CAOP - Competency Assessment of Overseas Pharmacist Pharmaceutical Calculations Questions and Answers — Questions and Answers
Question 1: A 4-year-old child weighing 16 kg is prescribed paracetamol for fever at a dose of 15 mg/kg. The paracetamol suspension available is 100 mg/5 mL. What volume of the suspension, in mL, should be administered for a single dose?
- 15 mL
- 12 mL (Correct answer)
- 10 mL
- 7.5 mL
Correct answer: 12 mL
First, calculate the total required dose in mg: 16 kg × 15 mg/kg = 240 mg. Next, calculate the volume of the 100 mg/5 mL suspension that contains 240 mg: (240 mg / 100 mg) × 5 mL = 2.4 × 5 mL = 12 mL. Therefore, 12 mL of the suspension should be administered.
Question 2: A patient is to receive 1 litre of 0.9% Sodium Chloride intravenously over a period of 10 hours. What is the required infusion rate in mL/hour?
- 125 mL/hour
- 80 mL/hour
- 100 mL/hour (Correct answer)
- 150 mL/hour
Correct answer: 100 mL/hour
The total volume to be infused is 1 litre, which is equal to 1000 mL. The total time for the infusion is 10 hours. The infusion rate is calculated by dividing the total volume by the total time: Rate = 1000 mL / 10 hours = 100 mL/hour.
Question 3: A pharmacist needs to prepare 300 mL of a 2% w/v hydrocortisone solution using a 10% w/v stock solution. How many millilitres of the 10% stock solution are required?
- 30 mL
- 150 mL
- 60 mL (Correct answer)
- 15 mL
Correct answer: 60 mL
This is a dilution calculation that can be solved using the formula C1V1 = C2V2, where C1 is the initial concentration, V1 is the initial volume, C2 is the final concentration, and V2 is the final volume.
C1 = 10%
V1 = ?
C2 = 2%
V2 = 300 mL
(10%) × V1 = (2%) × (300 mL)
V1 = (2 × 300) / 10
V1 = 600 / 10 = 60 mL.
Question 4: A pharmacist needs to create a 2.5% w/w salicylic acid ointment. They only have 5% w/w and 1% w/w salicylic acid ointments in stock. To make 100 g of the 2.5% ointment, how much of the 5% ointment is needed?
- 62.5 g
- 50.0 g
- 25.0 g
- 37.5 g (Correct answer)
Correct answer: 37.5 g
This problem can be solved using alligation.
1. Set up the tic-tac-toe grid: Higher concentration (5%) top left, lower concentration (1%) bottom left, desired concentration (2.5%) in the middle.
2. Subtract diagonally: |2.5 - 1| = 1.5 parts of the 5% ointment. |5 - 2.5| = 2.5 parts of the 1% ointment.
3. Total parts = 1.5 + 2.5 = 4.0 parts.
4. Calculate the amount of 5% ointment needed: (1.5 parts / 4.0 total parts) × 100 g = 0.375 × 100 g = 37.5 g.
Question 5: A vial contains 1 g of amoxicillin powder with a displacement value of 0.8 mL/g. To prepare a solution with a final concentration of 200 mg/mL, how much Water for Injections (diluent) must be added?
- 5.0 mL
- 4.2 mL (Correct answer)
- 5.8 mL
- 8.0 mL
Correct answer: 4.2 mL
1. Calculate the required final volume: Total drug (1 g = 1000 mg) / Desired concentration (200 mg/mL) = 5 mL.
2. Calculate the volume displaced by the powder: 1 g × 0.8 mL/g = 0.8 mL.
3. Calculate the volume of diluent to add: Required final volume - Powder displacement volume = 5 mL - 0.8 mL = 4.2 mL.
Question 6: How many millimoles (mmol) of sodium are present in a 250 mL intravenous bag of 0.9% w/v Sodium Chloride (NaCl)? (Molar mass of Na = 23 g/mol, Cl = 35.5 g/mol)
- 77.0 mmol
- 154.0 mmol
- 38.5 mmol (Correct answer)
- 22.5 mmol
Correct answer: 38.5 mmol
1. Molar mass of NaCl = 23 + 35.5 = 58.5 g/mol.
2. Calculate the mass of NaCl in the bag: 0.9% w/v = 0.9 g / 100 mL. In 250 mL, the mass is (0.9 g / 100 mL) × 250 mL = 2.25 g.
3. Calculate the moles of NaCl: Mass / Molar mass = 2.25 g / 58.5 g/mol ≈ 0.0385 mol.
4. Convert moles to millimoles: 0.0385 mol × 1000 mmol/mol = 38.5 mmol.
5. Since there is one sodium atom per molecule of NaCl, the millimoles of Na+ are equal to the millimoles of NaCl, which is 38.5 mmol.
