LPN INTENSIVE CALCULATIONS�� CALCULATIONS WORKBOOK 4 ��� INTENSIVE GPHC Exam revision � programme FOR JUNE 2025

LONDON PHARMACIST NETWORK (LPN)

INTENSIVE REVISION FOR JUNE 2025

GPHC EXAM.

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TODAY’S TOPICS

• RDA OF SODIUM ✅
• ROTIGOTINE PATCHES ✅
• CLINICAL TRIALS✅
• HALF LIFE ✅
• INCREASE IN OPIOID DOSES ✅

RDA -QUESTION 1

• A 10-year-old patient has been prescribed phenytoin 20mg/5ml solution at a dose of 0.4mg/kg twice daily . Every 5ml of Phenytoin solution contains 2.2mmol of sodium. The child weighs 70 lbs . Given that the RDA of NaCl for a child is 3g (1.2g sodium) . Calculate the % RDA of sodium in her daily sodium intake from phenytoin .units =1 lb = 0.45kg
• Na = 23, Cl = 35.5 , NaCl = 58.5
• ANSWER TO 1 D.P

RDA OF PROTEIN - 2

• Mr. Kim weighing 120 pounds has been prescribed 0.45g per kg twice a day of protein by his nutritionist to manage malnutrition for 4 weeks. He has been supplied ensure drinks to support his nutritional intake. Given that the recommended daily allowance of protein for a woman is 45g per day and for a man is 56g/day.
• Calculate the % recommended daily allowance of protein in his daily intake from ensure drinks. ANSWER TO 2.D.P.
• 1 Lb = 0.45kg

RDA - QUESTION 3

• Amy a 22-year-old patient is taking sodium citrate oral sachets to relieve symptoms of cystitis. She takes the content of one sachet mixed in 200ml of water every 6 hours. Cystitis sachets also contains NaCl and provides a total of 2mmol of Na+ per sachet. The recommended daily allowance (RDA ) of salt for an infant is 1g (0.4g of sodium) and for an adult is 6g (2.4g of sodium).
• The atomic mass of sodium is 23.

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• What percentage of Amy’s recommended daily salt allowance is contained in her daily dose of cystitis relief sachets?
• ANSWER TO 1 .D.P
• Watch London Pharmacist Network videos on YouTube

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RDA - QUESTION 4

• Angel a-6-month-old baby has been prescribed Gaviscon sachets at a dose of one sachet with feeds every four hours. Her mother has been asked to continue treatment for a month then review. Gaviscon sachet contain 0.92 mmol of Na +.
• RDA of salt for Angel is 1g (equivalent to 0.4g sodium) per day.
• What percentage of Angel’s recommended daily sodium allowance is contained in her daily dose of Gaviscon sachets?
• ANSWER TO 1.D.P

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QUESTION 5 - RDA OF PROTEIN

• A transgender man weighing 160 pounds has been prescribed 0.25g per kg twice a day of protein by the nutritionist to manage malnutrition for 6 weeks. The patient has been supplied fresubin high protein to support nutritional intake. The patient has not undergone any surgical or hormonal changes. Given that the recommended daily allowance of protein for a woman is 45g per day and for a man is 56g/day.
• Calculate the % recommended daily allowance of protein in the daily intake from fresubin high protein. ANSWER as whole number.
• 1 Lb = 0.45kg

QUESTION 6 – R.D.A

Miss . G a 3-year-old has been prescribed Gaviscon Infant Sachets one dose with feeds, 6 times in 24 hours. Assume Gaviscon Infant sachets contain 0.95mmol Na+/dose. The recommended daily allowance (RDA) of salt for this patient is 3g (equivalent to 1.2 g sodium) per day. The atomic mass of sodium is 23.

What percentage of this child’s recommended daily salt allowance is contained in a total daily dose of Gaviscon Infant Sachets? ANSWER AS WHOLE NUMBER

Give your answer to the nearest whole number.

