Worked example

Weight-based IV infusion — practice problem 2

A patient weighing 90 kg has dobutamine 500 mg in 250 mL. The prescriber orders 2 mcg/kg/min.

Weight90 kg

Ordered rate2 mcg/kg/min

Bag500 mg in 250 mL

What pump rate (mL/hr) delivers this order?

Answer: 5.4 mL/hr

Step-by-step solution

1. Find the bag concentration in mcg/mL

500 mg × ( 1000 mcg ÷ 1 mg ) ÷ 250 mL

= 2000 mcg/mL

2. Dose per minute: multiply the rate by the patient's weight

2 mcg/kg/min × 90 kg

= 180 mcg/min

3. Convert to mcg per hour

180 mcg/min × ( 60 min ÷ 1 hr )

= 10800 mcg/hr

4. Divide by concentration so mcg cancels, leaving mL/hr

10800 mcg/hr × ( 1 mL ÷ 2000 mcg )

= 5.4 mL/hr