calcs Flashcards
(10 cards)
A 38-year-old woman is being treated for alcohol withdrawal symptoms at a private clinic.
She is prescribed diazepam on a private prescription. It is to be taken daily in divided doses, starting with 30 mg daily for the first three days, and then gradually reducing the dose of diazepam by 5 mg every three days until she stops.
The best price for a pack of diazepam 5 mg, 28 tablets, is £1.89.
Private prescriptions in your pharmacy are priced using the following formulae:
Cost + 25% markup + £6.50 dispensing fee
How much will the prescription cost, in pounds?
Give your answer to the nearest one pound
Step 1 - Calculate how many tables you will need to supply
30 mg (6 tabs) for 3 days = 18 tablets
25 mg (5 tabs) for 3 day = 15 tablets
20 mg (4 tabs) for 3 day = 12 tablets
15 mg (3 tabs) for 3 day = 9 tablets
10 mg (2 tabs) for 3 day = 6 tablets
5 mg (1 tabs) for 3 day = 3 tablets
Total = 63 tablets needed
Step 2 - Calculate the cost
Cost per tablet is £1.89 / 286.75 pence per tablet
Cost for 63 tablets = 425.25 pence = £4.2525
£4.2525 x 1.25 (25% markup) = £5.32 + £6.50 dispensing fee = £11.82
£12 is the nearest whole pound
Assessment topic: Health Economics
The correct answer is: 12
A patient weighing 82 kg is administered a dose of 50 mg in 2 mL levomepromazine by intramuscular injection.
It has been calculated that the volume of distribution of levomepromazine is 15 L / kg.
It is also estimated to have a half-life of 20 hours and an effective bioavailability of 80% when given by intramuscular injection.
If the patient is not administered any further doses, what is the blood concentration in mcg / L after 60 hours?
Give your answer to one decimal place.
80% bioavailability means 50 x 0.8 = 40 mg (40,000 mcg) available
Volume of distribution = 15 x 82 = 1230 L
Therefore, the concentration will be 40000 mcg ÷ 1230 L
Which is 32.52 mcg / L
Then calculate half-life:
At hour 0, there will be 32.52 mcg / L
At hour 20, there will be 16.26 mcg / L
At hour 40, there will be 8.13 mcg / L
At hour 60, there will be 4.065 mcg / L
Assessment topic: Pharmacokinetics
The correct answer is: 4.1
A 49-year-old man has chronic back pain which has worsened over the last six months. Today 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.
Information from the BNF about equivalent doses of opioid analgesics has been provided below.
https://bnf.nice.org.uk/guidance/prescribing-in-palliative-care.html
How many milligrams of morphine sulfate will the patient require every six hours?
Give your answer to one decimal place
Using the table provided in the extract identify how many mg of codeine is equivalent to oral (PO) morphine.
100 mg of codeine = 10 mg of PO morphine.
The patient is taking 6 x 30 mg of codeine tablets per day = 180 mg of codeine per day.
180 mg /10 = 18 mg of PO morphine per day.
24 hours / 6 hourly administration = 4
18 mg / 4 = 4.5 mg of morphine every six hours.
Assessment topic: Doses and dose regimens - Extract
The correct answer is: 4.5
A local vet has placed an order with you for an antiseptic solution for use when carrying out minor surgical procedures.
The vet requires 4.75 litres of a 1.75% w / v solution. You have in stock a solution of 12.25% w / v antiseptic solution and decide to dilute this.
What volume of 12.25% w / v stock solution will be required to produce sufficient antiseptic solution for use by the vet?
Give your answer to the nearest 5 mL
You have a 12.25% w/v solution, and you need to make 4.75 litres of a 1.75% w/v solution.
C1 x V1 = C2 x V2
12.25 % x V1 = 1.75% x 4,750 mL
V1 = 1.75% x 4,750 mL = 678.5714 mL = 680 mL to the nearest 5 mL
12.25%
Assessment topic: Dilutions
The correct answer is: 680
A 60-year-old man weighing 62 kg is administered oxazepam for the treatment of insomnia associated with anxiety. They are given a dose of 15 mg once at bedtime. Immediately after administration the plasma level of oxazepam is measured at 75 mcg / mL.
