The drug concentration is 2 mg/mL. To deliver 0.4 mg/min, what is the infusion rate in mL per minute?

• A. 0.4 mL/min
• B. 0.04 mL/min
• C. 0.2 mL/min
• D. 2.0 mL/min

Answer: (C)

To figure the infusion rate, use this relationship: infusion rate (mL per minute) = dose rate (mg per minute) ÷ concentration (mg per mL). Here you need 0.4 mg each minute and the solution has 2 mg in every mL, so 0.4 ÷ 2 = 0.2 mL per minute. A quick check: 0.2 mL/min × 2 mg/mL = 0.4 mg/min, which matches the desired dose. If you used a different rate, you’d deliver a different amount per minute—for example, 0.4 mL/min would give 0.8 mg/min, 0.04 mL/min would give 0.08 mg/min, and 2.0 mL/min would give 4 mg/min.