Drug Calculations
Helpful formulas:
mcg/kg/min
If a certain dose is ordered:
_______ mcg/kg/min X _______ kg ÷ ______ mcg/ML = ______ mL/h
Dosage
Pt weight
concentration
pump setting
If infusion pump is already set and running:
______ mcg/Ml X ______ mL/h ÷ 60 ÷ ______ kg = ______ mcg/kg/min
Concentration
pump setting
Pt weight
dosage
mcg/min
If a certain dose is ordered:
_______ mcg/min X 60 ÷ ______ mcg/mL = ______ mL/h
Dosage
concentration
pump setting
If infusion pump is already set and running:
______ mcg/mL X ______ mL/h ÷ 60 = ______ mcg/min
Concentration
pump setting
dosage
mg/min
If a certain dose is ordered:
_______ mg/min X 60 ÷ ______ mg/mL = ______ mL/h
Dosage
concentration
pump setting
If infusion pump is already set and running:
______ mg/mL X ______ mL/h ÷ 60 = ______ mg/min
Concentration
pump setting
dosage
mg/h
If a certain dose is ordered:
_______ mg/h ÷ ______ mg/mL = ______ mL/h
Dosage
concentration
pump setting
If infusion pump is already set and running:
______ mg/mL X ______ mL/h = ______ mg/h
Concentration
pump setting
dosage
Adapted from Giuliano, Richards & Kaye (1993) A New strategy for calculating medication infusion rates.
Critical Care Nurse. 13(6).
Calculating a Constant:
A Constant is the amount of drug delivered in units specified when the
infusion pump is set at 1cc/hr.
Basic Method for calculating a drug infusion CONSTANT
Step 1: Decide the “units” to be delivered in (e.g. mcg/kg/min).
Step 2: Using a calculator, enter the drug concentration in mg/cc
(e.g.100mg/250cc).
Step 3: If units you are to use involve microgram (mcg), multiply by 1000. If you
are delivering in milligrams, skip this step.
Step 4: If “per minute”, divide by 60. IF not per minute skip this step.
Step 5: If “per Kg”, divide by the patients weight in KG. If not skip this step.
The result of this calculation is the CONSTANT.
Formula: Mg/cc X 1000 60 Kg = Constant
Multiplying the pump rate by the constant will give you the dose infusing.
To determine what rate to set a pump to deliver a specified amount of drug: Divide the
amount desired by the constant.
Example # 1:
Dopamine runs at mcg/kg/min
Dopamine comes as 400mg/250cc
Patient’s weight is 75 kg
Pump infusing at 10cc/hr
Using formula
400 / 250 = 1.6
1.6 X 1000 = 1600
1600 / 60 = 26.66666
26.66666 / 75 = 0.3555 (this is your constant)
0.3555 X 10 = 3.6 mcg/kg/min (dose infusing)
Example # 2:
Levophed runs at Mcg/min
Levophed is mixed at 4mg/250ml
Pump is infusing at 7cc/hr
Using formula
4/250 = 0.016
0.016X 1000 = 16
16 / 60 = 0.2666 (this is your constant)
0.2666 X 7 = 1.86 mcg/min