birth by 10%. When it was born it weighed 3kg.

What is its new weight?

4. A young adult’s height was measured
and found to be 1.3m. They grow by 10% over the
next year. What is their new
height?
5. A patient loses 7% of their body weight
after surgery. If they originally weighed 195 kg
what is their new weight?
For extra help with Percentages consult
Mathematics leaflets ‘Fractions, Decimals
and Percentages: how to link them’ and
‘Percentages’ available on the web at
www.hull.ac.uk/studyadvice
Percentages Exercise 1 - Answers
3. New weight is 3.3kg or 3300g
4. 1.43m
5. 181.35 kg
Percentage increase/decrease
We often need to find the percentage increase or
decrease in a patient’s weight. To do this we use
the formula:
Change in Weight x 100
Original Weight
Example:
A patient who originally weighed 50kg loses 2 kg.
What is her percentage weight loss?
Her change in weight is 2 kg and her original
weight is 50 kg.
So we have 2_ x 100 = 4
50
This represents a 4% weight loss.
A patient who originally weighed 125 kg now
weighs 135 kg. What is his percentage weight
gain?
Here the change in weight is 10 kg and the original
weight is 125 kg.
So that we have 10__ x 100 = 8
125
This represents an 8% weight gain.
28
Percentages Exercise 2
Find the weight gain/loss of the following patients.
a) Weight originally 80 kg, final weight
92 kg
d) Weight originally 200 kg, final weight
195 kg
b) Weight originally 60 kg, final weight
63 kg
e) Weight originally 250 kg, final weight
245 kg
c) Weight originally125 kg, final weight
120 kg
Percentages Exercise 2 – Answers
a)15% weight increase
d) 2.5% weight decrease
b) 5% weight increase
e) 2% weight decrease
c) 4% weight decrease
29
Body Mass Index (BMI)
The BMI provides a simple numeric measure of a
person’s ‘fatness’ or ‘thinness’ which allows
healthcare professionals to discuss over and
underweight problems objectively.
The current settings are:
BMI < 20 – Underweight
20 < BMI < 25 – Optimum weight
25 < BMI < 30 – Overweight
BMI > 30 – Obese
BMI > 40 – Morbidly obese
BMI is calculated by dividing the person’s weight
(in Kg) by their height 2 (in metres).
The formula is written W
H2
Example
Find the BMI of a patient who weighs 75 kg and is
1.42 m tall
BMI = 75 / (1.42 x 1.42) = 34.72
To the nearest whole number this is 35, therefore
this patient is in the obese range.
Find the BMI of a patient who weighs 93 kg and is
1.95m tall
BMI = 93 / (1.95 x 1.95) = 24.46
To the nearest whole number this is 24, therefore
this patient is in the optimum weight range.
Body Mass Index Exercise with answers
Find the BMI of the following patients to the
nearest whole number
a) Weight 80 kg, height 1.83m (24)
b) Weight 115 kg, height 2.00m (29)
c) Weight 78 kg, height 1.54m (33)
d) Weight 62 kg, height 1.8m (19)
e) Weight 132 kg, height 1.64m (49)
30
Averages
The average or the mean of a set of numbers is
just the value you get after adding the set of
numbers up and dividing by how many numbers
you have.
Examples
1. Find the average of 2, 6, 4, 8, 5
2+6+4+8+5 = 25
=5
The average is 5
2. If a patient’s oral fluid intake on successive days
is 120 mL, 200 mL 140 mL and 260 mL, what was
the average intake over 4 days?
120+200+140+260 = 720
= 180
The average intake is 180 mL
Averages Exercise
1. A patient’s pulse was taken every 30 minutes
over 2 hours
It was found to be 110, 105, 95 and 90
What is the average pulse rate over the 2 hours?
2. A patient’s temperature was taken every 30
minutes over 4 hours.
It was 38°C, 38°C, 38.5°C, 39.1°C, 38.4°C,
38.1C°, 37.4°C, and 42.1°C
What is the average temperature over:
a) The first two hours
b) The second two hours
Averages Exercise
1. 100
2. a) 38.4°C b) 39.0°C
31
Unit Conversion
In your chosen field you are likely to need to
convert weights and volumes from one unit to
another.
