accuracy checking course

Accuracy Checking Course For Pharmacy Technicians

Module 5 Version 3: December 2013

Copyright Buttercups Training Ltd

Module 5 – Calculations

Introduction ................................................................................................................ 2 Quantity to be Dispensed ................................................................................................ 2 Units of Mass ............................................................................................................... 2 Units of Volume ............................................................................................................ 2 Determinations of weights and volumes from standard formulae ................................................ 2 Concentrations and Percentages ....................................................................................... 2 Dilutions ..................................................................................................................... 2 Triturations ................................................................................................................. 2 Isotonic And Molar Solutions ............................................................................................. 2 Proportional calculations related to age and weight of patient or both ........................................ 2 Answers to Self-Assessment Questions ................................................................................ 2

Calculate the quantity to be dispensed from daily dosage and duration of treatment

State the units of mass used in the pharmacy using the International System of Units (SI) and state the

relationship between these units

State the units of volume used in the pharmacy using the International System of Units (SI) and state

the relationship between these units

Work out weights of ingredients for different mixtures using a standard formula

Work out volumes of ingredients for different mixtures using a standard formula

State the units of concentration used in the pharmacy

Work out quantities of ingredients from standard formulae

Define different percentage types

%w/w weight in weight solutions and solids

%w/v weight in volume solutions

%v/v volume in volume

Define the meaning of parts in solution

Convert parts to percentages

Use dilution factors to work out how to prepare given percentage concentrations

Define a mole

Define an isotonic solution

Calculate the dosage for a child given its weight and recommended dose/kg

Calculate the dosage for a child given the recommended daily dosage and the age of the child

Contents

By the end of this section you will be able to:





You will already have studied calculations when you completed your technician’s qualification so this

module is designed as a refresher and does not cover basic maths. If you feel that you would benefit from

some tuition on algebra, decimals and fractions then look at the resources available on your course

website.

In this module we will remind you how to work out common calculations that you may come across when

completing an accuracy check on a prescription.

Let us imagine you have this prescription to be dispensed.

What happens if you need to dispense this prescription?

I am sure you find that you are calculating the numbers of tablets required frequently. Prescribers often

tell you how many months’ supply they require by stating it as x/12 where x is the number of months’

supply required.

Of course the maths is slightly more difficult when the calculation involves liquids.

Introduction

Quantity to be Dispensed

Ibuprofen Tablets 200mg tds (28 days)

How many tablets do you need to dispense? Yes, 84 as you need 3 tablets for 28 days.

Rifampicin 150mg capsules

300mg tds (30 days)

You need to dispense 300 divided by 150 multiplied by 3 to give number of capsules required for ONE

day i.e. Two capsules three times a day = 6 capsules

The prescription requires 30 days’ supply so number of capsules dispensed should be 6 x 30 =180

How many tablets do you need to dispense? Yes, 84 as you need 3 tablets for 28 days.





Imagine you have a script for:

Complete these examples and check your answers at the end of the module before moving on.

Good - let us move on...

to something a little more tricky.

Amoxicillin syrup 125mg/5ml

125mg tds 10/7 days

How many doses do you require? You need three doses a day for 10 days or 30 doses.

Each dose is contained in 5ml

So the volume required is 30 x 5 = 150ml

The product is packed in 100ml bottles. The script should therefore be endorsed 2 x 100ml claimed.

So, if you had to take half a tablet for 7 days a community pharmacy would dispense 3

tablets and a half tablets. In hospital nurses may discard half a tablet so halves are

sometimes dispensed as full tablets, i.e. 7 tablets would be dispensed. Find out the policy

if you work in a hospital.

28 days’ supply amoxicillin 250mg caps TDS

Quantity supplied =

28 days’ supply amitriptyline 50mg tabs i tds et ii nocte

Quantity supplied =

28 days’ supply prednisolone 5mg tabs one tablet to be taken daily / one and a half tablets to

be taken on alternate days

Quantity supplied =





The base unit for mass is the kilogram (kg). The units of mass are:

Name Abbreviation Equivalent

1 kilogram kg 1000 g

1 gram g 1000 mg

1 milligram mg 1000 (mcg) g

1 microgram g - use micrograms 1000 ng

1 nanogram ng- use nanograms 1000 picograms

In order to avoid confusion it is better to write the units in full. Quantities should also be written as full

numbers e.g. 100mg not 0.1g. If you do need to use a decimal point make sure that the zero is put in front

of the decimal point to reduce risk of error.

