Practise — drug calculations
Practice questions in drug calculations
Ten questions with step-by-step solutions. Work them out yourself first, then open the solution and compare.
Ten questions
Original practice questions that train the basic principles. Use a calculator and check the units.
1. Tablets
A patient is prescribed 150 mg. The tablets available are 50 mg. How many tablets should be given?
Show solution+
Amount = Dose ÷ Strength = 150 ÷ 50 = 3 tablets. More on this →
2. Oral liquid
The prescription is 200 mg. The liquid contains 40 mg/mL. How many mL should be given?
Show solution+
200 ÷ 40 = 5 mL. More on this →
3. Injection
The prescription is 7.5 mg. The injection contains 10 mg/mL. How many mL should be drawn up?
Show solution+
7.5 ÷ 10 = 0.75 mL. More on this →
4. Dose per kilogram
The prescription is 5 mg/kg. The patient weighs 60 kg and the solution contains 50 mg/mL. How many mL should be given?
Show solution+
Dose = 5 × 60 = 300 mg. Amount = 300 ÷ 50 = 6 mL. More on this →
5. Unit conversion
The prescription is 0.25 mg. The tablets are 125 micrograms. How many tablets should be given?
Show solution+
0.25 mg = 250 micrograms (1 mg = 1000 micrograms). 250 ÷ 125 = 2 tablets. More on this →
6. Percentage solution
The prescription is 100 mg. The solution is 2%. How many mL should be given?
Show solution+
2% = 2 g per 100 mL = 20 mg/mL. 100 ÷ 20 = 5 mL. More on this →
7. Dilution
4 mL of a 50 mg/mL solution is diluted to a total of 20 mL. What is the concentration of the diluted solution?
Show solution+
C1 × V1 = C2 × V2, so 50 × 4 = C2 × 20. C2 = 200 ÷ 20 = 10 mg/mL. More on this →
8. Drops per minute
1000 mL is to be given over 8 hours. The giving set delivers 20 drops per mL. How many drops per minute?
Show solution+
8 hours = 480 minutes. (1000 × 20) ÷ 480 = 41.7, so about 42 drops/min. More on this →
9. Infusion rate
500 mL is to be given over 4 hours by pump. What rate should the pump be set to?
Show solution+
500 ÷ 4 = 125 mL/hour. More on this →
10. Dose spread over the day
The daily dose is 600 mg divided into 3 doses. The tablets are 100 mg. How many tablets per dose?
Show solution+
600 ÷ 3 = 200 mg per dose. 200 ÷ 100 = 2 tablets per dose. More on this →
Frequently asked questions
How do I practise drug calculations?+
Work through questions yourself before you look at the solution, with a calculator, and check the units at every step. Go over your mistakes and practise extra in the areas where you lose marks.
What is the most common source of error in drug calculations?+
Units. Do not mix mg, micrograms and grams, and check whether the strength is given per mL, per tablet or as a percentage before you calculate.
Are the questions on this page real assessment questions?+
No, they are original practice questions that train the same basic principles. Your own assessment may look different, so check your syllabus.
More questions, with answers and statistics
Dos has practice tests of ten questions, a built-in calculator next to each question and statistics for your weak areas.