Metric Measurements of Weight
Name
Abbreviation
Notes
Kilogram
kg
Approx. the weight of a litre of water
Gram
g
One thousand grams to a kilogram
Milligram
mg
One thousand mg to the gram
Microgram
mcg
One million mcg to the gram
Nanogram
ng
One thousand ng to the mcg
Conversion Chart
Number of
Kilograms
Number of Grams
Number of Milligrams
Number of
Micrograms
Number of
Nanograms
x 1000
÷1000
÷1000
÷1000
÷1000
x 1000
x 1000
x 1000
As we move down the diagram the arrows are on
the right and we move the decimal point three
places to the right. As we move up the diagram the
arrows are on the left and we move the decimal
point three places to the left.
32
Metric Measurements of Liquids
Name
Abbreviation
Notes
Litre
L
An upper case L
Millilitre
mL
One thousand millilitres to a litre
Conversion Chart
There is also the centilitre (cL), so named as there
are a hundred of them in a litre.
A single centilitre is equivalent to 10mL. Centilitres
are normally used to measure wine.
DO NOT USE A LOWER CASE L AS AN
ABBREVIATION FOR LITRES. There is a chance
of misreading 3l as thirty one (31) when it should
be 3L. Always use L even in mL!
Examples
1. Convert 575 millilitres into litres.
From the diagram, we see that to convert millilitres
to litres, we divide the number of millilitres by
1000.
So we have 575÷1000=0.575 litres
2. Convert 2.67 litres into millilitres.
To convert litres to millilitres we multiply the
number of litres by 1000.
So we have 2.67×1000=2670 millilitres
Estimation
Always look at the answers you produce to check
they are sensible. A good way to do this is to
estimate the answer.
Number of
Litres
Number of Millilitres
x 1000
÷1000
33
In Example 1 above we can use our knowledge of
litres and millilitres to estimate the result. We have
575 millilitres. If we had 1000 millilitres we would
have a litre. Half a litre would be 500 millilitres, so
our result will be a little over half a litre.
Conversions of lbs ⇾ kg, kg ⇾ lbs
It is sometimes necessary to change from imperial
units to metric units and vice versa. The method is
shown below:
Weights in kg x 2.2 = weights in pounds.
A patient weighs 124 kg, what is this in pounds
(lbs)?
124 x 2.2 = 272.8 lbs
Weights in pounds ÷ 2.2 = weights in kg.
A patient weighs 212 lbs, what is this in kg?
212 ÷ 2.2 = 96.37 (2dp) kg
34
Unit Conversion Exercise 1
1. Copy and complete the following, using the
tables and diagrams
a) 1 kilogram = ____ grams
b) 1 gram = ____ milligrams
c) 1 gram = ____ micrograms
d) 1 microgram = ____ nanograms
e) 1 litre = ____ millilitres
2. Convert the following into milligrams
a) 6 grams b) 26.8 grams c) 3.924 grams d) 405
grams
3. Convert the following into grams
a) 1200mg b) 650mg c) 6749mg d) 3554mg
4. Convert the following into milligrams
a) 120 micrograms b) 1001 micrograms c) 2675
micrograms
d) 12034 mcg
5. Convert the following: (you may find it easier to
work out the answers in two stages):
a) 1.67grams into micrograms b) 0.85grams into
micrograms
c) 125 micrograms into grams d) 6784 micrograms
into grams
e) 48.9 milligrams into nanograms f) 3084
nanograms into milligrams
6. Convert the following into litres
a) 10 millilitres b) 132 millilitres c) 2389 millilitres d)
123.4 millilitres
7. Convert the following into millilitres
a) 4 litres b) 6.2 litres c) 0.94 litres d) 12.27 litres
8. A patient needs a dose of 0.5 g of medicine A.
They have already had 360mg.
a) How many more mg do they need?
b) What is this value in grams?
c) A dose of 1400 mcg has been prepared. Will
this be enough?
