Lessons · Weight-based IV infusion
Dosage calculation
Weight-based IV infusion (mcg/kg/min to mL/hr) Critical-care drips like dopamine are ordered in mcg/kg/min but pumps are set in mL/hr. This is the full dimensional-analysis problem: find the bag concentration in mcg/mL, multiply the rate by weight, convert minutes to hours, and divide by concentration so every unit cancels except mL/hr.
The formula mL/hr = (ordered mcg/kg/min × weight kg × 60) ÷ concentration (mcg/mL)
How to solve it Convert the bag to mcg/mL: drug mg × 1000 ÷ bag mL. Multiply the ordered mcg/kg/min by the patient's weight in kg → mcg/min. Multiply by 60 min/hr → mcg/hr. Divide by the concentration (mcg/mL) so mcg cancels, leaving mL/hr. Common mistakes Forgetting the mg→mcg step when finding concentration. Leaving the rate in mcg/min instead of converting to per hour. Cancelling units carelessly - write every unit and confirm only mL/hr remains. Safety check: High-alert infusions demand an independent double-check of the pump rate. Show every unit so nothing is left uncancelled.
Worked examples
See it solved A patient weighing 65 kg has esmolol 2500 mg in 250 mL. The prescriber orders 50 mcg/kg/min.
Weight 65 kg
Ordered rate 50 mcg/kg/min
Bag 2500 mg in 250 mL
What pump rate (mL/hr) delivers this order?
Answer: 19.5 mL/hr
Step-by-step solution 1. Find the bag concentration in mcg/mL
2500 mg × ( 1000 mcg ÷ 1 mg ) ÷ 250 mL
= 10000 mcg/mL
2. Dose per minute: multiply the rate by the patient's weight
50 mcg/kg/min × 65 kg
= 3250 mcg/min
3. Convert to mcg per hour
3250 mcg/min × ( 60 min ÷ 1 hr )
= 195000 mcg/hr
4. Divide by concentration so mcg cancels, leaving mL/hr
195000 mcg/hr × ( 1 mL ÷ 10000 mcg )
= 19.5 mL/hr
A patient weighing 60 kg has esmolol 2500 mg in 250 mL. The prescriber orders 100 mcg/kg/min.
Weight 60 kg
Ordered rate 100 mcg/kg/min
Bag 2500 mg in 250 mL
What pump rate (mL/hr) delivers this order?
Answer: 36 mL/hr
Step-by-step solution 1. Find the bag concentration in mcg/mL
2500 mg × ( 1000 mcg ÷ 1 mg ) ÷ 250 mL
= 10000 mcg/mL
2. Dose per minute: multiply the rate by the patient's weight
100 mcg/kg/min × 60 kg
= 6000 mcg/min
3. Convert to mcg per hour
6000 mcg/min × ( 60 min ÷ 1 hr )
= 360000 mcg/hr
4. Divide by concentration so mcg cancels, leaving mL/hr
360000 mcg/hr × ( 1 mL ÷ 10000 mcg )
= 36 mL/hr
A patient weighing 75 kg has milrinone 20 mg in 100 mL. The prescriber orders 0.5 mcg/kg/min.
Weight 75 kg
Ordered rate 0.5 mcg/kg/min
Bag 20 mg in 100 mL
What pump rate (mL/hr) delivers this order?
Answer: 11.3 mL/hr
Step-by-step solution 1. Find the bag concentration in mcg/mL
20 mg × ( 1000 mcg ÷ 1 mg ) ÷ 100 mL
= 200 mcg/mL
2. Dose per minute: multiply the rate by the patient's weight
0.5 mcg/kg/min × 75 kg
= 37.5 mcg/min
3. Convert to mcg per hour
37.5 mcg/min × ( 60 min ÷ 1 hr )
= 2250 mcg/hr
4. Divide by concentration so mcg cancels, leaving mL/hr
2250 mcg/hr × ( 1 mL ÷ 200 mcg )
= 11.3 mL/hr
Safe number notation Every number on DoseDrill is written the safe way - and here is why it matters:
Always use a leading zero for amounts under 1: write 0.5 mg , never .5 mg . A missing zero is read as 5 - a ten-fold overdose.Never use a trailing zero after a decimal: write 5 mg , never 5.0 mg . A stray zero is read as 50 .Read the full safe-notation guide →
Keep going More worked weight-based iv infusion examples:
Related formulas:
Practice only - never for real medication. DoseDrill generates problems to help nursing students learn dosage calculation. It must never be used to calculate, prepare, or administer medication to an actual patient. Real administration requires an independent double-check, current drug references, and your facility's policy. A wrong dose can harm or kill - always verify with a licensed professional.