PEBC Pharmaceutical Calculations 1 — Questions and Answers
Question 1: A physician orders amoxicillin 40 mg/kg/day divided every 8 hours for a child weighing 22 kg. How many mg should be given per dose?
- 147 mg
- 293 mg (Correct answer)
- 440 mg
- 880 mg
Correct answer: 293 mg
40 mg/kg/day × 22 kg = 880 mg/day divided into 3 doses (every 8 hours) = 293 mg per dose.
Question 2: A pharmacist needs to prepare 250 mL of a 0.9% NaCl solution. How many grams of NaCl are required?
- 0.9 g
- 2.25 g (Correct answer)
- 9 g
- 22.5 g
Correct answer: 2.25 g
0.9% means 0.9 g per 100 mL; therefore 0.9 × (250/100) = 2.25 g of NaCl are needed.
Question 3: An IV infusion of 1000 mL is to be administered over 8 hours using a drip set delivering 20 drops/mL. What is the drip rate in drops per minute?
- 20 drops/min
- 42 drops/min (Correct answer)
- 36 drops/min
- 28 drops/min
Correct answer: 42 drops/min
1000 mL ÷ 8 hr = 125 mL/hr; 125 mL/hr ÷ 60 min × 20 drops/mL ≈ 42 drops/min.
Question 4: A medication is available as 250 mg/5 mL. A patient needs a 375 mg dose. How many mL should be dispensed?
- 5 mL
- 7.5 mL (Correct answer)
- 10 mL
- 12.5 mL
Correct answer: 7.5 mL
Using proportion: 375 mg × (5 mL / 250 mg) = 7.5 mL.
Question 5: How many milligrams of drug are contained in 2 L of a 1:5000 solution?
- 200 mg
- 400 mg (Correct answer)
- 100 mg
- 250 mg
Correct answer: 400 mg
1:5000 means 1 g per 5000 mL = 0.2 mg/mL; 0.2 mg/mL × 2000 mL = 400 mg.
Question 6: A patient is to receive heparin 25,000 units in 250 mL NS at 1,200 units/hour. What is the correct infusion rate in mL/hour?
- 8 mL/hr
- 10 mL/hr
- 12 mL/hr (Correct answer)
- 15 mL/hr
Correct answer: 12 mL/hr
Concentration = 25,000 units ÷ 250 mL = 100 units/mL; 1,200 units/hr ÷ 100 units/mL = 12 mL/hr.
Question 7: What is the percentage strength (w/v) of a solution made by dissolving 5 g of drug in enough water to make 200 mL?
- 1%
- 2.5% (Correct answer)
- 4%
- 5%
Correct answer: 2.5%
Percentage (w/v) = (grams of solute / mL of solution) × 100 = (5 / 200) × 100 = 2.5%.
PEBC Pharmaceutical Calculations 1
A physician orders amoxicillin 40 mg/kg/day divided every 8 hours for a child weighing 22 kg.
How many mg should be given per dose?