35
Unit Conversion Exercise 1 - Answers
1
a) 1kg=1000g
b) 1g=1000mg
c) 1g=1000000mcg
d) 1 mcg=1000ng
e) 1 litre=1000Ml
2
a) 6g=6000mg
b) 268g=26.800mg
c) 3.924g=3924mg
d) 405g=405000mg
3
a) 1200mg=1.2g
b) 650mg=0.65g
c) 6749mg=6.749g
d) 3554mg=3.554g
4
a)120mcg=0.12mg
b) 1001mcg=1.001mg
c)2675 mcg= 2.675mg
d) 12034mcg=12.034mg
5
a) 1.67g=1670000mcg
b) 0.85g=850000mcg
c) 125 mcg=0.000125g
d) 6784mcg=0.006784g
e) 48.9mg=48900000ng
f) 3084ng=0.003084mg
6
a) 10mL=0.01litres
b) 132mL=0.132litres
c) 2389mL=2.389litres
d) 123.4mL=0.1234 litres
7
a) 4litres=4000mL
b) 6.2litres=6200mL
c) 0.94litres=940mL
d) 12.27litres=12270mL
8
a) 140 milligrams
b) 0.14 grams
c) no, the correct dose would be 140000mcg
36
Dosage Calculations
Working out a dosage in either tablets or liquids is
straightforward. The formula used is always the
same.
What you want x What it’s in
What you’ve got
When working with tablets what it’s in is always
one tablet.
To calculate a dosage you must write down 3
numbers.
They are:
What you want – this is what is
prescribed/ordered/required/needed by the patient.
What you have got – this is what is available.
What it’s in – this is either 1 when we are working
with tablets or in mL when working with liquids.
The order in which you write these down is not
difficult to remember, if you think ‘The patient
always comes first’ ie. What you want.
Examples
1. A patient needs 500mg of drug X per day. X is
available in 125mg tablets. How many tablets per
day does he need to take?
What you want = 500mg } The units are both the
same
What you’ve got = 125mg }
What it is in = one tablet
So our calculation is
x1=4
The patient needs 4 tablets a day.
2. We need a dose of 500mg of Y. Y is available in
a solution of 250mg per 50mL.
In this case,
What you want = 500mg } both in mg
Note: In order to use this formula, the units of
‘What you want’ and ‘What you’ve got’ must be the
same, ie. both in mcg, or both in mg, or both in g.
37
What you’ve got = 250mg }
What it’s in = 50mL
So our calculation is
250
500× 50 =100
We need 100mL of solution.
3. We need a dose of 250mg of Z. Z is available in
a solution of 400mg per 200mL.
In this case,
What you want = 250mg } both in mg
What you’ve got = 400mg }
What it’s in = 200mL
So our calculation is
400
250× 200 = 125
We need 125mL of solution.
4. A patient is prescribed 250mg of erythromycin
IV.
Stock on hand contains 1g in 10mL once diluted.
What you want = 250mg
What you’ve got = 1g
What it’s in = 10mL
The units of What you want are mg and the units
of What you’ve got are g. They
must be the same units.
Both in mg
1g = 1000mg
So:
What you want = 250mg
What you’ve got = 1000mg
What it’s in = 10mL
Our calculation is
250 x 10 = 2.5
1000
We need 2.5mL
Both in g
250mg = 0.25g
= 0.25g
=1g
=10mL
Our calculation is
0.25 x 10 = 2.5
1
We need 2.5mL
Medicine over Time
Tablets/liquids
This differs from the normal calculations in that we
have to split our answer for the
total dosage into 2 or more smaller doses.
Example A child weighing 12.5kg is prescribed a
drug which is to be given in four
equally divided doses. The dosage the child
requires is 100mg/kg body weight.
The child requires 12.5 x 100mg = 1250mg of the
drug.
38
So for four equally divided doses
1250 = 312.5
4
They need 312.5mg four times a day.

Drugs delivered via infusion

For calculations involving infusion, we need the
following information:
The total dosage required
The period of time over which medication is to be
given
How much medication there is in the solution
A patient is receiving 500mg of medicine X over a
20 hour period.
X is delivered in a solution of 10mg per 50mL.
What rate should the infusion be set to?
Here our total dosage required is 500mg
Period of time is 20 hours
There are 10mg of X per 50mL of solution
Firstly we need to know the total volume of
solution that the patient is to receive.
