Bulk Powders and Dusting Powders: The Practical
8 minute read
What you will learn
- Distinguish bulk powders for internal use from dusting powders
- Say which drugs can safely be supplied as bulk powders
- Make a powder by reducing particle size, sieving and mixing in the correct order
- Scale a formula and work out the quantity to supply
- Pack and label each type correctly
- Recognise common faults and how to avoid them
Key points
- A bulk powder for internal use is supplied in one container, and the patient measures each dose. It is only suitable for drugs that are not potent.
- A dusting powder is a fine powder for the skin. It is never to be swallowed.
- Powder the ingredients finely, sieve them, and mix them well. Mix in the same way each time.
- Dusting powders are packed in a container with a sifter top and labelled 'For external use only'.
- Dusting powders for broken skin or open wounds must be sterile.
- Scale every ingredient by the same factor, and check that the parts add up to the total.
- Weighing, mixing and cleaning must be done carefully because powders are dusty.
Two kinds of powder
| Bulk powder for internal use | Dusting powder | |
|---|---|---|
| Route | By mouth | On the skin |
| How supplied | One container. The patient measures each dose with a spoon | A container with a sifter top |
| Examples | Antacid powders, such as magnesium trisilicate compound powder | Talc, starch and zinc oxide powders |
| Particle size | Fine enough to mix and measure | Very fine and smooth, so they do not scratch the skin |
For the theory, including divided powders, see the lesson on powders and granules in BDT 152.
Bulk powders for internal use
A bulk powder is not divided into doses by the dispenser. The patient measures each dose, usually with a 5 mL spoon, and takes it with water or mixes it into water.
Because the patient measures the dose, a bulk powder is only suitable for drugs that are not potent, where a small error does no harm, such as antacids. A potent drug is given as divided powders in individual papers, or as another form.
Dusting powders
A dusting powder is a fine, free-flowing powder applied to the skin to absorb moisture, reduce friction or soothe. The usual bases are talc, starch and zinc oxide.
- A dusting powder is never swallowed.
- It should be very fine, and it is sieved to remove grit.
- A powder used on open wounds or broken skin must be sterile. Ordinary dusting powders should not be put on open wounds.
- Do not use a dusting powder on a baby's skin near the face, as breathing in the dust can harm the lungs.
Method
- Calculate the quantities for the amount ordered and have them checked.
- Weigh each ingredient on a clean boat or paper.
- Powder each ingredient in a mortar if it is coarse.
- Sieve each powder through a fine sieve, to remove lumps and grit.
- Mix them, starting with the smallest quantity and adding the larger quantities in turn. This is geometric dilution, which gives an even mixture.
- Sieve the mixture again to blend it.
- Pack it into the container.
- Label it, and record the preparation.
Work in a clean place, and avoid creating dust. Wipe the balance and the bench afterwards.
Worked examples
Illustrative practice formula, not a pharmacopoeial one.
Scaling. Dusting powder, 100 g: zinc oxide 10 g, starch 40 g, talc 50 g. Make 30 g.
- Scale factor = 30 ÷ 100 = 0.3
- Zinc oxide = 10 × 0.3 = 3 g
- Starch = 40 × 0.3 = 12 g
- Talc = 50 × 0.3 = 15 g
- Check: 3 + 12 + 15 = 30 g, so the parts add up to the total.
Quantity of bulk powder. The dose is 3 g three times a day for 7 days.
- 3 × 3 × 7 = 63 g
Number of doses. A jar holds 63 g and each dose is 3 g.
- 63 ÷ 3 = 21 doses
Packing and labelling
Bulk powder
- Pack in a wide-mouthed, airtight, dry jar, because many powders absorb moisture.
- Label with the name, the dose and how to take it, the date and the patient's name. Supply a 5 mL measuring spoon.
Dusting powder
- Pack in a sifter-top container, such as a plastic or metal shaker.
- Label "For external use only", and the directions, such as "Dust lightly on the affected area after washing and drying".
Faults and what to do
| Fault | Cause | What to do |
|---|---|---|
| Uneven colour or lumps | Poor mixing, or damp powder | Mix again by geometric dilution and sieve |
| Gritty feel | Coarse powder or no sieving | Powder and sieve it again |
| Powder caked in the jar | Moisture got in | Use a dry jar with a tight lid, and keep it cool and dry |
| Dust in the air | Careless pouring | Handle gently, and keep the face away from the dust |
Safety
- Powders are dusty. Do not inhale them, and keep the area clean.
- Check the ingredients against the formula twice before weighing.
- Never supply a potent drug as a bulk powder. Ask the pharmacist.
Exam focus
- Distinguish bulk powders from divided powders, and give an example of each.
- Describe the method for making a dusting powder.
- State the label wording for a dusting powder.
- Common mistake: supplying a potent drug as a bulk powder, where the patient has to measure the dose.
Quick check
Test yourself before you move on. Pick an answer to see the explanation.
1.Which of these can safely be supplied as a bulk powder for internal use?
2.A dusting powder is best packed in:
3.A formula for 100 g of dusting powder has zinc oxide 10 g, starch 40 g and talc 50 g. How much of each is needed for 30 g?
4.Which label wording belongs on a dusting powder?
5.A bulk powder is to be taken as 3 g three times a day for 7 days. What quantity is supplied?