpleasant taste has to be administered, it may be given as a suspension or in a hard capsule form.
- 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 excipients 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.
Methods of Preparation
- 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.
- 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.
- 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 dermatologic 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.
- 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.
- Fine size : The size of the powder should be fine. Coarse powders are difficult to swallow.
- Free flowing : The powders should not be wet. They should not be in lumps.
- Good taste : Unpleasant taste should not be there. If it is there, it should be masked by adding sweetness.
- Amount should not be too large or too small.
Dispensing Procedure
These points are achieved by preparing powders in the following way.
- 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.
- 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.
- 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.
- Dispensing : An envelope is taken and is neatly labeled. Below a sample label is given.
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
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
---------
1000 g
---------
The Principle and the procedure are given in the last section where 15 prescriptions are discussed.
Bulk powders for external use
Dusting powders
- 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.
- 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.
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.
Prescriptions
Aspirin Powder
Rx Aspirin – gr v Mitte tales decim Signa : Unam Somni nocte sumenda
Translation:
Rx Aspirin – 300 mg Send 10 powders. label: Take one at night.
Weight of one powder is 300 mg.
Principle : Single ingredient is there. So there is no need for any mixing. If the powder is coarse, it should be
made into a fine powder.
Procedure : Take the drug into a mortar and make it into a fine powder. Weigh out 300mg into each of 10 packets.
Neatly label the envelope, keep the packs in the envelope and dispense.
Prescription No 2
Rx Sodium bicarbonate – 300mg Activated Charcoal – 60mg Prepare powders and send six powders. Label : Take one powder after meals. Weight of one powder is 360 mg.
Principle : The two ingredients should be thoroughly mixed until the black colour of charcoal is uniformly
distributed.
Procedure : Calculate for 8 powders. Take 480mg of activated charcoal into a mortar. Add approximately equal amount
of sodium bicarbonate to it and mix thoroughly. Then add the remaining amount of sodium bicarbonate and mix thoroughly. Weigh out
360mg of the final powder into each of 6 packets. Put the packets in a neatly labeled envelope and dispense.
Prescription No 3
Rx
Phenacetini – gr iv Caffinae – gr i Fiat pulvis Mitte tales Decem Signetur : Capiat unum dolore urgente
Translation:
Rx Phenacetin – 240 mg Caffeine -- 60 mg Prepare a powder. Send 10 powders. Label: Take one when pain is severe.
Weight of one powder is 300 mg.
Principle :
Minimum weight that can be weighed is 100mg.
Minimum weight that can be dispensed is 200mg.
When both the ingredients are white in colour add a drop of amaranth, alcoholic solution to impart colour to the preparation.
Procedure :
Calculate for 12 doses.
- Take Caffeine 120mg into the mortar, powder it and add an approximately equal amount of Phenacetin and mix. Then add the remaining amount of Phenacetin and mix.
- Add a drop of alcoholic solution of amaranth and go on mixing until the colour is uniformly spread.
- Weigh out 300mg into each of ten packets and dispense in a neatly labelled envelope.
Prescription No 4
Rx Aspirin – 5gr Citric Acid – ½gr Calcium Carbonate – 1½gr
Label : The Powders
Dissolve in water and take when necessary. Send 12 powders.
Translation:
Rx Aspirin – 300mg Citric Acid – 30mg Calcium Carbonate – 90mg Label: The Powders Dissolve in water and take when necessary. Send 12 powders.
Calculations:
For 14 powders: Aspirin --- 4200mg Citric Acid --- 420 mg Calcium Carbonate —-- 1260 mg Lactose --- 1120 mg Weight of one powder is 500 mg.
Principle : Because citric acid is hygroscopic in nature the final powder should be double wrapped.
Procedure :
- Calculate for 14 powders.
- Add lactose to bring the final weight of each powder to 500mg
- Take 420mg of Citric Acid into mortar, add an equal amount of calcium carbonate and mix; then add the remaining amount of calcium carbonate and mix; then gradually add the lactose and the aspirin and thoroughly mix.
- Weigh 500mg into each of 12 packets, double wrap and dispense in a neatly labeled envelope.
- Double wrapping involves, spreading an inside layer of wax paper in each packet.
Prescription No 5
Rx Codeine Phos – gr 1/6 Fiat Pulvis : Mitte tales decem. Signa : Unus omni nocte sumendus.
