[2016 ][Greenlight] Calculations Mock Exam Answers PDF

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Green Light Pre-Reg Study Day Programme Mock Exam – Paper 1 February 2016 ANSWERS 1. Mr Thomas is one of your regular patients, who was diagnosed 12 months ago with prostate cancer. His GP has prescribed him Suprefact® injection (buserelin acetate) at a dose of 500mcg BD, and to be reviewed in 28 days. How many vials, to the nearest whole vial, would be required for the first 3-weeks of treatment? (Suprefact® comes in a 5.5mL vial containing 1mg/mL)

4 vials Working 500mcg BD = 1,000mcg = 1mg daily 1mg x 21 days = 21mg The vial contains 1mg/mL, therefore 21mg = 21mL needed for 3 weeks of treatment 21mL/5.5mL = 3.81 vials = 4 vials

2. You have been asked to prepare 300mL of a solution of miglustat concentrate, which when diluted with water 1 in 10, produces a 1 in 1,000 solution. You have in stock a 500mL bottle of concentrate, which contains miglustat 20%. Calculate what volume of concentrate is required to complete the order. 15mL

Working Diluted solution = 1 in 1,000, which has been diluted 10 times. The concentrate is therefore 10 times stronger than this, i.e. 1 in 100 You need 300mL of concentrate, therefore if 1g in 100ml, then 3g in 300mL The product is a 20% strength, which is 20g in 100mL. You need 3g, which will be in 15mL

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3. Ms K is given an intravenous dose of a drug, and her peak serum level is found to be 100 micrograms/mL. When checked 4 hours later, her serum concentration is found to be 1.5625 mg/L. What is the elimination half-life (t1/2) of the drug in Ms K? (You may assume that the distribution is complete and that the elimination is described by a first-order process.) 40 minutes Working 100micrograms/mL, after 2 hours this reduced to 1.5625mg/L 1.5625mg/L = 1562.5micrograms/L = 1.5625 micrograms/mL 100 – t1/2 – 50 – t1/2 – 25 – t1/2 – 12.5 – t1/2 – 6.25 – t1/2 – 3.125 – t1/2– 1.5625 6 half-lives in 4 hours (240mins) therefore 240mins = 40mins 6

4. Mrs SA is 1.65m tall and has been started on orlistat, which has been helping her to lose weight. She initially weighed 88 kg, and has now managed to lose 4.4lbs each month for the last 10 months. What will Mrs SA’s BMI be at her new weight? (round up to the nearest whole number) 25 Working Body mass index (BMI) = weight (kg) height (m2)

2.2 lbs = 1kg

4.4 lbs x 10 months = 44 lbs 44 lbs ÷ 2.2 = 20kg 88kg - 20kg = 68kg BMI = 68kg ÷ 1.652 = 25

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5. Miss A is currently on a heparin infusion. It’s 4.30pm and you notice her pump is bleeping showing an occlusion and she presses the ‘stop’ button. The SHO walks onto the ward and asks you how much heparin she has had so far today. The last rate set on the pump was 1.5mL/hour and it had not altered since it was set up at 7am. Her prescription reads 25,000 units in 50mL sodium chloride 0.9%. How many units of heparin has Miss A received? 7,125 units

Working 7am to 4.30pm = 9.5 hours Rate set is 1.5mL per hour therefore 14.25mL has been administered Product contains 25,000 units in 50mL, therefore X units in 14.25mL X units = 25,000units x 14.25mL 50mL = 7,125units

6. You receive a prescription for 3.75% w/w sulphur in aqueous cream from a patient who has recently attended a dermatology clinic. What weight of sulphur will you need to make 215g of the cream?