Units of Mass

Can you state 0.05mg in full units?

Multiplying by 1000 gives the answer in micrograms

0.05mg = 50micrograms

Try these and check your answers at the end of the module.

a) 0.05g = ……………………………………………………………………………………………………….…………………………………

b) 0.006g = …………………………………………………………………………………………………………………………………………

c) 0.5mg = …………………………………………………………………………………………………………………………………………

d) 0.05mg = …………………………………………………………………………………………………………………………………………

e) 0.5micrograms = …………………………………………………………………………………………………………………………………





The use of the litre is not actually part of the SI units but its use is not likely to discontinue.

Name Abbreviation Equivalent

1 litre l 1000ml

1 millilitre ml 1000l

1 microlitre l 1/1000ml

I cannot stress too strongly how important this section is. Unfortunately patients lose their lives because of

calculation errors. Use the following sequence always.

Write down the calculation including the units

Work through the calculation step by step

Simplify where possible

Write clearly

Check using a different method if possible

Get someone else to check if possible

Units of Volume

Can you convert the following?

a) 2.5l to ml = ………………………………………………………………………………………………………………………………………

b) 2.5ml to l = …………………………………………………………………………………………………………………….………………

c) 0.5l to ml = ………………………………………………………………………………………………………………………………………

d) 0.375l to ml = ……………………………………………………………………………………………………………………………………

Determinations of weights and volumes from standard formulae





Example 1

Calculate the amounts of the ingredients for 300ml Opiate Squill Linctus BP 1988 and fill in the gaps.

E.g. For Tolu syrup Quantity required =300 x 300 =100ml

900

Now work out the amount required for the other two ingredients.

Example 2

Calculate the quantities required for making 500ml of Chloral Mixture BP 1988

Quantity of Chloral Hydrate required = 1 x 500 = ?

10

Quantity of syrup required:

You will need this to use this formula:

Ingredients Master formula from BP Quantity required

Squill Oxymel 300ml

Camphorated Opium tincture 300ml

Tolu Syrup 300ml

Total volume 900ml 300ml

Ingredients Master formula from BNF Required quantities

Chloral Hydrate 1 g

Syrup 2 ml

Water to 10ml To 500ml

Complete the two examples and check your answers at the end of this module.

Original quantity of ingredient x Total Quantity required = Quantity of ingredient required

Original total quantity





Concentration of substances can be expressed in many different ways, For example:

grams per litre (g/l)

milligrams per litre (mg/l)

milligrams per ml (mg/ml)

grams per ml (g/ml)

moles per litre (mol/l)

parts (1 in 200)

Percentages (X%)

Take 100 Quality Sweet chocolates. 3 of them are the lovely nutty ones wrapped in purple. So 3%

are purple. If I take a chocolate at random 97% will not be the one I want.

You can also express this as a fraction:

But...

Concentration is a way of expressing the strength of a substance; it will be constant no matter what volume

of a substance you take. For example, if you had a morphine sulphate solution 10mg per 5ml you could take

5mls or 100mls of the solution but it would still be the same strength which is 10mg per 5ml (also expressed

as 10mg/5ml).

The latter two we will look at in more detail shortly.

Generally, the concentrations of drugs are expressed as g/l, mg/l or as a percentage. The exception is

concentrations of solutions for injections which are often expressed as mol/l. There should be a prize for

anyone remembering what a molar solution is... can you? Look back on it in your Technician’s training

course or check on the internet; we will return to it shortly.

A percentage is simply a proportion and is expressed using the symbol %. Percent means how many parts in

a hundred.

Concentrations and Percentages

Concentrations

Percentages

3

100

are purple

(we say this as 3 out of 100)

97

100

Are not!





