Pharmaceutical calculations make up a significant portion of major pharmacy licensing exams worldwide:
- OPRA: Approximately 15–20%
- PEBC: Around 10–15%
- DHA: Typically 10–20%
Sample Pharmaceutical Calculation Problems
Example 1: Dosage Calculation Based on Body Weight
Question:
A patient weighing 70 kg is prescribed a drug at a dose of 5 mg/kg/day. What is the total daily dose?
Solution:
Step 1: Identify the formula- Dose = Body weight × Dose per kg
Step 2: Substitute values
Dose = 70 kg × 5 mg/kg
Step 3: Calculate
Dose = 350 mg/day
Answer: The patient should receive 350 mg per day.
Example 2: IV Flow Rate Calculation
Question:
A 500 mL IV fluid is to be infused over 5 hours. What is the flow rate in mL/hour?
Solution:
Step 1: Use formula- Flow rate = Total volume ÷ Time
Step 2: Substitute values
Flow rate = 500 mL ÷ 5 hours
Step 3: Calculate Flow rate = 100 mL/hour
Answer: The IV should run at 100 mL/hour.
Example 3: Dilution Calculation
Question:
How much stock solution is needed to prepare 100 mL of a 10% solution from a 20% solution?
Solution:
Step 1: Use formula C1 × V1 = C2 × V2
Step 2: Substitute values
20% × V1 = 10% × 100 mL
Step 3: Solve
V1 = (10 × 100) ÷ 20 = 50 mL
Answer: Use 50 mL of stock solution and dilute to 100 mL.