Watch London pharmacist Network on YouTube

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ANSWER 1 RDA

• 0.4mg per kg
• 0.4mg x 31.5kg = 12.6mg
• 12.6mg x 2 = 25.2mg per DAY
• 20mg = 5ml
• 25.2 = 6.3 ml
• 5ml = 2.2 mmol then 6.3ml = 2.772 mmol
• 2.772 mmol x 23 = 63.756mg i.e 0.063756g
• 0.06376/1.2 x 100 = 5.31%
• ANSWER = 5.3%

ANSWER 2 RDA

• 120 lbs = 54kg
• 0.45g x 54 = 24.3g per dose
• 24.3 x 2 = 48.6g per day

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• 48.6/56 x 100 = 86.7857

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• ANSWER = 86.79%

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ANSWER- RDA 3

• FOUR SACHETS per day = 2mmol x 4 = 8 mmol
• Using mole = mass / mr
• 8mmol = mass (mg)/ 23 mmol/mg
• Mass = 184mg or 0.184g

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• Then if 2.4g of Na+ = 6 g of salt
• 0. 184g Na+ = 0.46 g of salt

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• HENCE 0.46g/6g x 100 = 7.666
• ANSWER = 7.7%

ANSWER- RDA 4

• Gaviscon Infant Sachets contains 0.92mmol Na+/dose.
• 0.92 x 23 = 21.16mg per dose
• 6 doses a day = 6 x 21.16 = 126.96
• SO, 126.96 x 100/400= 31.74%
• ANSWER = 31.7%

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ANSWER RDA 5

• 160 lbs = 72kg
• 0.25g x 72 = 18g per dose
• 18 x 2 = 36g per day

The patient has not undergone any surgical or hormonal changes. So , biologically still a woman.

• 36/45 x 100 = 80

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• ANSWER = 80%

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ANSWER 6 - RDA

• 0.95 X 6 = 5.7 MMOL
• MOLE = mass/ Mr
• 5.7 mmol = mass / 23
• Mass = 131.1mg or 0.1311g OF SODIUM
• We know that 1.2g = 3g of salt
• Hence 0.1311g = 0.32775 OF salt
• 0.32775/ 3 = 0.10925
• 0.10925 x 100 = 10.925
• ANSWER = 11%

QUESTION 1

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Mrs. E. is a 71-year-old Parkinson’s disease patient who needs to be switched to rotigotine patches. She currently takes

• Sinemet, one tablet QDS
• Entacapone 100mg tablets 1 Daily
• Ropinirole 7mg every day.

Calculate what strength of rotigotine patches, Miss E should be prescribed every 24 hours.

Use resource provided above.

• LONDON PHARMACIST NETWORK INTENSIVE CALCULATIONS

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�QUESTION 2

MRS .G. is a 62-year-old Parkinson’s disease patient who needs to be switched to rotigotine patches. She currently takes

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• Co-careldopa MR 125 capsules 1 TDS
• Entacapone 200mg tablets – 1 TDS
• bromocriptine 10 mg tablets every evening.

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Calculate what strength of rotigotine patches, should be prescribed every 24 hours. Ans to nearest whole number

�QUESTION 3

• Mr Sugar is a 60-year-old Parkinson’s disease patient who needs to be switched to rotigotine patches. He currently takes
• STALEVO 100mg/25mg/200 mg 2 tablets TDS
• Cabergoline 2mg tablets every evening.
• Calculate what strength of rotigotine patches, he should be prescribed every 24 hours. Use the resource provided above.
• Each STALEVO tablet contains 100 mg of levodopa, 25 mg of carbidopa and 200 mg of entacapone.

