CPhT Dosage Calculations 2

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?

Accepted Answer

10 mL

Answer

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?

Accepted Answer

10 mL/hr

Answer

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?

Accepted Answer

293 mg

Answer

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?

Accepted Answer

25 mL

Answer

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?

Accepted Answer

4 tablets

Answer

1 g = 1,000 mg; each dose = 1,000 mg ÷ 500 mg = 2 tablets; twice daily = 4 tablets/day.

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