The half-life of oxazepam is 10 hours.
What is the plasma concentration in mcg / mL after 1,800 minutes?
Give your answer to two decimal places
Step 1 - Calculate 1800 mins in hours:
1800 / 60 = 30 hours
Step 2 – Calculate half-lives in 30 hours (use a table to help):
Time (hours)
Serum Concentration mcg / mL
0
75
10
37.5
20
18.75
30
9.375
The answer to two decimal places is 9.38 mcg / mL
Assessment topic: Pharmacokinetics
The correct answer is: 9.38
A 32-year-old man, who is used to drinking almost 30 units of alcohol daily, has been admitted to hospital to receive alcohol detoxification support to help avoid potentially fatal withdrawal symptoms.
He is treated with a fixed dose schedule of chlordiazepoxide as described below:
Day 1: 30 mg four times a day
Day 2: 30 mg at 8am and 10pm, 20 mg at 12 noon and 6pm
Day 3: 20 mg four times a day
Day 4: 20 mg at 8am and 10pm, 10 mg at 12 noon and 6pm
Day 5: 10 mg four times a day
Day 6: 10 mg twice daily
Day 7: 10 mg once daily
You have chlordiazepoxide 10 mg capsules available.
How many chlordiazepoxide 10 mg capsules are needed to complete this course?
Consider the number of capsules taken at each dose and then the number of times a day
Day 1: (3 capsules x 4) = 12
Day 2: (3 capsules x 2) + (2 capsules x 2) = 10
Day 3: (2 capsules x 4) = 8
Day 4: (2 capsules x 2) + (1 capsule x 2) = 6
Day 5: 1 capsule x 4 = 4
Day 6: 1 capsule x 2 = 2
Day 7: 1 capsule x 1 = 1
Total needed = 12 + 10 + 8 + 6 + 4 + 2 + 1 = 43 capsules
Assessment topic: Doses and dose regimens
The correct answer is: 43
A dermatologist has contacted you regarding one of his patients in the burns unit, who requires a gelatin infusion.
He would like to make up a 120 mL infusion containing a 1 in 4 gelatin 7% in dextrose 5% solution.
What volume, in mL, of gelatin 7% will be needed to prepare the required infusion?
1 in 4 = 4 parts
120 mL / 4 = 30 mL / part
Which is 30 mL gelatin 7% and 90 mL dextrose 5% (total of 120 mL infusion)
30 mL of gelatin 7% required
Assessment topic: Concentrations
The correct answer is: 30
You are working in a pharmaceutical laboratory and have a stock solution of a new drug with a concentration of 35% w/v.
The drug is used as a mouth wash at a concentration of 0.35% w/v. You are requested to prepare 50 mL of a solution of intermediate strength, such that those trialling the mouthwash will dilute this solution 1 in 9 to get the correct concentration immediately before use.
What would be the concentration of the intermediate solution?
Give you answer to the nearest whole number
The new drug is used as a mouthwash at a concentration of 0.35% w/v.
If this has been made from a solution that has been diluted 1 in 9, multiplying by 9 will give you the concentration of the intermediate solution.
0.35 x 9 = 3.15, round to 3% w/v
Assessment topic: Dilutions
The correct answer is: 3
A baby has been started on phenobarbital 15 mg / 5 mL elixir at the maximum dose and as a result has experienced fewer seizures. The baby weighs 7.8 kg.
https://www.medicines.org.uk/emc/product/4920/smpc#gref
The baby has now developed liver impairment. What is the concentration of ethanol received each day?
Give your answer to the nearest whole number.
The baby has been started on the maximum dose; 6 mg x 7.8 kg = 46.8 mg each day.
The extract tells you that each 5 mL of phenobarbital contains 1.6 g of ethanol.
To work out how many mL of phenobarbital the patient will receive:
46.8 mg/15 mg = 3.12 mL x 5 = 15.6 mL
5 mL = 1.6 g of ethanol therefore:
15.6 mL/5 x 1.6 g = 4.992 g of ethanol
4.992 g/15.6 mL = 0.32
0.32 x 100 = 32% w/v
Assessment topic: Concentrations – extract & paediatrics
The correct answer is: 32