QUESTION 4

• Mr Adu takes the following medication for Parkinson’s Disease:
• - co-careldopa MR 25/100 mg tablets, 1 tds
• - bromocriptine 10 mg tablets, 1 per day
• - opicapone 50 mg tablets, 1 ON
• The nurse on duty asks for your advice in converting him to a rotigotine patch as he can no longer swallow tablets .
• Using the information provided in the resource , calculate the total strength of rotigotine patches, in mg, required for Mr. Adu per day

�QUESTION 5

• Miss P is a 60-year-old Parkinson’s disease patient who needs to be switched to rotigotine patches. She currently takes
• Co-beneldopa 25/250 MR capsules 1 TDS
• Entacapone 100mg tablets – 1 TDS
• Memantine 10mg – 1 ON
• Calculate what strength of rotigotine patches, Miss P should be prescribed every 24 hours

�QUESTION 6

MR K is a 60-year-old Parkinson’s disease patient who needs to be switched to rotigotine patches. he currently takes

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• Co-careldopa MR 125 capsules 1 qds
• Entacapone 200mg tablets – 1 TDS
• bromocriptine 10 mg tablets every evening.

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Calculate what strength of rotigotine patches, MR. K should be prescribed every 24 hours. Ans to nearest whole number

QUESTION 1 ANSWER

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Step 1 - 50 x 4 = 200mg

Step 2 - 200mg x 1.3 = 260mg

Step 3 – 7mg x 20 = 140

Step 4 - 260 + 140 = 400

Step 5 - 400 x 0.55 = 220 mg

220/20 = 11mg

ANSWER =Supply 12mg ropinirole patches

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ANSWER 2

• first step - 100 x 3 = 300mg
• Step 2 – 300 mg x 0.91 = 273
• Step 3 – 10 x10 = 100mg
• 273 + 100 = 373
• Step 4 373 x 0.55 = 205.15 mg
• 205.15 /20 = 10.2575
• ANSWER = 10mg patches to nearest 2mg

ANSWER 3

• first step - 200 x 3 = 600mg
• Step 2 - 600mg x 1.3 = 780
• Step 3 - 2 x100 = 200mg
• 780 + 200 = 980
• Step 4 - 980 x 0.55 = 539 mg
• 539/20 = 26.95
• ANSWER = 16mg patches MAXIMUM

ANSWER 4

• first step - 100 x 3 = 300mg
• Step 2 – 300 mg x 0.91 = 273mg
• Step 3 – 10 x10 = 100mg
• 273+ 100 = 373mg
• Step 4 373 x 0.55 = 205.15 mg
• 205.2/20 = 10.26
• ANSWER = 10mg patches to nearest 2mg

ANSWER 5

• first step - 250 x 3 = 750mg
• Step 2 - 750mg x 0.91 = 682.5
• He takes no dopamine agonist so = 0
• Step 3, 682.5 x 0.55 = 375.375 mg
• Step 4 , 375.375/20 = 18.77mg
• ANSWER = 16mg patches MAXIMUM

ANSWER 6

• first step - 100 x 4 = 400mg
• Step 2 – 400 mg x 0.91 = 364
• Step 3 – 10 x10 = 100mg
• 364+ 100 = 464
• Step 4 464 x 0.55 = 255.2 mg
• 255.2/20 = 12.76
• ANSWER = 12mg ropinirole patches to nearest 2mg

QUESTION 1 – CLINICAL RATIO

• . A company has developed a new drug and are in the process of conducting a phase 3 trial. The trial will include 3 –arm randomized controlled study with an allocation ratio of 1:2:2.

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• What is the total number of patients required to participate in the study so that there are at least 50 patients in each arm?

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QUESTION 2 – CLINICAL RATIO

• . A company has developed a new drug and are in the process of conducting a phase 3 trial. The trial will include 3 –arm randomized controlled study with an allocation ratio of 1:6:6.

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• What is the total number of patients required to participate in the study so that there are at least 100 patients in each arm?

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QUESTION 3- CLINICAL RATIO

• . A company has developed a new drug and are in the process of conducting a phase 3 trial. The trial will include 3 –arm randomized controlled study with an allocation ratio of 1:3:3.

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• What is the total number of patients required to participate in the study so that there are at least 20 patients in each arm?