Translation:
Rx Codeine Phosphate – 10mg Prepare a powder. Send 10 such powders. Label : Take one every night.
Calculations in Imperial System:
For 12 powders. Codeine phosphate – 2gr = 120mg Lactose (2x12) – 2gr – 22gr = 1320mg
Calculations in Metric System:
For 12 powders: Codeine Phosphate—120 mg Lactose -- 2280 mg Weight of one powder is 200 mg.
Principle: Codeine phosphate is a potent medicine and is prescribed in a small amount. It should be diluted with enough
lactose to bring it up to sufficient weight, i.e. 200 mg.
Procedure: Both are fine powders. Take codeine phosphate in the mortar, and triturate, adding the lactose in progressively
increasing portions. Weigh out 200 mg into each of 10 packets and dispense in a neatly labeled envelope.
Prescription No 6
Rx Hyoscinae Hydrobromidi – gr 1/150 Fiat pulvis : Mitte duodecim. Signa : Capiat Unum bis in die
Translation:
Rx Hyoscine hydrobromide -- 0.4mg Prepare a powder. Send 12 powders Label : Take one twice a day.
Calculations in Imperial System:
Calculations for 15 powders : 15 powders should weigh 30 grains. Take 1gr (60mg) of Hyoscine hydrobromide and thoroughly mix with 9gr of lactose. 1gr of this mixture(I) contains 1/10 th grain of Hyoscine hydrobromide. Take 1gr of I and mix with 29gr of lactose. After thorough mixture, 1gr of this contains 1/10*1/30=1/300th gr of Hyoscine hydrobromide and 2gr contain (1/300)*2=1/150th grain of Hyoscine hydrobromide. Weight of one powder is 120 mg.
Calculations in Metric System:
100mg is the minimum that can be weighed and 200mg is the minimum to be dispensend. Take 100mg of hyoscine hydrobromide and mix with 900mg of lactose (I). (b) 100mg of I contains 10mg of Hyoscine hydrobromide; mix 100mg of I with 4,900mg of lactose. Now 500mg contain 10mg ? contain 0.4mg 5000x0.4 = 200mg
Weight of one powder is 200 mg.
Principle: Hyoscine hydrobromide is a very potent substance. It should be double diluted for dispensing.
Procedure:
- As per the calculations above , take 100 mg of Hyoscine hydrobromide and mix with 900 mg of lactose. This is mixture I.
- Take 100 mg of mixture I and mix with 4900 mg of Lactose. This is mixture II.
- Weigh out 200 mg of mixture II into 12 packs.
- Put the packs in a neatly labeled envelope and dispense.
Prescription No 7
Rx Creosote – m ss Lactose – q.s Mitte tales six. Signa : Unum nocte sumendum.
Translation:
Rx Creosote – = 0.03ml Lactose – enough Send six powders. Label : Take one at night.
Weight of each powder is determined by weighing the final powder after mixing Creosote with Lactose.
Principle: Creosote is a liquid. The doctor wants it to be given as a powder. So it should to be incorporated into a solid
like Lactose.
Procedure:
- Proceed for 8 powders 8x0.03 = 0.24ml
- Take 0.24ml of creosote into a small amount of lactose in a glass mortar.
Triturate, adding lactose until a free flowing powder is obtained (All the liquid must be incorporated in it.)
- Transfer onto a piece of butter paper and find the weight of the powder.
- Divide the weight by 8 to get the weight of a single powder. Weigh out six such powders, double wrap and dispense in a neatly labeled envelope.
Prescription No 8
Rx
Send zi of boric acid containing 1% w/w iodine (8% w/v of alcoholic iodine solution is provided). Label : Apply on the affected part.
Calculations:
Boric Acid – 4g 100 grams of the bulk powder should contain 1 gram of iodine. g should contain 8g of iodine is contained in 100ml 0.04g iodine is contained ?
Weight of the bulk powder ( single packet) is 4 g.
Principle: Alcoholic solution of Iodine should be incorporated into Boric acid.
Procedure:
- Take Boric Acid into a glass mortar( because Iodine forms a stain on a porcelein mortar which cannot be removed easily), add 0.5ml of the alcoholic solution of iodine to it, and triturate till there is a dry powder. All the alcohol should evaporate, till then trituration should be done.
- Double wrap and dispense as a single packet.