Example 1

The rule to convert a fraction to a percentage is simple - Multiply the fraction by 100

5 x 100 = 7.142%

70

Always remember that the number under the line is the number you use to divide by.

Of course it is very easy to work out percentages when the “out of number” is 100.

Let us imagine that we have 70 chocolates and 5 turn out to be purple. What percentage is purple and

what percentage is not?

As a fraction 5 (5 out of 70) are purple

70

Say you have 20 children coming to a party. 50% of these children want purple chocolates.

How many children want purple chocolates?

You need to express 50% as a fraction: 50

100

then multiply it by the number of children: 50 x 20 = 10 children want purple chocolates.

100

Now you have reminded yourself about fractions and percentages we can proceed. Let us relate this to

pharmacy.

You are asked to produce the following

cream:

Salicylic Acid 5%

Sulphur 3%

White soft paraffin to 100g

The rule is: Amount required =fraction x

total required

Quantity of salicylic acid required is 5%

which is:

5 x Quantity required (100g) = 5g

100

Quantity of Sulphur required is 3% which is:

3 x 100 = 3g

100

Quantity of white soft paraffin (WSP) is

100- (5+3) = 92g

It is a common error to use 100g of the

WSP. Remember that you are making it up

in this case to 100g and if you added 100g

of WSP you would end up with a total

weight of ointment of 108g.

(This is different to making up a liquid

volume that we talked about previously)


Module 5 Version 4: May 2014



Do these calculations again assuming 150g were ordered not 100g.

Quantity of salicylic acid: …………………………………………………….

Quantity of sulphur………………………………………………………………

Quantity of WSP……………………………………………………………………

Answers at the end of the module. Carry on when you are satisfied that you can do this calculation.

The rule is:

Amount required = percentage x total required

Whenever you forget the rule you can work it out by substituting simple numbers.

You know that a 1% salicylic acid ointment in 200g requires 2g salicylic acid so answer was

Amount required = 1 x 200 = 2

100

% w/w shows the weight in mass required in 100g of the product

Calculate the quantity required to make 100g of Syrup BP where sucrose is 66.7% w/w to 100% with freshly

boiled Purified Water.

The quantity required of sucrose is 66.7g made up to 100g with water. The volume will not be 100ml

because the sucrose is denser than water. If you were to make it up to 100ml then you would have too

much water and the syrup solution would be too weak.

Calculate the following:

the quantities required to make 75g of Coal Tar Ointment

Ingredients %w/w for 75g

coal tar solution 12%

hydrous wool fat 12%

yellow soft paraffin 76%

Ie. For hydrous wool fat 12% of 75 is 12 x 75 = 9g

100

Work out the ingredient quantities including the weight required of yellow soft paraffin. If you tried to just

top up to 75g this would be very messy and inconvenient.

Percentage Weight in Weight





This is the number of grams per 100ml of the product.

Calculate the quantity of sodium chloride required to make 50ml of Normal Saline BP

Ingredients %w/v for 50ml

sodium chloride 0.9%

Purified Water to 100%

This is the number of mls of ingredient in 100mls of product.

Calculate the amounts of ingredients required to prepare 200ml Formaldehyde Lotion

Ingredients %v/v for 200ml

Formaldehyde solution 3%

Water to 100%

Check your answers at the end of the module.

Ratios are a way of expressing the proportions of parts or ingredients. The most common examples we use

in everyday life are food recipes.

For example to make pastry you use 1 part of fat to 2 parts of flour.

Let look at how this can be represented

1 Part : 2 Parts or 1 : 2

The colon (:) means “to” so we would read this as 1 part to 2 parts

Percentage Weight in Volume

Percentage Volume in Volume

Dilutions

Ratios





You can also represent this as a pie chart

What is clearer from the pie chart is that you have 3 parts in total, so you can also say that there is 1 in 3

parts of fat.

Summary 1:2 is the same as 1 in 3 (just expressed in different ways)

You may see solutions written as parts e.g. 1 in 8000. For solids in liquids this means parts in grams to

parts in mls of liquid of the FINAL solution.

We all know about dilutions - gin and tonic, orange squash, washing up liquid etc! You take a concentrated

substance and you make it weaker (more dilute).

