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LPN INTENSIVE CALCULATIONS�� MODULE TWO�� INTENSIVE GPHC Exam revision � programme

LONDON PHARMACIST NETWORK (LPN)

INTENSIVE REVISION FOR

GPHC EXAM.

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OPENING REMARKS

Book sign means resource questions
USE LAPTOP OR DESKTOP
CALC SESSION 2 of 10
GET CALCULATOR. GET NOTES PAD and PEN
PAID REVISION SESSION so , DO NOT SHARE LINK/ MATERIALS for this session.
MENTAL BREAK 5 – 10 MINS
YOU WILL BE SENT PRACTICE QUESTIONS AFTER SESSION
STAY ACTIVE ATTEMPT QUESTIONS AND ASK QUESTIONS

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TODAY’S TOPICS

DISPLACEMENT VOLUMES🫙 ✅
ALCOHOL UNITS 1 🍻🥂✅
CREATININE CLEARANCE 🚑✅
CONCENTRATIONS🧪 ✅
SIMPLE DILUTION 🫗✅

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QUESTION 1 - DISPLACEMENT VOLUME

You receive a prescription for an antibiotic. For reconstitution, 68mL of water is needed to produce 100mL of an antibiotic containing 250mg of Amoxicillin in every 5ml dose. Calculate the displacement volume for a quantity of powder equivalent to the 250mg dose of Amoxicillin. Answer to 1.d.p

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ANSWER 1 - DISPLACEMENT VOLUME

If there is 250mg in each 5mL dose, 100mL has 20-times this – that is to say, 5,000mg.
If 68mL is needed, it means 5,000mg displaces the remaining 32mL of water.
Thus, 5,000mg displaces 32mL in 100mL; therefore, 250mg displaces 1.6mL in a 5mL dose.
ANSWER = 1.6mL

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QUESTION 2- DISPLACEMENT VOLUME

A patient with a severe infection is prescribed meropenem at 1.25 g every 8 hours via IV infusion over 30 minutes. The available stock is 500 mg vials, which when reconstituted by adding sterile water to each vial. the final concentration after reconstituting a vial is 49mg/ml. You are aware that 500mg meropenem has a displacement volume of 0.1ml. Using the information provided, calculate the volume of sterile water that was added to reconstitute a 500mg meropenem vial.

ANSWER to 1 d.p.

UK’s most INTENSIVE GPhC exam calculations

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ANSWER 2- DISPLACEMENT VOLUME

49mg = 1ml

500mg = 10.204ml

Total volume – DV = volume added

10.204ml – 0.1ml = 10.1ml

ANSWER = 10.1ml

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QUESTION 3 - DISPLACEMENT VOLUME

A 4-year-old child, who weighs 14 kg, has been prescribed intravenous amoxicillin 20 mg/kg every 8 hours. 250mg of amoxicillin has a displacement value of 0.2mL in water for injection. 10 mL of water for injection is added to a 500 mg vial of amoxicillin.
How many mL need to be drawn out of the vial for this dose?
Round your answer to the nearest whole number

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ANSWER 3 - DISPLACEMENT VOLUME

10ml + 0.4ml = 10.4ml
500mg = 10.4ml
14 x 20 = 280mg
if 500 = 10.4ml , 280 = x
x = 5.824ml
ANSWER = 6ml

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QUESTION 4 - DISPLACEMENT VOLUME

A 5-year-old child, who weighs 34.2 kg, has had IM Cefuroxime at 50 mg/kg every 8 hours as recommended by microbiology for a susceptible infection. The required number of 750 mg vials have been reconstituted with 3 mL of water for injection each, ready for IM administration. See resource provided.
How many ml of the reconstituted cefuroxime will be required for each dose? Give your answer to nearest whole number.