8g Working 1 3.75% w/w = 3.75g/100g = Xg in 215g Xg = 3.75g x 215g 100g Xg = 8g Working 2 3.75g x 2.15 = 8g

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7. An elderly patient in one of your local care homes is to be given methotrimeprazine for restlessness. It has been calculated that the Vd (volume of distribution) of methotrimeprazine is 25 L/kg. It is also estimated to have a half-life of 15 hours and an effective bioavailability of 85% when given IM. The patient weighs 80 kg and is administered a dose of 50 mg in 2mL by intramuscular injection. Assuming the patient is not administered any further doses, what would be the approximate blood concentration (in mcg/L) after 75 hours? Give your answer to three decimal places. 0.664 mcg/L Working 85% bioavailability means 50mg x 0.85 = 42.5mg (42,500 mcg) available. Vd = 25L x 80kg = 2,000 L Therefore the concentration will be 42,500 mcg/2,000 L = 21.25mcg/L At hour 0, there will be 21.25 mcg/L At hour 15, there will be: 10.625 mcg/L At hour 30, there will be: 5.3125 mcg/L At hour 45, there will be 2.656 mcg/L At hour 60, there will be 1.328 mcg/L At hour 75, there will be 0.664 mcg/L

8. Miss F presents at the Accident and Emergency department of your hospital having a severe asthma attack, and is prescribed salbutamol to be given as an intravenous infusion. The prescription states that 5mg of salbutamol solution should be diluted to 500 mL with glucose 5%, and given at a rate of 5mcg/min. What is the %w/v concentration of the salbutamol infusion that she will receive?

0.001%w/v

Working The prepared salbutamol infusion contains 5 mg in 500 mL  1 mg in 100 mL  0.001 g in 100 mL  0.001% w/v

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9. You receive a prescription for Sectral® (acebutolol) capsules for a child at a dose of 6.25mg QDS, for 30 days. The only preparation you have available is Sectral® 25mg capsules, with each capsule weighing 75mg. You discuss with the paediatrician and agree to extemporaneously prepare each dose as a 200mg powder, using lactose as a filler. Assuming the weight of the capsule casing is negligible, what weight of lactose will you require to prepare the full quantity of powders? (Round your answer to one decimal place)

21.8 g Working Each powder weighs 200mg and a 25mg Sectral® capsule weighs 75mg 6.25mg QDS = 25mg daily, therefore one Sectral® capsule (containing 25mg acebutolol) will be needed for each daily dose 1 capsule weighs 75mg, therefore the amount in a single dose will be a quarter of this i.e. 18.75mg Each powder will therefore contain 200mg – 18.75mg = 181.25mg lactose per dose So the total weight of lactose will be: 181.25mg x 4 = 725mg x 30 days = 21,750mg = 21.8g

10. You receive a phone call from your local GP, who would like to prescribe metronidazole gel to a patient, and is wondering if the gel formulation is available. You explain to him there is a cream available, called Acea®, which contains metronidazole 0.75%. What weight of metronidazole is present in 40g of Acea cream?

300 mg Working Acea cream contains metronidazole 0.75% ∴ 0.75 g in 100 g ∴ 750 mg in 100 g ∴ 750 mg ÷ 2.5 = 300 mg in 40g

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11. Mr HA brings you a prescription for 2.8% w/w sulphur in aqueous cream. You are required to supply 1,075g. What weight of sulphur will you need to make 1,075g? (give your answer to 2 decimal places)

0.03kg Working 2.8g in 100g = Xg in 1,075g Xg = 2.8g x 1,075g 100g = 30.1g = 0.03kg

12. A child weighing 6.6kg is prescribed a dose of 0.012g/kg/day ciprofloxacin, to be given by i.v. infusion in 2 divided doses. What is the correct volume of ciprofloxacin infusion 2mg/mL that should be given for each dose, rounded to the nearest mL?

20mL

Working 0.012g X 6.6 kg = 0.0792g = 79.2mg per day Infusion is 2mg/mL = 79.2mg in XmL XmL = 79.2mg = 39.6mL 2mg Therefore 39.6 mL is required as a total daily dose, which is 19.8mL, or 20mL to the nearest mL, per dose

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13. You have been asked by the cardiologist during a ward round help calculate a digoxin dose. The patient is a 62-year-old female with a body weight of 71kg, and she needs to receive an oral loading dose of digoxin. You know that the volume of distribution (Vd) per kg body weight is 8L, the salt factor (S) = 1 and the bioavailability (F) = 0.9. What dose should be used to achieve a target plasma concentration (Cp) of 1.75 mcg/L? Round your answer to the nearest whole number. Loading dose = (Vd x Cp) (S x F) 1,104 mcg Working Vd = 8L x 71kg = 568L Loading dose = (Vd x Cp) (S x F) = 568L x 1.75mcg/L 1 x 0.9 = 1,104mcg 14. A doctor has prescribed folic acid for a 3-month-old infant. The infant weighs 6kg, and the dose prescribed is 500mcg/kg/day. The folic acid syrup you have in stock contains 62.5mg of folic acid per 125mL. What volume of this syrup should be given daily?

