Worked example

Weight-based IV infusion — practice problem 5

A patient weighing 65 kg has nitroglycerin 50 mg in 250 mL. The prescriber orders 7.5 mcg/kg/min.

Weight65 kg

Ordered rate7.5 mcg/kg/min

Bag50 mg in 250 mL

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

Answer: 146.3 mL/hr

Step-by-step solution

1. Find the bag concentration in mcg/mL

50 mg × ( 1000 mcg ÷ 1 mg ) ÷ 250 mL

= 200 mcg/mL

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

7.5 mcg/kg/min × 65 kg

= 487.5 mcg/min

3. Convert to mcg per hour

487.5 mcg/min × ( 60 min ÷ 1 hr )

= 29250 mcg/hr

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

29250 mcg/hr × ( 1 mL ÷ 200 mcg )

= 146.3 mL/hr