CPhT Dosage Calculations 3 — Questions and Answers
Question 1: A nurse requests 250 mL of a 0.9% NaCl solution. How many grams of NaCl are needed to prepare this solution?
- 0.9 g
- 2.25 g (Correct answer)
- 9 g
- 4.5 g
Correct answer: 2.25 g
0.9% = 0.9 g/100 mL; 0.9 × 2.5 = 2.25 g in 250 mL.
Question 2: An order reads: Morphine 2 mg IV q4h PRN pain. The vial contains 10 mg/mL. How many mL per dose?
- 0.1 mL
- 0.2 mL (Correct answer)
- 0.5 mL
- 2 mL
Correct answer: 0.2 mL
2 mg ÷ 10 mg/mL = 0.2 mL per dose.
Question 3: A pharmacy receives an order for KCl 20 mEq in 100 mL NS. Stock vials contain 2 mEq/mL. How many mL of KCl should be added?
- 5 mL
- 10 mL (Correct answer)
- 20 mL
- 40 mL
Correct answer: 10 mL
20 mEq ÷ 2 mEq/mL = 10 mL of KCl stock.
Question 4: A patient weighing 88 lbs needs a drug dosed at 10 mg/kg. What is the correct dose in mg?
- 400 mg (Correct answer)
- 880 mg
- 4,000 mg
- 400 mg
Correct answer: 400 mg
88 lbs ÷ 2.2 = 40 kg; 40 kg × 10 mg/kg = 400 mg.
Question 5: How many 250 mg capsules are needed to fill a prescription for amoxicillin 500 mg TID for 10 days?
- 30 capsules
- 60 capsules (Correct answer)
- 20 capsules
- 45 capsules
Correct answer: 60 capsules
500 mg ÷ 250 mg = 2 capsules/dose × 3 doses/day × 10 days = 60 capsules.
Question 6: A TPN order calls for 500 mL of 70% dextrose and 500 mL of 10% amino acids. What is the final dextrose concentration in the combined 1,000 mL bag?
- 35% (Correct answer)
- 40%
- 70%
- 80%
Correct answer: 35%
500 mL × 70% = 350 g dextrose; 350 g ÷ 1,000 mL × 100 = 35%.
Question 7: An order is for vancomycin 15 mg/kg IV q12h. Patient weighs 68 kg. Available vials are 500 mg/10 mL. How many mL per dose?
- 10.2 mL
- 20.4 mL (Correct answer)
- 15 mL
- 30 mL
Correct answer: 20.4 mL
15 mg/kg × 68 kg = 1,020 mg; 1,020 mg ÷ 500 mg × 10 mL = 20.4 mL.
CPhT Dosage Calculations 3
A nurse requests 250 mL of a 0.9% NaCl solution.
How many grams of NaCl are needed to prepare this solution?