6mL Working 500mcg x 6kg = 3,000mcg = 3mg Syrup available contains 62.5mg/125mL Therefore there is 3mg in XmL XmL = 3mg x 125mL = 6mL. 62.5mg

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15. A patient who has been taking tadalafil 10mg tablets, has been advised by his doctor to stop taking them due to his recent myocardial infarction. Bearing in mind tadalafil has a half-life of 17.5 hours, if the patient takes one more tablet and then stops, how long will it take until his blood concentration falls to 25% of its maximum level? (round answer to nearest whole number) 35 hours Working Each half-life is 17.5 hours. After 1 half-life, the blood levels will have fallen by 50%, after the 2nd half-life, they will have fallen by another 50% i.e. it will have reduced by 75% of the maximum level 2 half-lives = 35 hours

16. A 70–year-old male patient has been prescribed cimetidine 200mg, and the doctor has contacted you to confirm that he has prescribed an appropriate dose. With reference to the clinical records, you note that his serum creatinine is 0.15micromol/mL, he weighs 53kg and his height is 1.63m. The current policy in your hospital is to use the Cockcroft and Gault formula to assess renal function. Excerpt from BNF: Renal impairment reduce dose; 200 mg 4 times daily if eGFR 30– 50 mL/minute/1.73 m2; 200 mg 3 times daily if eGFR 15–30 mL/minute/1.73 m2; 200 mg twice daily if eGFR less than 15 mL/minute/1.73 m2; occasional risk of confusion Taking his renal impairment into consideration, how many times a day should the patient receive cimetidine 200mg? Four times a day Working CrCl (mL/min)

=

(140 – 70yrs) × 53kg × 1.23 Serum Creatinine (micromol/L)

CrCl = 30.422 (units for serum creatinine need to be changed to micromole/L). Looking at the BNF excerpt, the frequency should be 200mg four times a day

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17. You are working for a pharmaceutical company where you are required to calculate the weight of potassium chloride in large amounts of solution before it is prepared. How many grams of potassium chloride are needed to prepare 2.5L of a solution containing 12 mmol of potassium ions per 10mL? (round your answer to the nearest whole number) [atomic weight of potassium = 39; atomic weight of chlorine = 35.5]

224g

Working 1 mole of potassium chloride weighs 74.5 g 1 mmol = 74.5 mg The solution to be prepared contains 12 mmol potassium ions in 10mL = 120mmol in 100mL = 3,000 mmol in 2,500mL Mass (g) = Mr x Moles = 74.5mg x 3mol = 223.5g

18. You receive a private prescription for a patient and need to calculate how many bottles of eye drops the patient will need to fully complete his regimen described below. How many 5mL bottles of dexamethasone 0.1% eye drops will the patient need, if they use the same bottle of eye drops for both eyes? (15 drops = 1mL) Rx: Dexamethasone 0.1% eye drops Put 2 drops into each eye every 30 minutes for 12 hours Then put 2 drops into each eye QDS for 24 hours Then put 2 drops into each eye TDS for a further 6 days Then put 2 drops into each eye BD for a further 7 days

4 bottles Working Total number of drops needed: 96 + 16 + 72 + 56 = 240 drops for both eyes 15 drops = 1mL, therefore for 240 drops you will need 16mL (240/15) = 4 bottles (3 bottles is closest number, but wouldn’t allow patient to complete the course)

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19. You receive a call from a doctor on the Paediatric Unit who would like you to double check her calculation for a dopamine infusion she is prescribing for a neonate weighing 2.6kg. She is going to ask the nursing staff to dilute the dopamine 45mg/kg body-weight to a final volume of 50mL with glucose 5%. She would like to know at what rate she should run this infusion to provide a dose of 3 micrograms/kg/minute?