My orange squash tells me to dilute one part with four parts of water. If we were to make up the squash

then is it a dilution of:

One in Four (1:3-ONE TO THREE) or One in Five (1:4 ONE TO FOUR)

If you look at the 2 cakes below you can see that it makes quite a difference.

Fat

Flour

Flour

1 In 4 1 In 5

Dilutions





Example

So, if you were asked to make 100ml of a 1 in 10 dilution of orange syrup how much orange syrup would

you use?

Answer: 1 in 10 is 10 parts in total

1 in ten equals 100/10 = 10ml

So you would need to take 10mls of the orange syrup and add 90mls of the diluents to make 100ml of

the final strength of the solution

I hope you all you realised that the orange squash was represented as 1:4 (one part of orange squash TO

four parts of water or one part of orange IN five parts)

In dispensing you have to know exactly how much of a substance needs to be mixed with an exact quantity

of something to dilute it - known as the diluent.

So how do we calculate how much of the concentrate we need?

There are two main methods which are used in practice, the dilution factor or a formula.

This is a two stage process, first of all you work out the dilution factor – this is basically how many times

stronger the concentrated solution is compared the diluted solution you make.

Once you know this you can then calculate the amount required to make the diluted solution.

Note: To calculate the dilution factor you must have the percentage strength of each solution to start with.

Dilution Factor Method





Question 1

You are required to make 10mls of a 0.5% solution of sodium chloride and your stock (concentrated)

solution is 5%. How much of the stock solution will be required for the dilution?

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Now try these examples using the dilution fac

Now try these examples using the dilution factor method:

Example

Calculate the amount of concentrate required to dilute a 1 in 100 solution to make 500mls of a 1 in

4000 solution.

So we know the strength of the concentrate (1 in 100) and the dilute solution (1 in 4000) but these

are expressed as a ratio not a percentage. So let’s now convert them to a percentage.

1 in 100 = 1 X 100 = 1%

100

1 in 4000 = 1 X 100 = 0.025%

4000

Now we can place this in the following formula to work out the dilution factor:

Strength of concentrate = the dilution factor

Strength of dilute solution

So 1 = 40 (dilution factor)

0.025%

The final step is to use the dilution factor to see how much concentrate is required. To do this divide

the final volume by the dilution factor.

Final volume = amount of concentrate required

Dilution factor

So 500ml = 12.5ml of concentrate required

40





Question 2

You are going to make 200mls of potassium permanganate solution 0.001%. Your stock solution is 0.2%

so how much will be required for the dilution?

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You will compare the answers of these two questions with your calculations at the end of the next method.

The following formula is often used: C1 x V1 = C2 x V2

C1 = the strength of the concentrated solution (expressed as a percentage)

V1 = the amount of concentrated solution required (mls)

C2 = the strength of the diluted solution (expressed as a percentage)

V2 = the volume of the dilute solution you are making (mls)

Formula Method





Example

Calculate the amount of concentrate required to dilute a 1 in 100 solution to make 500mls of a 1 in

4000 solution?

We have already calculated this using the dilution factor method so let’s try using this formula and

we should arrive at the same answer!

Again we know the strength of the concentrate (1 in 100) and the dilute solution (1 in 4000) but these

are expressed as a ratio not a percentage. So let’s now convert them to a percentage.

1 in 100 = 1 X 100 = 1%

100

1 in 4000 = 1 X 100 = 0.025%

4000

Using the formula: C1 x V1 = C2 x V2

We add the strengths into the equation and the volume of the dilute solution (final volume)

1 x V1 = 0.025 x 500ml

1 x V1 = 12.5

V1 = 12.5 (Remember when you multiply on one side of the equation by 1 then

1 to move it to the other side of the equation you divide by 1)

V1 = 12.5ml volume of concentrate required.

This answers works out the same as the last method so the answer is correct





Question 1

You are required to make 10mls of a 0.5% solution of sodium chloride and your stock (concentrated)

solution is 5%. How much of the stock solution will be required for the dilution?