Using the formula for liquid dosage we have:
10
500 ×50=2500 so the patient needs to receive
2500mL.
We now divide the amount to be given by the time
to be taken: 20
2500=125
The patient needs 2500mL to be given at a rate of
125mL per hour
Note: Working out medicines over time can
appear daunting, but all you need to do
is work out how much medicine is needed in total,
and then divide it by the amount of
doses needed or the time over which it is to be
given.
Drugs labelled as a percentage
Some drugs may be labelled in different ways from
those used earlier.
V/V and W/V
Some drugs may have V/V or W/V on the label.
V/V means that the percentage on the bottle
corresponds to volume of drug per
volume of solution i.e 15% V/V means for every
100mL of solution, 15mL is the drug.
W/V means that the percentage on the bottle
corresponds to the weight of drug per
volume of solution. Normally this is of the form
‘number of grams per number of
millilitres’. So in this case 15% W/V means that for
every 100mL of solution there are
15 grams of the drug.
39
If we are converting between solution strengths,
such as diluting a 20% solution to
make it a 10% solution, we do not need to know
whether the solution is V/V or W/V.
Examples
1. We need to make up 1 litre of a 5% solution of
A. We have stock solution of 10%.
How much of the stock solution do we need? How
much water do we need?
We can adapt the formula for liquid medicines
here:
What we want × What we want it to be in
What we’ve got
We want a 5% solution. This is the same as 100
5 or 20
1.
We’ve got a 10% solution. This is the same as 100
10 or 10
1.
We want our finished solution to have a volume of
1000mL.
Our formula becomes
10
1
20
1
×1000
= 20
1×1
10 ×1000 (using the rule for dividing fractions)
=2
1 ×1000=500 . We need 500mL of the A solution.
Which means we need 1000-500=500mL of water.
(Alternatively you can use the fact that a 5%
solution is half the strength of a 10%
solution to see that you need 500mL of solution
and 500mL of water)
2. You have a 20% V/V solution of drug F. The
patient requires 30mL of the drug.
How much of the solution is required?
20% V/V means that for every 100mL of solution
we have 20mL of drug F.
Using our formula:
What you want × What it’s in
What you’ve got
This becomes 20
30 ×100=150
We need 150mL of solution.
3. Drug G comes in a W/V solution of 5%. The
patient requires 15 grams of G. How
many mL of solution are needed?
40
5% W/V means that for every 100mL of solution,
there are 5 grams of G.
Using the formula gives us
5
15 ×100=300
300mL of solution are required.
Note In very rare cases, a drug may be labelled
with a ratio. If this is the case, refer
to the Drug Information Sheet for the specific
medication in order to be completely
sure how the solution is made up.
Dosage Calculations Exercise 1
1. How many 30mg tablets of drug B are required
to produce a dosage of:
a) 60mg b) 120mg c) 15mg d) 75mg
2. Medicine A is available in a solution of 10mg per
50mL. How many mL are needed
to produce a dose of:
a) 30mg b) 5mg c) 200mg d) 85mg
3. Medicine C is available in a solution of 15
micrograms per 100mL. How many mL
are needed to produce a dose of:
a)150mcg b) 45mcg c)30mcg d) 75mcg
4. Medicine D comes in 20mg tablets. How many
tablets are required in each dose
for the following situations:
a) total dosage 120mg , 3 doses b) total dosage
60mg, 2 doses
c) total dosage 100mg, 5 doses d) total dosage
30mg, 3 doses
5. At what rate per hour should the following
infusions be set?
a) Total dosage 300mg, solution of 25mg per
100mL, over 12 hours
b) Total dosage 750mg, solution of 10mg per
30mL, over 20 hours
c) Total dosage 450mg, solution of 90mg per
100mL, over 10 hours
6. Drug B comes in a 20% V/V stock solution.
i) How much of the solution is needed to provide:
a) 50mL of B b) 10mL of B c) 200mL of B
ii) How would you make up the following solutions
from the stock solution?
a) Strength 20% volume 1 litre b) Strength 10%
volume 750mL
iii) What strength are the following solutions?