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ANSWER 4 - DISPLACEMENT VOLUME

34.2 x 50 = 1710mg

IM injection , final concentration is 216mg/ml
216 = 1 ml
1710 = 7.9166ml

X = 8 ml

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QUESTION 5 - DISPLACEMENT VOLUME

Adam a-5- year-boy is prescribed 100ml bottle of PEN.V. 125mg/5ml at a dose of 5ml QDS. To reconstitute , the dispenser is supposed to add 82ml of water to the powder and shake the mixture vigorously. Unfortunately, the dispenser added 60ml of water instead by mistake.
How much drug will each dose contain in the volume he takes due to the dispenser’s error?
Round ANSWER in mg to nearest whole number

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ANSWER 5 - DISPLACEMENT VOLUME

125mg in 5ml
in a 100ml bottle of penicillin v , we will have 2500mg
USUALLY, the displacement vol = 18ml
DUE TO THE ERROR , total volume will be 60ml plus 18ml = 78ml
SO, if 2500mg = 78ml
Then x = 5ml (dose)
X = 160mg answer

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ALCOHOL UNITS QUESTION 1

Calculate units of alcohol consumed

UNITS of alcohol = (vol of drink (ml) x ABV%)

1000

Assume medium glass of wine is 175ml, small glass is 125ml and 1 pint is 568ml

Calculate alcohol units intake over a period of 14 days for a woman who drinks 2 small glasses of wine 12% every other day.

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ANSWER 1 – ALCOHOL UNITS

125 x 2 x 7 x 12 = 21

1000

ANSWER = 21 UNITS

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ALCOHOL UNITS QUESTION 2

Calculate units of alcohol consumed

UNITS of alcohol = (vol of drink (ml) x ABV%)

1000

Assume medium glass of wine is 175ml, small glass is 125ml and 1 pint is 568ml

Calculate alcohol units over the recommended weekly limit for a woman who drinks 2 small glasses of wine 12% every day and 2 pints of beer (5%) on a Saturday night every week.
Give your answer as a whole number

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ANSWER 2 – ALCOHOL UNITS

2 x 125 x 12 x 7 = 21
1000

2 x 568 x 5 = 5.68
1000
26.68 - 14 = 12.68 UNITS
= 12.68 UNITS
Answer =13 units

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ALCOHOL UNITS QUESTION 3

You are conducting a health check with a 35 -year-old woman. You decide to discuss her weekly alcohol intake. She informs you that, on average, in a week she enjoys a glass of red wine (13% ABV) with her evening meal per day and on Saturday nights she drinks 2 cocktails (10%) .

Units of alcohol = volume of drink (ml) x ABV (%)

1000

Where ABV is alcohol by volume

Given that each glass of wine is 175ml, a cocktail is 200ml , a shot of whiskey is 25ml and 1 pint is 568ml, by how many units of alcohol should this patient reduce her intake in order to be at the recommended weekly limit? Give your answer as whole number.

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ANSWER 3 – ALCOHOL UNITS

Units of wine = 1225(ml) x 13 (%) = 15.925

1000

Units from cocktail = 400(ml) x 10 (%) = 4

1000

15.925 + 4 = 19.925 = 19.925
19.925 – 14 = 5.925

ANSWER = 6 units

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ALCOHOL UNITS QUESTION 4

You are conducting a health check with Amy, a 45 -year-old woman. You advise her on healthy eating and exercise and, as part of this are discussing her weekly alcohol intake. She informs you that, on average, in a week she enjoys a glass of red wine (13% ABV) with her dinner daily , then on Fridays, she also drinks 3 pints of larger (4% ABV) after work and on Saturday nights she drinks 2 glasses of pina-colada cocktail (10%) which is her favourite cocktail in a local bar.

Units of alcohol = volume of drink (ml) x ABV (%)

1000

Where ABV is alcohol by volume

Given that each glass of wine is 175ml, a glass of cocktail is 100ml and 1 pint is 568ml, by how many units of alcohol should this patient reduce her intake in order to be at the recommended weekly limit? Give your answer to as whole number.