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ANSWER 1

• 5 x 50 = 250
• Answer = 250

ANSWER 2

• 13 x 100 = 1300
• Answer = 1300

ANSWER 3

PAIN DOSES CALC -QUESTION 1

Mr. Fred is a 45-year-old patient admitted in the orthopedic ward after a car accident. He is to receive 120mg of oxycodone per day via a 10cm syringe driver for pain. The oxycodone dose has been made up to 75ml with water for injection and the syringe driver has been set at a rate of 4.2 mm/hour. Mr. Fred weighs 70kg . What dose of oxycodone in mcg/kg/min is Mr. . Fred going to receive?

ANSWER TO 1 D.P

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OPIOID QUESTION 2

• A 49-year-old man has chronic back pain which has worsened over the last six months. His consultant has decided to stop his codeine tablets and prescribe Oramorph (morphine sulfate) 10 mg/5 mL oral solution to manage the pain. The patient has been taking six codeine 30 mg tablets every day. The consultant decides to use his current codeine dose to prescribe an equivalent amount of morphine sulfate using Oramorph 10 mg/5 mL oral solution every six hours when required. How many milligrams of morphine sulphate will the patient require for 5 days ? Give your answer as a whole number .
• Prescribing in palliative care | Medicines guidance | BNF | NICE

INCREASE IN OPIOID DOSES - QUESTION 3

• An elderly patient takes metoclopramide 10mg , paracetamol 500mg PRN and MST 100mg continuous every day. She also takes 8ml of oramorph oral solution 10mg/5ml QDS for breakthrough pain. What is the maximum dose of morphine she can have per day if her GP decides to increase her dose ?
• ANSWER TO NEAREST TEN.

PAIN DOSES - QUESTION 4

• Mr. D. a 70-year-old male patient takes TRAMADOL 100MG TDS , metformin 500mg BD , zomorph 60mg in the morning and one sevredol 10mg QDS. She also takes 8ml of oramorph oral solution 10mg/5ml QDS for breakthrough pain. What is the minimum dose of morphine she can have per day if her GP decides to increase her dose ? Answer in mg to 2.d.p. Link below
• Prescribing in palliative care | Medicines guidance | BNF | NICE

OPIOID DOSES 5

A 56-year-old lady is going to be converted from oxycodone to tapentadol to achieve better pain management. She currently takes oxycodone modified release 20mg, one twice a day. In addition she takes 5mg capsules for breakthrough pain. She averages at four oxycodone 5mg capsules a day for breakthrough pain.

•  Drug and dose Equivalent oral morphine dose
• Oxycodone 10mg ---- 20mg
• Tapentadol 10mg ---- 4mg

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 What is the equivalent total daily dose of Tapentadol in milligrams? WHOLE NUMBER.

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ANSWER 1

• 120mg = 10cm = 100mm
• If 4.2 mm = 1 hour
• 5.04 mg = 4.2 mm = 1 hour (60 mins)
• x = 1 min
• X = 0.084mg or 84 mcg
• 84mcg per 70 kg
• 1.2mcg = 1kg

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ANSWER 2

• Using the table provided in the resource pack identify how many mg of codeine is
• equivalent to oral (PO) morphine.
• 100mg of codeine = 10mg of PO morphine
• The patient is taking 6 x 30mg of codeine tablets/day= 180 mg of codeine per day.
• 180 mg/10 = 18 mg of PO morphine per day
• 18 x 5 = 90mg
• ANSWER = 90mg

ANSWER 3

100 + 64 = 164MG 

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• 50% of 164 = 82

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• 164 + 82 = 246 mg per day

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• ANSWER = 250 mg

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ANSWER 4

30mg plus 60mg plus 40mg plus 64mg = 194MG 

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• 1/ 3 of 194 = 64.6667

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• 194 + 64.6667 = 258.67 mg per day

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ANSWER 5

• Drug and dose Equivalent oral morphine dose
• Oxycodone 10mg ---- 20mg
• Tapentadol 10mg ---- 4mg

• Total daily dose of oxycodone = 60mg
• 60mg oxycodone = 120mg morphine
• IF 4mg = 10mg Tapentadol
• Then 120mg = x
• 1200/4 = 300

ANSWER = 300mg tapentadol daily

QUESTION – HALF LIFE 1

• Mr. Y. has been prescribed doxycycline at a dose of 100mg once daily. He takes his dose daily at 9am. Calculate how many half-lives it would take to get to 6.25% of the administered dose?
• Answer as a whole number.