a) Volume 1 litre, made up of 600mL stock
solution, 400mL water
b) Volume 600mL, made up of 300mL stock
solution, 300mL water
7. Drug C comes in a 15% W/V stock solution.
i) How much of the solution is needed to provide:
41
a) 30g of C b) 22.5g of C c) 90g of C
ii) How would you make up the following solutions
from the stock solution?
a) Strength 5% volume 900mL b) Strength 10%
volume 750mL
iii) How many grams of C are in the following
solutions?
a) Volume 1 litre, made up of 400mL stock
solution, 600mL water
b) Volume 800mL, made up of 450mL stock
solution, 350mL water
Dosage Calculations Exercise 1 – Answers
1. a) 2 tablets b) 4 tablets c) 2
1 tablet d)
22
1 tablets
2. a) 150mL b) 25mL c) 1000mL d) 425mL
3. a) 1000mL b) 300mL c) 200mL d) 500mL
4. a) 2 tablets b) 1 2
1 tablets c) 1 tablet d) 2
1 tablet
5. a) 100mL per hour b) 112.5 mL per hour c)
50mL per hour
6. i) a) 250mL b) 50mL c) 1 litre
ii) a) 1 litre stock, no water b) 375mL stock, 375mL
water
iii) a) 600mL stock contains 120mL B
So 120mL in 1000mL= 1000
120 =12%
b) 300mL stock contains 60mL B
So 60mL in 600mL= 600
60 =10%
7. i) a) 200mL b) 150mL c) 600mL
ii) a) 300mL stock, 600mL water b) 500mL stock,
250mL water
iii) a) 60g b) 67.5g
Dosage Calculations Exercise 2
A drug is available in 1 mg, 2 mg, 5 mg and 10 mg
tablets.
What is the best combination of these (i.e. the
smallest number of tablets) to give the
following dosages?
Dosage Tablets required Number of tablets
1 3 mg
2 7 mg
3 8 mg
4 10mg
5 11 mg
42
6
14 mg
Dosage Calculations Exercise 2 – Answers
Tablets required
Number of tablets
Tablets required
Number of tablets
1
1 mg & 2 mg
2
2
2 mg & 5 mg
2
3
1 mg, 2 mg & 5 mg
3
4
5 mg & 5 mg
2
5
5 mg, 5 mg & 1 mg
3
6
5 mg, 5 mg, 2 mg & 2 mg
4
Dosage Calculations Exercise 3
1. A solution contains furosemide (frusemide) 10
mg/mL. How many milligrams of frusemide are in
a 2 mL b 3 mL c 5 mL of the solution?
2. A solution contains morphine hydrochloride 2
mg/mL. How many milligrams of morphine
hydrochloride are in
a 3 mL b 5 mL c 7 mL of the solution?
3. Another solution contains morphine
hydrochloride 40 mg/mL. How many milligrams of
morphine hydrochloride are in
a 2 mL b 5 mL c 10 mL of this solution?
4. A suspension contains phenytoin 125 mg/5 mL.
How many milligrams of phenytoin are in
a 20 mL b 30 mL c 40 mL of the suspension?
43
5. A solution contains fluoxetine 20 mg/5 mL. How
many milligrams of fluoxetine are in
a 10 mL b 25 mL c 40 mL of the solution?
6. A suspension contains erythromycin 250 mg/5
mL. How many milligrams of erythromycin are in
a 10 mL b 20 mL c 30 mL of the suspension?
7. A syrup contains chlorpromazine 25 mg/5 mL.
How many milligrams of chlorpromazine are in
a 10 mL b 30 mL c 50 mL of the syrup?
8. A mixture contains penicillin 250 mg/5 mL. How
many milligrams of penicillin are in
a 15 mL b 25 mL c 35 mL of the mixture?
Dosage Calculations Exercise 3 – Answers
All answers are in mg
1
a)
20
b)
30
c)
50
2
a)
6
b)
10
c)
14
3
a)
800
b)
200
c)
400
4
a)
500
b)
750
c)
1000
5
a)
40
b)
100
c)
160
6
a)
500
b)
1000
c)
1500
7
a)
50
b)
150
c)
250
8
a)
750
b)
1250
c)
1750
44
Dosage Calculations Exercise 4
In each example, you are given the prescribed
dosage and the strength of stock on hand.