0.2 mL/hour

Working 45mg/kg  45mg x 2.6kg = 117mg 117mg diluted to 50mL glucose  117mg/50mL Dose = 3 microgram/kg/minute = 3mcg x 2.6kg = 7.8 microgram/minute = 468 microgram/hour Infusion is Which = i.e. Therefore

117mg/50mL 11.7mg/5mL 11,700 microgram/5mL 468 micrograms/XmL XmL = 468mcg x 5mL 11,700mcg XmL = 0.2mL/hour

20. Mr ST is 55 years old and is concerned that he is overweight. You ask him for his height and weight in order to calculate his Body Mass Index. He tells you he weighs 68kg and is 160cm tall. According to Mr ST’s BMI, state whether it is TRUE or FALSE that he is overweight.

TRUE

Working BMI = 68kg / 1.62 = 26.56 A BMI greater than 25kg/m2 indicates that a patient is overweight Answer = TRUE

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21. A cream contains the following ingredients: Propylene Glycol PhEur 39.5% Fractionated Coconut Oil PhEur 26.5% Sodium Hydroxide PhEur 0.75% Purified Water PhEur to 100% What is the weight of Fractionated Coconut Oil PhEur needed to produce 95.5kg of the cream?

25.3 kg Working Fractionated Coconut Oil PhEur 26.5% = 26.5g in 100g = 265g in 1,000g (1kg) Xg in 95.5kg Xg = 265g x 95.5kg 1kg Xg = 25,307.5g = 25.3kg

23. A baby has been prescribed Gaviscon Infant powder sachets, one dose three times a day with feeds for 2 days, and then reduce to twice a day. How many mmol of sodium ions will the baby receive in 144 hours? Round your answer to 1 decimal point

Gaviscon Infant Powder Sachets = 0.92mmol Na/dose 12.9mmol

Working BNF: Gaviscon Infant Powder Sachets = 0.92mmol Na / dose Amount Na = 0.92mmol x 3 = 2.76mmol x 2 days = 5.52mmol 0.92mmol x 2 = 1.84 mmol x 4 days = 7.36mmol Total Na ions: 12.88mmol

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24. Baby KC weighs 15kg and has been prescribed baclofen liquid, which is available as a 5mg/5mL solution. The treatment regimen is as follows: 1.5mg/kg for 15 days, then 2.0mg/kg for 6 days, then 2.5mg/kg for 7 days. What volume of baclofen liquid would be needed to complete the course of treatment?

Working 1.5mg x 15kg x 15 days = 337.5mg 2mg x 15kg x 6 days = 180mg 2.5mg x 15kg x 7 days = 262.5mg Total = 780mg

780mL

Baclofen liquid = 5mg/5mL  1mg/1ml We therefore need 780mL

25. An elderly patient on your ward has been diagnosed with pneumonia and needs to be prescribed co-amoxiclav. He also suffers from chronic kidney disease and his serum creatinine is currently 187 µmol/L. He is 82 years old and only weighs 56 kg. Use the Cockcroft & Gault formula to calculate his creatinine clearance. Give your answer to two decimal places. 21.36 mL/min

Working CrCl = (140-age) x weight x F (1.04 female, 1.23 male) / Serum Cr CrCl = (140-82) x 56kg x 1.23 / 187µmol/L = 3,995.04 / 187 = 21.36 mL/min

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26. Whilst working in a specials manufacturing unit, you receive an order for 45g of hydrocortisone cream 1.5%. Your pharmacy only has the 1% and 2.5% formulations available. How many grams of each cream will you need, in order to make the required cream? 15g of 2.5 %

