Reconstitution of Powders: The Practical

Why powders for reconstitution?

Many drugs, including many antibiotics, are unstable in water. In a ready-made liquid they would lose strength within days. So the manufacturer supplies them as a dry powder or granules in a bottle. The pharmacy adds water just before supply, which gives a liquid that is good for a limited time. Children and others who cannot swallow tablets benefit most.

Before reconstitution the product has a long shelf life, shown by the expiry date on the bottle. After reconstitution it has a short shelf life, shown by the discard date you put on the label.

Equipment and water

• A clean measuring cylinder (or the mark on the bottle)
• A funnel, if needed
• Purified water, or water that was boiled and cooled, as the manufacturer directs. Tap water can carry germs and chemicals.
• A label, a measuring spoon or an oral syringe, and a pen

Wash your hands and clean the bench before you begin.

Method

1. Read the label: the volume of water, the way of mixing, the storage and the shelf life after mixing. Follow it exactly.
2. Check the product name, the strength and the expiry date of the powder. Do not use it if it has expired.
3. Tap the bottle gently on the bench, or shake it, to loosen the powder.
4. Add the water as directed. Many products say to add the water in two parts, shaking after each, which mixes the powder better.
5. Shake well until the powder is completely mixed, with no lumps.
6. Top up with water to the mark on the bottle if the label says so, and shake again.
7. Label the bottle, with the date and the discard date.
8. Record the reconstitution, and let the pharmacist check it.

Always measure the water with care. If the volume is wrong, the strength of every dose is wrong.

Worked examples

Dose volume. Strength 125 mg in 5 mL. The dose is 250 mg.

• Volume = 250 ÷ 125 × 5 = 10 mL

Quantity to supply. The dose is 10 mL three times a day for 5 days.

• 10 × 3 × 5 = 150 mL

Number of bottles. Each bottle makes 100 mL.

• 150 mL needs 2 bottles, since one bottle gives only 100 mL. The pharmacist decides how to supply a quantity that is not a whole bottle.

A dose by body weight. A child weighs 20 kg. The dose is 10 mg per kg. The strength is 125 mg in 5 mL.

1. Dose = 10 × 20 = 200 mg
2. Volume = 200 ÷ 125 × 5 = 8 mL

Doses by body weight are always set by the prescriber, and checked by the pharmacist. These numbers are for practice.

Discard date. Reconstituted on 4 October. Shelf life 7 days, with the day of reconstitution as day 0.

• 4 + 7 = 11 October

The shelf life after reconstitution, and whether to keep the bottle in a refrigerator, come from the manufacturer's label. Do not use a fixed number from memory.

Labelling and advice

The label of a reconstituted medicine shows:

• the patient's name, the name and strength of the medicine, and the dose;
• the date of reconstitution and the discard date;
• "Shake the bottle well before use";
• the storage advice, such as "Store in a refrigerator" if the label says so;
• any other advice, such as "Finish the course".

Tell the patient to:

• shake the bottle before each dose;
• use the measuring spoon or oral syringe, not a kitchen spoon;
• finish the whole course, even if the child feels better, unless a doctor says otherwise;
• throw away what is left after the discard date;
• keep the bottle out of the reach of children.

Common errors

Safety and records

• Check the product against the prescription before you begin.
• Record the batch number and expiry date of the powder, the date of reconstitution and the discard date.
• Allergies matter, so ask the pharmacist to check, particularly for penicillin-type antibiotics.