Calculate the volume to be given:
1. Ordered: penicillin 500 mg
On hand: syrup 125 mg/5 mL
2. Ordered: furosemide (frusemide) 40 mg
On hand: solution 10 mg/mL
3. Ordered: morphine hydrochloride 100 mg
On hand: solution 40 mg/mL
4. Ordered: paracetamol 180 mg
On hand: suspension 120 mg/5 mL
5. Ordered: phenytoin 150 mg
On hand: suspension 125 mg/5 mL
6. Ordered: erythromycin 1250 mg
On hand: suspension 250 mg/5 mL
7. Ordered: fluoxetine 30 mg
On hand: solution 20 mg/5 mL
8. Ordered: penicillin 1000 mg
On hand: mixture 250 mg/5 mL
9. Ordered: chlorpromazine 35 mg
On hand: syrup 25 mg/5 mL
10. Ordered: penicillin 1200 mg
On hand: mixture 250 mg/5 mL
11. Ordered: erythromycin 800 mg
On hand: mixture 125 mg/5 mL
Dosage Calculations Exercise 4 - Answers
All answers are in mL
1.
20
5.
6
9.
7
2.
4
6.
25
10.
24
3.
2.5
7.
7.5
11.
32
4.
7.5
8.
20
45
Dosage Calculations Exercise 5
Dosages of oral medications
1. A patient is ordered paracetamol 1 g, orally.
Stock on hand is 500 mg tablets. Calculate the
number of tablets required.
2. Ordered: codeine 15 mg, orally. Stock on hand:
codeine tablets, 30 mg. How many tablets should
the patient take?
3. A patient is ordered furosemide (frusemide) 60
mg, orally. In the ward are 40 mg tablets. How
many tablets should be given?
4. How many 30 mg tablets of codeine are needed
for a dose of 0.06 gram?
5. 750 mg of ciprofloxacin is required. On hand are
tablets of strength 500 mg. How many tablets
should be given?
6. A patient is prescribed 150 mg of soluble
aspirin. On hand we have 300 mg tablets. What
number should be given?
7. 450 mg of soluble aspirin is ordered. Stock on
hand is 300 mg tablets. How many tablets should
the patient receive?
8. 25 mg of captopril is prescribed. How many 50
mg tablets should be given?
9. The stock on hand of diazepam is 5 mg tablets.
How many tablets are to be administered if the
order is diazepam 12.5 mg?
10. Digoxin 125 mcg is ordered. Tablets available
are 0.25 mg. How many tablets should be given?
Check that you have used the same unit of
weight throughout a calculation. Are both weights
in milligrams (mg)? Or are both weights in
micrograms (mcg)?
46
Dosage Calculations Exercise 5 - Anwers
All answers are in tablets
1.
2
5.
1
9.
2.
1
6.
or 0.5
10.
or 0.5
3.
1
7.
1
4.
2
8.
or 0.5
47
Dosage Calculation Exercise 6
Calculate the volume of stock required. Give
answers greater than 1 mL correct to one decimal
place; answers less than 1 mL correct to two
decimal places.
Ordered
Stock ampoule
1. Morphine
12 mg
15 mg/mL
2. Calciparine
7000 units
25 000 units in 1 mL
3. Benzylpenicillin
1500 mg
1.2 g in 10 mL
4. Heparin
3000 units
5000 units/mL
5. Phenobarbitone
70 mg
200 mg/mL
6. Pethidine
80 mg
100 mg/2 mL
7. Buscopan
0.24 mg
0.4 mg/2mL
8. Digoxin
200 mcg
500 mcg in 2 mL
9. Furosemide (frusemide)
150 mg
250 mg in 5 mL
10. Ondansetron
5 mg
4 mg in 2 mL
11. Capreomycin
800 mg
1 g in 5 mL
12. Tramadol
120 mg
100 mg in 2 mL
13. Gentamicin
70 mg
80 mg in 2 mL
14. Vancomycin
800 mg
1 g in 5 mL
15. Morphine
7.5 mg
10 mg in 1 mL
16. Ceftriaxone
1250 mg
1 g/3 mL
17. Buscopan
25 mg
20 mg in 1 mL
18. Dexamethasone
3 mg
4 mg/mL
19. Vancomycin
1.2 g
1000 mg/5 mL
20. Naloxone
0.5 mg
0.4 mg/mL
48
Dosage Calculations Exercise 6 – Answers
All answers are in mL
1.