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Question 2

You are going to make 200mls of potassium permanganate solution 0.001%. Your stock solution is 0.2%

so how much will be required for the dilution?

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Now try these questions again using the formula and see if you get the same answer as the dilution factor

method above

Now you have mastered simple dilutions let’s try to work out a more complicated example!

Send 200ml of potassium permanganate solution which can be made into a 1 in 8000 solution when diluted

with 7 parts of water. How much potassium permanganate will be required to make up the 200ml solution?

So we know that 1 part of concentrated solution mixed with 7 parts of water gives 1 in 8000

Step 1 Convert 1 in 8000 to a %

1/8000 x 100 = 0.0125%

We know the dilution factor is 8 (1 part to 7 parts is 1 part IN 8 parts)

Step 2 Write down the calculation

Dilution factor = strength of concentrate

strength of dilution





Summary

learn the formula

write down the details you know

convert any fractions to percentages by multiplying by 100

do the calculations both ways to double check your answers

Question 1

Calculate the quantity of potassium permanganate required to prepare 300ml of a 1 in 1000 solution

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Remember a 0.1% solution means 0.1 g in 100ml

So if we are sending 200ml of a 0.1% solution it will contain 0.2g in 200ml.

You need 0.2g of potassium permanganate.

Best of luck! Try the following.....

Step 3 Put in amounts that you know

8 = Strength of concentrate

0.0125%

Step 4 Rearrange calculation to give missing amount

8 x 0.0125 = strength of concentrate

Strength of concentrate = 0.1%





Question 2

Give dilution directions for preparing 200ml quantities of a 1 in 4000 solution from 1 in 1000

Strength of concentrate = 1 in 1000

Strength of dilution = 1 in 4000

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Question 3

Calculate the amount of concentrated cinnamon water required to prepare 300ml of cinnamon water

BP. Cinnamon water is prepared from concentrated cinnamon water by diluting 1 part of concentrate

with 39 parts of water.

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Question 4

You need to send 100ml of potassium permanganate solution which can be made into a 1 in 2000

solution when diluted with 5 parts of water. Calculate how much potassium permanganate will be

required.

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Question 5

Give directions to dilute a 0.25% solution of potassium permanganate to make 500ml of a 1 in 5000

solution.

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If you needed to dilute an active solid powder with an inert diluent in order to obtain smaller quantities of

the active ingredient this is called ‘trituration’.

You are asked to make a solution of 40mg of Diamorphine hydrochloride in 100ml of chloroform water. This

is too small a quantity to weigh accurately; you can only measure 100mg accurately!

So 100mg is weighed and is then dissolved in 10ml of diluent and you have a solution of 100mg/10ml. BUT

you only require 40mg.

1mg is contained in 10ml

100

40mg is contained in 10 x 40 = 4ml

100

If the diluent (sometimes known as a vehicle) is unsuitable such as syrup or glycerin then there are two

other alternatives:

make up an excess

dissolve in water first

Note: for solutions of w/w then the trituration can still be done but the liquid must be weighed not

measured.

Triturations





Have you found out what a Molar solution is?

We cannot weigh or count individual atoms. We could if we weighed out a huge number. Chemists have

chosen to call this number the Avogadro Number.

The number is 6 X 10 23

We call this 10 to the power 23. It means 10 X 10 (23 times).....or 1 followed by 23 zeros.

An amount of a substance containing this huge number of particles is called a mole.

The relative atomic mass of a substance is the sum of its numbers of protons and neutrons. We say that

this number expressed in grams contains a mole of the substance. You cannot work out atomic mass from

the number as you do not know how many neutrons are present in the element.

Iron (Fe) contains 26 protons and 30 neutrons thus its relative atomic mass is 56

We say that 56g of iron contains 1 Mole (mol)

Water (H20) has a molecular weight of 1 + 1 + 16 = 18 ie. The total of the atomic weights of its atoms

1 Mole of water weighs 18g

Chemists and pharmacists often need to express the strength of a solution. They may express it as Moles

per litre.

Example

Make up a solution of 30mg diamorphine hydrochloride in 25ml chloroform water. 100mg is the

minimum weighable quantity.

