CPhT Dosage Calculations 2 — Questions and Answers
Question 1: A patient requires 0.5 mg of a drug available as 0.25 mg/5 mL oral solution. How many mL should be dispensed per dose?
- 5 mL
- 10 mL (Correct answer)
- 2.5 mL
- 20 mL
Correct answer: 10 mL
0.5 mg ÷ 0.25 mg × 5 mL = 10 mL per dose.
Question 2: A physician orders heparin 25,000 units in 250 mL NS to infuse at 1,000 units/hr. What is the flow rate in mL/hr?
- 5 mL/hr
- 10 mL/hr (Correct answer)
- 15 mL/hr
- 20 mL/hr
Correct answer: 10 mL/hr
Concentration = 25,000 units ÷ 250 mL = 100 units/mL; 1,000 units/hr ÷ 100 units/mL = 10 mL/hr.
Question 3: A child weighing 22 kg needs amoxicillin 40 mg/kg/day divided every 8 hours. How many mg per dose?
- 220 mg
- 293 mg (Correct answer)
- 880 mg
- 440 mg
Correct answer: 293 mg
22 kg × 40 mg/kg = 880 mg/day ÷ 3 doses = 293.3 mg per dose.
Question 4: An IV bag contains 1 g of drug in 100 mL. The order is to give 250 mg. How many mL should be administered?
- 10 mL
- 25 mL (Correct answer)
- 40 mL
- 50 mL
Correct answer: 25 mL
1 g = 1,000 mg; 250 mg ÷ 1,000 mg × 100 mL = 25 mL.
Question 5: A patient is prescribed metformin 1 g twice daily. The tablets available are 500 mg each. How many tablets per day?
- 2 tablets
- 4 tablets (Correct answer)
- 3 tablets
- 1 tablet
Correct answer: 4 tablets
1 g = 1,000 mg; each dose = 1,000 mg ÷ 500 mg = 2 tablets; twice daily = 4 tablets/day.
Question 6: Dopamine 400 mg is added to 250 mL D5W. The order is 5 mcg/kg/min for a 70 kg patient. What is the infusion rate in mL/hr?
- 6.6 mL/hr
- 13.1 mL/hr (Correct answer)
- 3.3 mL/hr
- 26.2 mL/hr
Correct answer: 13.1 mL/hr
Dose = 5 mcg/kg/min × 70 kg = 350 mcg/min = 21,000 mcg/hr = 21 mg/hr; concentration = 400 mg ÷ 250 mL = 1.6 mg/mL; 21 mg/hr ÷ 1.6 mg/mL ≈ 13.1 mL/hr.
Question 7: A drug is available as a 2% w/v solution. How many grams of drug are in 500 mL of this solution?
- 1 g
- 5 g
- 10 g (Correct answer)
- 20 g
Correct answer: 10 g
2% w/v = 2 g per 100 mL; 2 g × 5 = 10 g in 500 mL.
CPhT Dosage Calculations 2
A patient requires 0.5 mg of a drug available as 0.25 mg/5 mL oral solution.
How many mL should be dispensed per dose?