0.8
6.
1.6
11.
4
16.
3.8
2.
0.28
7.
1.2
12.
2.4
17.
1.3
3.
12.5
8.
0.8
13.
1.8
18.
0.75
4.
0.6
9.
3
14.
4
19.
6
5.
0.35
10.
2.5
15.
0.75
20.
1.3
49
Dosage Calculations Exercise 7
Calculate the volume of stock to be drawn up for
injection.
1. Pethidine 60 mg is ordered. Stock ampoules
contain 100 mg in 2 mL.
2. An adult is ordered metoclopramide 15 mg, for
nausea. On hand are ampoules containing 10
mg/mL.
3. A patient is prescribed erythromycin 250 mg,
I.V. Stock on hand contains 1 g in 10 mL, once
diluted.
4. Tramadol hydrochloride 80 mg is required.
Available stock contains 100 mg in 2 mL.
5. A patient is ordered benzylpenicillin 800 mg. On
hand is benzylpenicillin 1.2 g in 6 mL.
6. An adult patient with TB is to be given 500 mg
of capreomycin every second day, I.M.I. Stock on
hand contains 1 g in 3 mL.
7. Digoxin ampoules on hand contain 500 mcg in 2
mL. Digoxin 150 mcg is ordered.
8. Stock Calciparine contains 25 000 units in 1 mL.
15 000 units of Calciparine are ordered.
9. Penicillin 450 mg is ordered. Stock ampoules
contain 600 mg in 5 mL.
Dosage Calculations Exercise 7 - Answers
All answers are in mL
1.
1.2
4.
1.6
7.
0.6
2.
1.5
5.
4
8.
0.6
3.
2.5
6.
1.5
9.
3.75 (3.8 to 1dp)
50
Dosage Calculations Exercise 8
1. An injection of morphine 8 mg is required.
Ampoules on hand contain 10 mg in 1 mL. What
volume is drawn up for injection?
2. Digoxin ampoules on hand contain 500 mcg in 2
mL. What volume is needed to give 350 mcg?
3. A child is ordered 9 mg of gentamicin by I.M.I.
Stock ampoules contain 20 mg in 2 mL. What
volume is needed for the injection?
4. A patient is to be given flucloxacillin 250 mg by
injection. Stock vials contain 1 g in 10 mL, after
dilution. Calculate the required volume.
5. Stock heparin has a strength of 5000 units per
mL. What volume must be drawn up to give 6500
units?
6. Pethidine 85 mg is to be given I.M. Stock
ampoules contain pethidine 100 mg in 2 mL.
Calculate the volume of stock required.
7. A patient is to receive an injection of gentamicin
60 mg, I.M. Ampoules on hand contain 80 mg/2
mL. Calculate the volume required.
8. A patient is prescribed naloxone 0.6 mg, I.V.
Stock ampoules contain 0.4 mg/2 mL. What
volume should be drawn up for injection?
Think about each answer. Does it make sense? Is
it ridiculously large?
Dosage Calculations Exercise 8 - Answers
All answers are in mL
1.
0.8
4.
2.5
7.
1.5
2.
1.4
5.
1.3
8.
3.0
3.
0.9
6.
1.7
51
Suggested Reading
Drug Calculations for Nurses-A Step By Step
Approach
Robert Lapham and Heather Agar
ISBN 0-340-60479-4
Nursing Calculations Fifth Edition
J.D. Gatford and R.E.Anderson
ISBN 0-443-05966-7
Disclaimer
Please note that the author of this document has
no nursing or medical experience. The topics in
this leaflet are dealt with in a mathematical context
rather than a medical one.
We would appreciate your comments on this
worksheet, especially if you’ve found any errors,
so that we can improve it for future use. Please
contact the Maths Skills Adviser by email at
skills@hull.ac.uk
The information in this leaflet can be made
available in an alternative format on request using
the email above.