A drug order is 1.5 mg/kg to be infused over 6 hours. The patient weighs 20 kg. The drug solution is 0.5 mg/mL. What is the infusion rate in mL/hr?

• A. 60 mL/hr
• B. 30 mL/hr
• C. 120 mL/hr
• D. 15 mL/hr

Answer: (A)

When a dose is given based on weight but specifies a total infusion time, first convert the weight-based dose to a total amount, then translate that total dose into a flow rate using the concentration.

Compute the total dose: 1.5 mg/kg times 20 kg equals 30 mg to be given over 6 hours.

Find the hourly dose: 30 mg divided by 6 hours equals 5 mg per hour.

Use the solution concentration to turn mg/hour into mL/hour: 5 mg/hour divided by 0.5 mg/mL equals 10 mL/hour.

So the infusion rate should be 10 mL per hour. If you misread the instruction as 1.5 mg/kg per hour over 6 hours, you’d get 60 mL/hour, but the order specifies the total dose over 6 hours, not per hour.