LPN INTENSIVE CALCULATIONS�� TUTORIAL TWO��� INTENSIVE GPHC Exam revision � programme FOR NOV 2025

LONDON PHARMACIST NETWORK (LPN)

INTENSIVE REVISION FOR NOV 2025

GPHC EXAM.

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OPENING REMARKS

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• 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

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• DISPLACEMENT VOLUMES ✅
• ALCOHOL UNITS 1 ✅
• CREATININE CLEARANCE ✅
• CONCENTRATIONS ✅
• SIMPLE DILUTION ✅

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QUESTION 1 - DISPLACEMENT VOLUME

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• 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

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• 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

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• 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 2 - DISPLACEMENT VOLUME

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• 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 3 - DISPLACEMENT VOLUME

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• A 5-year-old child, who weighs 24.2 kg, has had IV 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 diluted with 6 mL of water for injection each, ready for IV bolus administration.
• 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 3 - DISPLACEMENT VOLUME

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• 24.2 x 50 = 1210mg

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• Iv bolus , final concentration is 116mg/ml
• 116 = 1 ml
• 1210 = x

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• X = 10 ml

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QUESTION 4 - DISPLACEMENT VOLUME

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You work as a hospital pharmacist.

You are required to reconstitute an antibiotic vial.

The label for a 15g vial says “add 20ml of water for injection to create a solution with a concentration of 60%w/v.

Unfortunately, the dispenser added 30ml of water for injection instead of 20ml.

What concentration in g/ml would be obtained if 30ml of diluent was added to the vial instead of 20ml?

Give your answer to the nearest 0.05.

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ANSWER 4 - DISPLACEMENT VOLUME

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TOTAL VOLUME = vol added + displacement volume

• find total volume from final concentration 60%w/v
• If 60g = 100ml
• 15g = 25ml
• 25ml = 20ml + DV
• DV = 5ml .
• If 30ml is added by mistake total volume will be 35ml . (vol added + displacement volume)
• Hence 15g = 35ml
• Then 0.428g = 1 ml
• ANSWER = 0.45g/ml

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QUESTION 5 - DISPLACEMENT VOLUME

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• 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

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• 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

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• Calculate units of alcohol consumed

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

1000

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

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• 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

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• 125 x 2 x 7 x 12 = 21

1000

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• ANSWER = 21 UNITS

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ALCOHOL UNITS QUESTION 2

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• Calculate units of alcohol consumed

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

1000

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

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• 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

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• 2 x 125 x 12 x 7 = 21
• 1000

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• 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

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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 , on lady’s night (every Wednesday) she drinks 2 shots of whiskey (40% ABV) 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

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

1000

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

1000

• Units from whiskey = 50 x 40 = 2

1000

• 15.925 + 4 = 19.925 plus 2 = 21.925
• 21.925 – 14 = 7.925

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• ANSWER = 8 units

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ALCOHOL UNITS QUESTION 4

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• A patient would like to discuss his alcohol consumption with you.
• The patient explains that, in a usual week, he drinks about …..
• - 5 cans of medium beer
• - 4 large glasses of wine
• - 8 small bottles of alcopops
• Using the information provided via the link below, calculate how many units of alcohol the patient is consuming per week?
• Give your answer to 1.d.p. Click link below. Use control + click
• (1) alcohol sizes and conent - Bing images

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ANSWER 4 – ALCOHOL UNITS

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• 15 cans of medium beer - 5 x 440 = 2200ml x 4.5% /1000 = 9.9 units
• - 4 large glasses of wine - 4 x 250 ml = 1000ml x 12% /1000 = 12 units
• - 8 small bottles of alcopops - 8 x 275 mL = 2,200 mL X 4 % /1000 = 8.8 units

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• 9.9 plus 12 units plus 8.8 units = 30.7 units

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ALCOHOL UNITS QUESTION 5

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 5 – ALCOHOL UNITS

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• 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

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

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CREATININE CLEARANCE - 1

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• CALCULATE CREATININE CLEARANCE FOR A FEMALE PATIENT.
• She is 70 years , weighs 67 kg and has a BMI of 24 kg/m2
• She has a serum creatinine of 267 micromol/litre.
• (140 – Age) × Weight × Constant

Serum creatinine

• • Age in years
• •Weight in kilograms (use ideal bodyweight where fat is likely to be the major contributor to body mass)
• • Serum creatinine in micromol/litre
• • Constant = 1.23 for men; 1.04 for women
• ANSWER TO NEAREST 0.5ml/min

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ANSWER 1 – CREATININE CLEARANCE

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• (140 – Age) × Weight × Constant

Serum creatinine

• (140 – 70) × 67 × 1.04 = 18.268 ml/ min

267

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• 18.5ml/min ANSWER

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CREATININE CLEARANCE - 2

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• 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 2 – CREATININE CLEARANCE

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• (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

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• Answer = 59.7mg/kg

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CREATININE CLEARANCE - 3

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• Patient X a-63-year-old Transgender man weighs 67 kg and is to be treated with clarithromycin via iv infusion. Patient X has a serum creatinine of 267 micromol/L . Patient X has not undergone any hormonal, medical or surgical changes.