Weigh 100mg then dissolve in 10ml of chloroform water to give 100mg/10ml

100mg per 10ml means that there is 10mg per 1ml

You only need 30mg so take 3ml of the solution

This 3ml is then diluted with more chloroform water to make it up to 25 mls

25ml-3ml = 22ml

So 22ml is added to make a final solution which is 30mg in 25mls.

Isotonic And Molar Solutions





What is an isotonic solution?

An isotonic solution is one which is has the same osmotic pressure as another solution. It is important

to bathe body cells in solutions which are isotonic. What happens if you bathe them in a solution of

salt water which is too strong? You may recall that water will come out of the body cells into the

stronger solution by osmosis. We call saline solution which is the same strength as our body cells

Normal Saline.

If you look up doses in the BNF you will find children's doses except where it is not recommended. Many

are based on weight in kilograms or the following age ranges:

First month

up to one year

1-5years

6-12 years

We say that if one mole is dissolved in a litre this is a molar solution (1mol). A molar solution of sodium

chloride would be 23 + 35.5 = 58.5g in 1 litre of water.

All children differ from adults in their response to drugs. Special care is needed for newly born babies

particularly in the neonatal period or first 30 days of life.

The risks of toxicity (poisonous effects) of the drug are increased because of the following:

Enzymes (proteins made in the body which control reactions) required to metabolise (change or get rid

of) the drug may be deficient

The organs particularly the kidneys and liver are not sufficiently developed to deal with excretion and

detoxifying procedures

The weight of the baby is very small

In childhood, doses should be adjusted until the weight reached is 50kg.

Proportional calculations related to age and weight of patient or both





Children's doses may be calculated from adult doses by using age, weight or body surface area or by a

combination.

Body weight

The dose is usually stated as mg / kg ( milligrams per kilogram). This means that the amount of drug (in

mg) is worked out according to the weight of the patient (in kg).

The heavier the patient, the more drug they can be given.

This makes sense if you think about children: usually the older the child, the heavier they will be, so the

more drug they can be given.

Now let's go back to mg / kg.

To work out the dose for the patient you multiply

number of mg x number of kg

Dose Calculation

Example 1

Let's think about this in a simple way first.

We'll make the question: I am allowed to eat 2 chocolate bars per day. How many can I eat per week?

You probably have the answer as 14 (I hope!) - but how did you work it out?

We have 2 bars per day; 7 days per week.

Therefore we multiplied the number of bars by the number of days in a week. 2x7=14

Example 2

A rabbit can eat 2 carrots for every kg it weighs. i.e.. 2 carrots / kg

How many carrots can a 2kg rabbit eat?

How many carrots can a 3kg rabbit eat?

The 2kg rabbit can eat 2x2 = 4 carrots and the 3kg rabbit can eat 2x3 = 6 carrots





Question

What daily dose of erythromycin should be given by intravenous infusion to a 2 year old child weighing

12kg? (Assume the child has a severe infection and the dose is 12.5mg/kg every 6 hours)

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So, if the dose of a drug is 5mg/kg and the child weighs 20kg, the dose for that child is

5 x 20 = 100mg

Example

Look at furosemide in the BNF for children.

The intravenous dose by slow injection for a child aged 7 is 0.5 -1 mg / kg every 8 hours, with a

maximum of 2mg/kg

In other words, the child can be given between 0.5mg and 2mg per kg that they weigh.

If a child weighs 15kg, the daily dose for furosemide is between

0.5 x 15 = 7.5mg

and

2.0 x 15 = 30mg





Age

This is often used as a guideline for children's doses. Always check the age of the child.

Example

Let us try the following prescription for a child aged 8 months for Augmentin 125/31 SF TDS Look up

the dose in the BNF and write here the suggested dosage.

You should have found that the dose is 0.25ml /kg three times a day

The baby weighs 6kg.

Each dose required is therefore 6 x 0.25ml = 1.5ml

This must be given three times a day.

If we needed this dose to be administered as 2.5ml because 1.5ml was too small to be accurately

measured by the mother or carer then a dilution must be made. Let say we are going to make 100mls

of the diluted solution.