30g of 1 %

Working Can use allegation method here: 2.5%

0.5

0.5 parts 2.5% cream

1.5% 1%

1.5 parts in total 1

1 parts 1 % cream

Need to make up 45g so 45 g ÷ 1.5 parts = 30 g/part. Therefore: 30 g/part x 0.5 parts = 15g 2.5% cream to be used. Therefore 30g 1% cream. Can also use algebraic method (or trial and error) Alternative way of calculating: We want 45g of 1.5% (1.5g/100g) Hc = 0.675g of Hc We have available 2.5% and 1% 2.5% = 2.5g/100g = 0.25g/10g = 0.375g/15g 1% = 1g/100g = 0.1g/10g = 0.3g/30g

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27. One of your regular patients, Mr JL, presents with a prescription at your pharmacy for prednisolone 30mg daily. He also shows you his discharge letter following a recent stay in hospital, from which he was discharged this morning. An excerpt from the discharge summary is shown below: Rx. Prednisolone 5mg tablets Continue with 30mg daily as directed for 2 days, then reduce by 5mg every three days until stopped.

How many 2.5 mg prednisolone tablets should you supply to ensure Mr JL can complete his reducing course?

114 tablets

Working Dose 30 mg 25 mg 20 mg 15 mg 10 mg 5 mg

No. Days 2 3 3 3 3 3

No. tabs per day 12 10 8 6 4 2 Total

Total No. Tabs 24 30 24 18 12 6 114

28. You are discussing a 6-year-old patient’s newly prescribed medication with a nurse in the oncology ward. The patient weighs 19 kg and is 112 cm tall. He is prescribed dactinomycin 350 mcg/m2. Dactinomycin is available as a lyophilised powder in vials which is reconstituted by adding 1.1 mL of water for injections. The resultant solution is 0.5 mg per mL. Formula for Body Surface Area

Using the formula above, what volume of Dactinomycin is needed per dose? Give your answer to two decimal places. 0.54mL Working BSA = √[(112cm x 19kg)/3600] = 0.768 m2 350mcg x 0.768m2 = 268.8 mcg 500mcg in 1mL 268.8mcg in XmL XmL = 268.8mcg x 1mL = 0.54mL 500mcg

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29. Potassium permanganate is often available as a concentrate that requires dilution and its final strength is usually expressed as a ratio. What is the percentage strength of the concentrate if it requires a 1 in 35 dilution to produce a 1 in 5000 final solution? Give your answer to 1 decimal place

0.7 %

Working Diluted solution is 1 in 5000, and we know the original concentrate is 35 times stronger. The concentrate must therefore be 1 in 5000 = 1 in 142.857. 35 1g in 142.857mL = Xg in 100mL Xg = 100mL x 1g = 0.7g/100mL = 0.7% 142.857mL

30. You have received a discharge summary from the paediatric ward requesting a lower dose of a drug that is normally only available as 60mg tablets. You decide to make up powders so that these can be sprinkled on the child’s food to disguise the bitter taste. You calculate that you will need to make 10 powders, each weighing 250mg and containing 40mg of drug. You will be using lactose as the diluent. Assuming you need to make a 20% overage, calculate how many tablets (to the nearest whole tablet) and how many grams of lactose (to 2 decimal places) will be required to complete the prescription.

8 tablets

2.52g Working You need to make 10 powders, plus 20% overage = 12 powders 12 powders x 250mg = 3,000mg in total (lactose + drug) 12 powders x 40mg of drug = 480mg in total of drug = 8 x 60mg tablets 3,000mg – 480mg = 2,520mg of lactose needed = 2.52g

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31. Mr P, a 24 year old regular patient, is being treated with chlordiazepoxide for withdrawal in severe alcohol dependence. His consultant wants him to take his daily dose in four divided doses, starting with 200mg for the first two days and then gradually reducing the dose of chlordiazepoxide by 20mg a day for the next 7 days. It has been decided to issue the patient with 10mg tablets. The patient is happy to do this. How many tablets will you need to dispense the full course?

124 tablets Working 200mg for 2 days = 40 180mg for 1 day = 18 160mg for 1 day =16 140mg for 1 day =14 120mg for 1 day = 12 100mg for 1 day = 10 80mg for 1 day = 8 60mg for 1 day = 6 1,240mg over 9 days 1,240mg in 10mg tablets = 124 tablets 32. A customer comes into your pharmacy to ask your advice about a fluoride mouthwash. She has recently moved into the area, and after ...