Prescription No 9
Rx. Sodii Bicarbonatis – gr x Rhei Pulverati – gr iii Olei Menthae Piperitae – mss Fiat pulvis : Mitte novem. Signentur : Unus e cyatho vinoso aquae post cibos quoties opus sit capiendus.
Translation:
Sodium Bicarbonate – 600 mg Powdered rhubarb -- 180 mg Oil of Peppermint -- 0.03 ml Prepare a powder. Send 9 powders. Label: When necessary, take daily, one, with a wine glass of water after meals.
Principle:
The prescribed amounts yield a powder weighing between 13 and 14 grains, hence adjustment to 14grains with lactose will be suitable.
The formula for 10 powders will be
Sodium Bicarbonate – 100gr Powdered Rhubarb – 30gr Oil of Peppermint – 5 minims Lactose – to 140gr
In Metric System: For 10 powders
Sodium bicarbonate – 6000 mg Powdered Rhubarb -- 1800 mg Oil of Peppermint -- 0.3 ml Lactose ---- to 8000 mg
Powdered Rhubarb is a plant material. Plant materials are often supplied as coarse materials. Rhubarb powder should be finely
powdered before it is included in the prescription.
Procedure: After admixture of the first three ingredients, transfer the whole of the material to a scale, add lactose to produce 8000 mg , return to the glass mortar and mix thoroughly, double wrap and dispense as divided powders in a neatly labeled envelope..
Prescription No 10
Rx Zinc Oxide – z ss Calamine – gr xx Starch – z i Fiat pulvis subtitis : Mitte z i Signa : Pulvis conspensus. Apply three times a day.
Translation:
Rx Zinc oxide – 2 g Calamine -- 1200 mg Starch -- up to 32 g Prepare a fine powder. Send 4 g. Label: The Dusting Powder. Apply three times a day.
Principle:
This is a dusting Powder. So there should not be any coarse or gritty particles. It should be triturated into a fine powder.
Procedure:
Take the ingredients into a mortar , finely powder them, mix them thoroughly and dispense as a single packet in a neatly labeled
envelope.
Prescription No 11
Rx Salicylic Acid – 0.05g Benzoic Acid – 0.06g Camphor – 0.01g Menthol – 0.02g Phenol – 0.01g Starch – 1g Mix and send 10g.
Signa : Sprinkle between toes.
Principle:
Camphor, menthol and phenol are separately solids at room temperature. But if any two of these three are mixed in a mortar they will form a liquid, this is known as eutectic formation.
Procedure: This problem of eutectic formation is overcome like this: Take the three eutectic forming liquids into a mortar
and mix; eutectic formation will be there; now incorporate this liquid in the starch, add the other ingredients and mix
thoroughly. Double wrap and dispense as a single bulk powder in a neatly labelled envelope.
Prescription No 12
Rx Benzoic Acid – 1g Zinc Oxide – z ss Mix : Label : Dusting powder Signa : To be applied to face and neck frequently.
Principle: This is a bulk powder containing two white powders; a drop of amaranth solution should be added to the powder
to ascertain thorough mixing.
Procedure: Take the ingredients into a mortar , add a drop of amaranth solution and mix thoroughly. Dispense as a bulk
powder in a single pack in a neatly labeled envelope.
Prescription No 13
Rx Sodium Potassium tartarate – 7.5grams Sodium bicarbonate – 7.5grams Tartaric Acid – 25g Supply in two packets. Signa : Dissolve powder (i) in a glass of water and then add powder (ii), stir and take the liquid while effervescing.
Priciple: Sodium bicarbonate reacts with tartaric acid and gives off effervescense.
Procedure: Sodium potassium tartarate and sodium bicarbonate should be kept in one pack. Tartaric Acid should be kept in a
second pack. Both of them should be kept in an envelope and dispensed with proper directions on the label.
Prescription No 14
Rx Heavy Magnesium Carbonate – 325mg Light Magnesium Carbonate – 325mg Rhubarb powder - 250mg Sugar - 100mg Mix. Take 1 teaspoonful of powder at night.
Principle: Large doses of light substances are prescribed in this prescription. So the ingredients are taken in geometric dilution method and mixed thoroughly. Powder Rhubarb thoroughly if it is coarse.
Author
This article is contributed by Smt. Prof. Jayanti Vijaya Ratna .
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