So we know that each 2.5ml of the final diluted solution will only contain 1.5ml of the concentrate

solution and the rest will be additional water it has been diluted with.

So what proportion is the concentrate solution?

1.5 X 100 = 60%

2.5

So 60% of 100 is 60ml. Therefore take 6oml of concentrate and top up to 100ml of water. Shake well.

Original dose will then be contained in 2.5ml.





28 days’ supply amoxicillin 250mg caps TDS - Quantity supplied = 84

28 days’ supply amitriptyline 50mg tabs i tds et ii nocte - Quantity supplied = 140

28 days’ supply prednisolone 5mg tabs one tablet to be taken daily / one and a half tablets to be taken

on alternate days - Quantity supplied = 35 (unless in hospital 2 tabs are dispensed on alternative days

giving a total of 42)

a) 0.05g = 50milligrams

b) 0.006g = 6milligrams

c) 0.5mg = 500micrograms

d) 0.05mg = 50micrograms

e) 0.5micrograms = 500nanograms

a) 2.5l to ml = 2500ml

b) 2.5ml to l - 2500l

c) 0.5l to ml = 500ml

d) 0.375l to ml = 375ml

Ingredients Master formula from BP Quantity required

Squill Oxymel 300ml 100ml

Camphorated Opium tincture 300ml 100ml

Tolu Syrup 300ml 100ml

Total volume 900ml 300ml

Ingredients Master formula from BNF Required quantities

Chloral Hydrate 1 g 50g

Syrup 2 ml 100ml

Water to 10ml To 500ml

Answers to Self-Assessment Questions

Page 3

Page 4

Page 5

Page 6





Quantity of salicylic acid (5%) = 7.5g

Quantity of sulphur ( 3%) = 4.5g

Quantity of WSP ( to 100%) = 138g

Ingredients %w/w for 75g

coal tar solution 12% 9g

hydrous wool fat 12% 9g

yellow soft paraffin 76% 57g

Ingredients %w/v for 50ml

sodium chloride 0.9% 0.45g

Purified Water to 100% To 50ml

Ingredients %v/v for 200ml

Formaldehyde solution 3% 6ml

Water to 100% To 200ml

Q1. Calculate the quantity of potassium permanganate required to prepare 300ml of a 1 in 1000 solution:

0.1% solution so 0.3g in 300ml

Q2. Give dilution directions for preparing 200ml quantities of a 1 in 4000 solution from 1 in 1000

Strength of concentrate = 1 in 1000 = 0.1%

Strength of dilution = 1 in 4000 = 0.025%

Dilution factor = 0.1/0.025 = 4

200/4 = 50 ml of concentrate required, topped up to 200ml with diluent.

Q3. Calculate the amount of concentrated cinnamon water required to prepare 300ml of cinnamon water

BP. Cinnamon water is prepared from concentrated cinnamon water by diluting 1 part of concentrate with

39 parts of water.

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300/40 = 7.5ml required

Q4. Send 100ml of potassium permanganate solution which can be made into a 1 in 2000 solution when

diluted with 5 parts of water.

C1 x V1 = C2 x V2

C1 x 100 = 0.05 x 600

C1 = 0.05 x 600 / 100 = 0.3% i.e. 0.3g

Q5. Give directions to dilute a 0.25% solution of potassium permanganate to make 500ml of a 1 in 5000

solution.

1 in 5000 = 1 x 100 = 0.02%

5000

So now use C1 x V1 = C2 x V2

0.25 x V1 = 0.02 x 500

V1 = 0.02 x 500/0.25 = 40ml

So take 40ml of 0.25% solution and top up to 500ml with diluent

What daily dose of erythromycin should be given by intravenous infusion to a 2 year old child weighing

12kg? (Assume the child has a severe infection and the dose is 12.5mg/kg every 6 hours)