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ANSWER 4 – ALCOHOL UNITS

Units of wine = 1225(ml) x 13 (%) = 15.925
1000
Units of alcohol = 1704(ml) x 4 (%) = 6.816

1000

Units of alcohol = 200 x 10 = 2
1000
15.925 + 6.816 = 22.741 plus 2 = 24.741
24.741 – 14 = 10.741

Units of alcohol FORMULA = volume of drink (ml) x ABV (%)
1000
ANSWER = 11 units

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CREATININE CLEARANCE - 1

What is the recommended total daily dose of meropenem in mg/Kg for this man? 1D.P.
See link below
Meronem IV 500mg - Summary of Product Characteristics (SmPC) - (emc) (medicines.org.uk)

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ANSWER 1 – CREATININE CLEARANCE

(140 – Age) × Weight × Constant

Serum creatinine

Crcl = 26.54ml/min
For renal impairment = dose is 2g every 12 hours
so 4g per day
4000/67 = 59.70mg

Answer = 59.7mg/kg

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QUESTION 2

You are assessing the kidney function of a male transgender patient, who has been admitted to the renal ward of your hospital. The patient has not undergone any hormonal, medical or surgical changes. Given that the patient is 80-years-old and has a weight of 66kg and is 165cm tall with a serum creatinine is 280 micromol/L. Calculate the recommended total daily dose of meropenem in mg/Kg for management of febrile neutropenia. Answer to 2.dp. Use link below

Male constant = 1.23 female = 1.04

Meronem IV 500mg - Summary of Product Characteristics (SmPC) - (emc) (medicines.org.uk)

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QUESTION 2 ANSWER

CRCL = 14.70 ml/min

From resource, give half of recommended dose.

50% of 1g = 500mg twice a day daily

1000/ 66 =

15.15mg/kg answer

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QUESTION 3

Alfonso a-75-year-old male who weighs 70kg has been admitted with partial seizures. The doctor on the ward has decided to initiate the patient on levetiracetam and asks for your recommendation for an appropriate dose. You notice the patient’s serum creatinine is 300 micromol/litre and suspect that the patient’s renal function may be impaired. You decide to calculate the patient’s creatinine clearance using the formula provided below. A link/resource for the drug is also provided underneath. Constant =1.23

Levetiracetam 500 mg film-coated tablets - Summary of Product Characteristics (SmPC) - (emc) (medicines.org.uk)

Calculate the maximum daily dose of levetiracetam in mg/kg the patient should receive taking into consideration the patient’s CrCl. Answer to 1.d.p.

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ANSWER 3

18.655ml/min

CrCl approximately = 20 ml/minute

If eGFR < 30ml/minute/1.73m2 = 250mg to 500mg twice a day

maximum daily dose should be 1g daily

1000mg/70kg

= 14.2857mg/kg

ANSWER = 14.3mg/Kg

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CREATININE CLEARANCE - 4

Esther is 80 years old and has an ideal body weight of 66 kg. She has been prescribed cefalexin. Cefalexin is principally excreted renally. The dose recommendations for the drug are as noted below. Esther has a serum creatinine of 280 micromol/L

CrCL (mL/min) -- Dosage (140 – Age) × Weight × Constant

Serum creatinine

>70 -- 350 mg twice daily
50-69 - 175 mg twice daily
25-49 -- 175 mg daily
10-24 -- 87.5 mg daily
<10 -- 87.5 mg three times weekly
Constant is 1.04 for women and 1.23 for men
Given that cefalexin is available as 250mg/5ml oral suspension and Esther will be using a syringe calibrated at 0.1ml intervals, how much volume will you supply for a week’s course?
Answer to 1.d.p.

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ANSWER 4 – CREATININE CLEARANCE

creatinine clearance = 14.70 ml/min
87.5mg daily
1.75ml daily, approximately 1.8ml
1.8ml x 7 since using 0.1ml syringe intervals
ANSWER = 12.6ml

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CONCENTRATION

TYPES

%W/V , %v/v
PPM
1g in 1000 / 100 etc.