HALF-LIFE 2

Drug P contains 400g of paracetamol effervescent which has a half-life of 6 hours. Calculate how long in hours it will take for nearly all of the effervescent paracetamol to evaporate i.e. approx. 0.01 to remain?

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QUESTION – HALF LIFE 3

• Ms. E. has been prescribed sertraline at a dose of 200mg daily. She takes her dose daily at 9am.  Assume sertraline has a bioavailability of 75% and half-life of 6 hours. What percentage of the administered dose would be remaining in the body 24 hours after Ms. E. took the dose? Answer to 1.d.p.

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QUESTION 4 – HALF LIFE

• Mrs. K. is receiving an infusion of carbetocin after a caesarean section. After dose administration, a nurse found her plasma concentration to be 135nanograms/ml . Assuming carbetocin has a half life of 8 hours, calculate the plasma concentration of carbetocin in mg/L after four half lives.
• ANSWER TO 2.D.P

HALF-LIFE 5

Mrs. F. was administered an injection of gentamicin. The plasma concentration immediately after administration was found to be 4.8mg/L.

Calculate how many half lives it would take to reach approximately 0.0749mg/L from initial plasma concentration.

HALF LIFE - QUESTION 6

• Patrick a 68-year-old patient weighs 60kg and is to be treated with carbamazepine injection once a day for neuropathic pain. The target plasma concentration is 12mg/ Litre.
• Formula CP = dose x s

F x T

Cp = Desired peak conc of drug

F = Bioavailability (1 )

S = Salt factor is 1

T = time interval in hours

Half-life = 20 hours

Using the bioavailable amount(dose which reaches bloodstream), state how many half-lives it will take to have 9mg left in the body.

ANSWER 1- HALF LIFE

• 100MG = 100%
• 100mg/2 = 50mg = 50%
• 50mg/2 = 25mg = 25%
• 25mg/2 = 12.5mg = 12.5%
• 12.5/2 = 6.25mg = 6.25%

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• ANSWER = 4 HALF-LIVES

ANSWER 2 – HALF LIFE

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• 400/2
• 200/2
• 100/2
• 50/2
• 25/2
• 12.5/2
• 6.25/2
• Etc etc etc until 0.01g
• ANSWER = 90 hours

ANSWER 3 - HALF LIFE

• 200mg = 100 %
• But 150mg is bioavailability
• 75– 6 hours
• 37.5 – 6 hours
• 18.75 - 6 hours
• 9.375 - 6 - hours
• 4.7% ANSWER

ANSWER 4 – HALF LIFE

• 135 – TIME 0
• 67.5 – TIME 8 HRS
• 33.75- TIME 16 HRS
• 16.875 – TIME 24 HOURS
• 8.4375 – TIME 32 HOURS
• Hence 8.4375 nanograms/ ml
• Change from nanograms to milligrams by dividing by 1000 000
• 0.000008437mg
• Then convert to mg per litre by multiplying by 1000
• 0.008437mg/L
• ANSWER = 0.01MG/L

ANSWER HALF-LIFE 5

4.8mg/L = 0

2.4mg/L= 1

1.2mg/L = 2

0.6mg/L= 3

0.3mg/L= 4

0.15mg/L = 5

0.0075mg/L = 6

• ANSWER = 6 HALF LIVES

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ANSWER 6 - HALF LIFE

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• Formula cp = d x S

F x T

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• 12 = dose x 1

1 x 24

• rearrange the equation
• 288 = dose x 1
• Dose = 288
• ANSWER = 288 mg/2/2/2/ 2/2= 9mg
• ANSWER = 5 half-lives

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