12.5 mg x 12 = 150mg to be given every 6 hours

So 300mg to be given in 12 hours

and 600mg to be given in 24 hours

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For each of the following questions select one

answer that you think is most suitable from the 4

options available

1. Convert 68micrograms into milligrams:

a) 6.8mg

b) 0.68mg

c) 0.068mg

d) 0.0068mg

2. Convert 2700micrograms into g:

a) 0.0027g

b) 0.027g

c) 0.27g

d) 2.7g

3. Convert 25 milligrams into grams:

a) 2.5g

b) 0.25g

c) 0.025g

d) 0.0025g

Assessment for module 5

Name:...................................................... Pharmacy Name and Address

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4. Convert 2.6L into millilitres:

a) 2600mL

b) 260mL

c) 26mL

d) 2.6mL

5. A 200ml bottle of medicine contains 800mg of drug Y. What is the strength, as a percentage, of

this preparation?

a) 0.25%

b) 0.4%

c) 25%

d) 4%

6. A cream contains 2% salicylic acid. How much salicylic acid is present in 200g of the cream?

a) 2g

b) 4g

c) 0.1g

d) 20g

7. You have been asked to make 150ml of a 2.5% (W/V) solution of Drug X. How much of the drug

will you need to make this solution?

a) 37.5g

b) 37.5mls

c) 3.75g

d) 3.75mls

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8. A bottle of medicine contains drug Y 2% suspension. The patient requires a 150mg dose of drug Y

twice a day for 14 days. How much do you need to supply?

a) 210ml

b) 21ml

c) 105ml

d) 150ml

9. A prescription states that the patient should "take two tablets BD for 5/7". How many tablets

should be dispensed?

a) 14

b) 20

c) 28

d) 56

10. A patient is prescribed 10mg cetirizine/day. The prescriber has indicated that they should have

the oral liquid which is available as a 5mg/5mL strength. What volume will they need for two

week's treatment?

a) 35mL

b) 70mL

c) 105mL

d) 140mL

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11. The dose of oral propranolol for a neonate with an arrhythmia is 250-500micrograms/kg. It is

available as an oral solution (5mg/5mL).

The prescriber wants to give the patient a starting dose of 300micrograms/kg. The baby weighs

4kg.

What volume of propranolol does the baby need for each dose?

a) 3mL

b) 1.2mL

c) 0.1ml

d) 5mL

12. You have to prepare 500g of the following ointment:

Ingredient Percentage (%) Calculation Quantity to make 500g

Yellow soft paraffin 40

White soft paraffin 40

Emulsifying ointment 20

Select the answer which gives the correct quantities to prepare 500g. (You may find it helpful to

complete the two columns in the table above.)

a) 50g yellow soft paraffin, 50g white soft paraffin, 400g emulsifying ointment

b) 100g yellow soft paraffin, 100g white soft paraffin, 300g emulsifying ointment

c) 200g yellow soft paraffin, 200g white soft paraffin, 100g emulsifying ointment

d) 100g yellow soft paraffin, 200g white soft paraffin, 200g emulsifying ointment

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13. You have a 1 to 5 dilution of Dermovate Ointment in White Soft Paraffin. The total weight of the

jar is 60g. How much Dermovate ointment does this contain?

a) 5g

b) 6g

c) 10g

d) 12g

14. You are supplied with a solution of flucloxacillin 500mg/ml. Complete the formula below for the

preparation of 50ml of a solution containing flucloxacillin 250mg/5ml.

a) 25ml Flucloxacillin 500mg/ml diluted with Water for preparations to 50ml

b) 10ml Flucloxacillin 500mg/ml diluted with Water for preparations to 50ml

c) 20ml Flucloxacillin 500mg/ml diluted with Water for preparations to 50ml

d) 5ml Flucloxacillin 500mg/ml diluted with Water for preparations to 50ml

15. Give dilution instructions for preparing 600ml of a 1 in 8000 solution from a 3 in 5000 solution

(the diluent will be water).

a) Add 225ml of water to 350ml of the 3 in 5000 solution

b) Add 225ml of the 3 in 5000 solution to 350ml of water

c) Add 125ml of the 3 in 5000 solution to 475ml of water

d) Add 125ml of water to 475ml of the 3 in 5000 solution

Photocopy your work before posting it for marking,

Or take the test on-line and get immediate results!

Answer:

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accuracy checking course

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