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Veterinary DrugCalculator

Veterinary CRI Calculator

A constant rate infusion (CRI) delivers a drug continuously at a steady dose. This calculator converts a CRI dose expressed in mcg/kg/min into a pump rate in mL/hr, using the concentration of the drug in the syringe or bag. It also shows how long a bag of a given size will last at that rate.

Formula

mg per minute  = (mcg/kg/min x body weight kg) / 1000
mL per minute  = mg per minute / concentration (mg/mL)
mL per hour    = mL per minute x 60

Worked example

A 10 kg patient at 5 mcg/kg/min with a 1 mg/mL concentration:

5 x 10 = 50 mcg/min
50 / 1000 = 0.05 mg/min
0.05 / 1 = 0.05 mL/min
0.05 x 60 = 3 mL/hr

When CRIs are used

CRIs are used when a drug needs to be delivered at a steady plasma level rather than as a bolus. Common situations include analgesia infusions, antiarrhythmic therapy, and prokinetic support. The choice of drug, dose and duration is a clinical decision and requires a verified reference and veterinary judgment.

What this calculator does not do

  • It does not verify the dose rate for a drug or a species.
  • It does not account for dilution steps or additives in the bag.
  • It does not decide whether a CRI is appropriate for a patient.