For a weight-based continuous infusion, the order is 5 mcg/kg/min. The patient weighs 70 kg. The drug concentration is 800 mg in 250 mL. What is the infusion rate in mL/hr?

For a weight-based continuous infusion, the order is 5 mcg/kg/min. The patient weighs 70 kg. The drug concentration is 800 mg in 250 mL. What is the infusion rate in mL/hr?

• A. 4.0 mL/hr
• B. 6.56 mL/hr
• C. 8.0 mL/hr
• D. 10.0 mL/hr

Answer: (B)

The key idea is to convert a weight-based dose into a flow rate by using the patient’s weight, then use the drug’s concentration to turn that dose into mL per hour. Start with the dose per minute: 5 mcg/kg/min times 70 kg equals 350 mcg/min, which is 0.350 mg/min. Convert to per hour: 0.350 mg/min × 60 min = 21 mg/hr. Next, use the concentration to find mL per hour: 800 mg in 250 mL means 3.2 mg per mL. To deliver 21 mg/hr, you need 21 mg/hr ÷ 3.2 mg/mL = 6.5625 mL/hr, which rounds to 6.56 mL/hr. Therefore, the infusion rate is 6.56 mL/hr.

The key idea is to convert a weight-based dose into a flow rate by using the patient’s weight, then use the drug’s concentration to turn that dose into mL per hour.

Start with the dose per minute: 5 mcg/kg/min times 70 kg equals 350 mcg/min, which is 0.350 mg/min. Convert to per hour: 0.350 mg/min × 60 min = 21 mg/hr.

Next, use the concentration to find mL per hour: 800 mg in 250 mL means 3.2 mg per mL. To deliver 21 mg/hr, you need 21 mg/hr ÷ 3.2 mg/mL = 6.5625 mL/hr, which rounds to 6.56 mL/hr.

Therefore, the infusion rate is 6.56 mL/hr.