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CONCENTRATION

1. Convert 1 in 2000 to %w/v
2. Convert 1 in 10000 to %w/v
3. Convert 25%w/v to g in 1000
4. Convert 0.1%w/v to PPM

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QUESTION 1- concentration

Express the concentration of this cream in %w/w.
ANSWER TO 1.d.p

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ANSWER 1 - CONCENTRATION

concentration of the cream is written as 1mg/g
Change to percentage means x in 100g
If 1mg = 1g
100mg = 100g
100mg = 0.1g
Hence 0.1% W/W
ANSWER = 0.1% w/w

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QUESTION 2 - CONCENTRATION

You are working as a pharmacist and are required to dispense a solution of chlorhexidine by making 1 in 40 dilution of your stock. You have a 200ml bottle of chlorhexidine 0.5% in stock.
What is the concentration of the solution you need to dispense in parts per million ?

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ANSWER 2

stock solution = 0.5% i.e. 0.5 = 100
0.5/40 = 0.0125
0.0125 %
0.0125 = 100
x = 1000000

X = 125 PPM

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Concentration 3

You have 500ml of 2%w/v normal saline in stock.
5ml of the solution was measured out and diluted to 20ml with water.
What is the concentration of the final solution in %w/v?
Answer to 1.dp

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Answer 3

5ml to 20ml D/F = 4
2% ÷ 4 = 0.5%
ANSWER = 0.5%W/V

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Concentration 4-

You have 0.2%w/v of normal saline in stock. 10ml of the solution was measured out and diluted to 60ml with water. What is the concentration of the final solution in %w/v?
Answer to 2.dp

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Answer 4- CONCENTRATION

0.2 = 100ml
0.2g = 10ml
Dilution factor is 6 from 10ml to 60ml
0.2/6 = 0.03
ANSWER = 0.03%W/V

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Question 1- SIMPLE DILUTION

You work for a pharmaceutical company. How much of a stock 7.5%w/v solution of potassium permanganate do you require to make 3500ml of a 5%w/v solution?

Answer to nearest ten.

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ANSWER 1

C1V1 = C2V2
7.5 X V1 = 5 X 3500
V1 = 5 X 3500

7.5

V1 = 2333.333ml

ANSWER = 2330 ml

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QUESTION 2 -SIMPLE DILUTION

A patient is required to use 20ml of chlorhexidine 0.03%w/v mouthwash twice a day for 10 days. You have a stock of 1000ml bottle of chlorhexidine 5%w/v.
Calculate the volume of your stock required to ensure the patient completes the entire treatment.
Round your answer to nearest 0.5ml

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Answer 2 - SIMPLE DILUTION

C1V1 = C2V2
NOTE V2 = 20ml x 2 = 40ml x 10 days = 400ml
5 X V1 = 0.03 X 400ML
V1 = 2.4 ml

ANSWER = 2.5ml

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QUESTION 3- SIMPLE DILUTION

A doctor asks you to prepare 300g of a 1 in 6 dilution of hydrocortisone 1%w/v cream. The recommended diluent is white soft paraffin. Calculate how many grams of hydrocortisone 1%w/v cream is needed to prepare the requested cream.
Answer as a whole number.

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Answer 3 - SIMPLE DILUTION

Dilution factor 1 in 6 = 6
Meaning there are six parts
300g / 6 = 50g
1 part is 50g
So, weight of hydrocortisone in the cream is 50g

ANSWER = 50g

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Question 4- SIMPLE DILUTION

You have 100 mL of a 1 in 40 glucose solution in stock. The entire stock volume is diluted to 2000 ml using water .

Find the exact concentration of the diluted product as a percentage strength %w/v .

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ANSWER 4

1 in 40 . Hence 2.5 in 100. so, 2.5%w/v
From 100ml to 2000ml . Dilution Factor is 20

So, 2.5% w/v / 10 = 0.125

0.125%w/v

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QUESTION 5 - dilution

You have 0.2%w/v of potassium citrate in stock. 5ml of the potassium citrate solution was measured out and diluted to 50ml with water. This resulting solution was then also diluted 1 in 10 further . What is the concentration of the final solution in PPM ?

Answer as whole number

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Simple dilutions - Answer 5

0.2g = 100 ml
0.2 = 5 ml
Diluted to 50ml means dilution factor is 10
0.2/10 = 0.02

Further 1 in 10 means 0.02/10 again

FINAL CONC = 0.002%w/v
ANSWER = 20 PPM

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