Worked example

Weight-based IV infusion — practice problem 7

A patient weighing 75 kg has dopamine 800 mg in 500 mL. The prescriber orders 7.5 mcg/kg/min.

Weight75 kg

Ordered rate7.5 mcg/kg/min

Bag800 mg in 500 mL

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

Answer: 21.1 mL/hr

Step-by-step solution

1. Find the bag concentration in mcg/mL

800 mg × ( 1000 mcg ÷ 1 mg ) ÷ 500 mL

= 1600 mcg/mL

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

7.5 mcg/kg/min × 75 kg

= 562.5 mcg/min

3. Convert to mcg per hour

562.5 mcg/min × ( 60 min ÷ 1 hr )

= 33750 mcg/hr

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

33750 mcg/hr × ( 1 mL ÷ 1600 mcg )

= 21.1 mL/hr