Converting mcg/min to ml/hr for IV Infusions

Calculating mcg/min infusions is used when a medication is prescribed as a fixed rate per minute rather than being based on body weight. This is common for some intravenous infusions where the dose is titrated according to patient response. The calculation converts the prescribed dose into mL/hr so it can be set on an infusion pump.

What You Need to Know

mcg/min calculations involve converting a fixed dose per minute into an hourly infusion rate. Unlike weight-based calculations, the patient’s weight is not used.

Key points:

• the prescribed dose is already given as mcg per minute

• no weight calculation is required

• the final answer must be in mL/hr

• the calculation involves converting minutes to hours

A quick check:

• higher mcg/min = higher mL/hr

• larger stock strength = lower mL/hr

• final answer should be appropriate for an infusion pump

The Formula

mL/hr = (mcg/min × 60) ÷ concentration in mcg/mL

Where:
mcg/min = prescribed dose in micrograms per minute
60 = conversion from minutes to hours
concentration = amount of drug in the solution (mcg/mL)

Alternative form:
mL/hr = (mcg/min × 60 × total volume in mL) ÷ total drug amount in mcg

Worked Examples

Example 1
Order: 10 mcg/min
Stock: 200 mg in 50 mL

Convert stock:
200 mg = 200000 mcg

mL/hr = (10 × 60 ÷ 200000) × 50
= (600 ÷ 200000) × 50
= 0.003 × 50
= 0.15

Answer: 0.15 mL/hr

Example 2
Order: 25 mcg/min
Stock: 100 mg in 50 mL

100 mg = 100000 mcg

mL/hr = (25 × 60 ÷ 100000) × 50
= (1500 ÷ 100000) × 50
= 0.015 × 50
= 0.75

Answer: 0.75 mL/hr

Example 3
Order: 5 mcg/min
Stock: 50 mg in 50 mL

50 mg = 50000 mcg

mL/hr = (5 × 60 ÷ 50000) × 50
= (300 ÷ 50000) × 50
= 0.006 × 50
= 0.3

Answer: 0.3 mL/hr

Practice Questions

1. Order: 15 mcg/min, stock: 200 mg in 50 mL

2. Order: 30 mcg/min, stock: 150 mg in 50 mL

3. Order: 8 mcg/min, stock: 80 mg in 40 mL

4. Order: 20 mcg/min, stock: 100 mg in 50 mL

5. Order: 12 mcg/min, stock: 120 mg in 60 mL

   (Scroll down for answers)

Answers

1. 15 × 60 = 900, 200 mg = 200000 mcg
   (900 ÷ 200000) × 50 = 0.225 mL/hr

2. 30 × 60 = 1800, 150 mg = 150000 mcg
   (1800 ÷ 150000) × 50 = 0.6 mL/hr

3. 8 × 60 = 480, 80 mg = 80000 mcg
   (480 ÷ 80000) × 40 = 0.24 mL/hr

4. 20 × 60 = 1200, 100 mg = 100000 mcg
   (1200 ÷ 100000) × 50 = 0.6 mL/hr

5. 12 × 60 = 720, 120 mg = 120000 mcg
   (720 ÷ 120000) × 60 = 0.36 mL/hr