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• FORMULA = (140 – Age) × Weight × Constant

Serum creatinine

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• • Constant = 1.23 for men; 1.04 for women
• What is the maximum recommended daily dose for this patient in mg/kg?

Using Cockcroft Gault equation provided

• ANSWER TO 2.D.P

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• Clarithromycin 500mg powder for solution for infusion vials - Summary of Product Characteristics (SmPC) - (emc) (medicines.org.uk)

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ANSWER 3 – CREATININE CLEARANCE

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• Cockcroft Gault FORMULA = (140 – Age) × Weight × Constant

Serum creatinine

• formula = 77 x 67 x 1.04

267

• 20.09 ml/ min
• From SPC 500mg as cr/cl is less than 30ml/min
• Daily DOSE = 500MG
• 500MG / 67kg = 7.46mg/kg

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CREATININE CLEARANCE - 4

Esther is 64 years old and has an ideal body weight of 65 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 200 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

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• creatinine clearance = 25.688
• 175mg daily
• 3.5ml daily
• 3.5ml x 7 since using 0.1ml syringe intervals
• ANSWER = 24.5ml

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CONCENTRATION

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TYPES

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

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CONCENTRATION

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• 1. Convert 1 in 5000 to %w/v
• 2. Convert 1 in 10000 to %w/v
• 3. Convert 25%w/v to g in 1000
• 4. A cream contains 12 g of hydrocortisone made up to 200 g with cream base. What is the percentage concentration?
• 5. Convert 0.1%w/v to PPM

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CONCENTRATION 1

• A pharmacist has a 9% w/v sodium chloride concentrate in stock. He receives instructions to produce 50ml of a new solution by making a 1 in 8 dilution of the stock solution using distilled water.
• Calculate the concentration in %w/v of the new solution once he makes the required dilution.
• Give your answer as 1 d.p.

CONCENTRATION - ANSWER 1

• Initial stock concentration = 9% w/v
• 1 in 8 dilution = 9/8 = 1.125
• Answer to 1.d.p = 1.1%w/v

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 ?

ANSWER 2

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

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• X = 125 PPM

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

Question 1- SIMPLE DILUTION

You work for a pharmaceutical company. How much of a stock 8.5%w/v solution of potassium permanganate do you require to make 450ml of a 5%w/v solution?

Answer to nearest ten.

ANSWER 1

• C1V1 = C2V2
• 8.5 X V1 = 5 X 450
• V1 = 5 X 450

8.5

V1 = 264.705

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ANSWER = 260 ml

Question 2 - DILUTION

Ms. P is prescribed 1 in 5000 solution of potassium chloride and needs 500ml TDS for 1 week. The hospital has 500ml of 2%w/v potassium chloride in stock.

How much volume in ml of the stock solution will be required to supply for Ms. P’s entire treatment? Answer as whole number

ANSWER 2

• STOCK VS NEW SOLUTION
• C1v1 = c2v2
• 2 x v1 = 0.02 x 10500
• v1 = 0.02 x 10500

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• V1 = 105 ml

Question 3- SIMPLE DILUTION

You work in a hospital where a patient requires an infusion of glucose solution.

You are required to calculate how much water you would add to a 5%w/v solution of glucose to make 400ml of a 2%w/v solution?

Answer to nearest whole number.

• LONDON PHARMACIST NETWORK

ANSWER 3

• C1V1 = C2V2
• 5 X V1 = 2 X 400
• V1 = 2 X 400

5

V1 = 160ml

400 – 160ml = 240

ANSWER = 240 ml

Question 4- SIMPLE DILUTION

You have 100 mL of a 1 in 50 glucose solution in stock. The entire stock volume is diluted to 1000 ml using water .

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

ANSWER 4

• 1 in 50 . Hence 2 in 100. so, 2%w/v
• From 100ml to 1000ml . Dilution Factor is 10

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• So, 2% w/v / 10 = 0.2

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• 0.2%w/v

Question 5- SIMPLE DILUTION

You have 5%w/v chloride solution in stock.

How much of your stock do you need to make 300ml of a 2%w/v solution?

ANSWER 5

• C1V1 = C2V2
• 5 X V1 = 2 X 300
• V1 = 600 / 5 = 120ml

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• ANSWER = 120ml

THE END

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