Fentanyl CRI
Short-acting opioid CRI for moderate-to-severe acute pain in dogs and cats. Used for postoperative and perioperative analgesia, pancreatitis, peritonitis, neoplastic pain, and other inpatient analgesia where a continuous opioid infusion is appropriate. The short duration suits critical illness. The infusion can be paused for neurologic reassessment and resumed without a long washout.
How this calculator works
Enter the patient's weight and dose. The calculator returns the pump rate to deliver that dose at the chosen bag concentration. The default 5 µg/mL preparation suits most dogs and cats; alternatives are available under Use a different concentration.
After you compute, the result panel shows a loading dose alongside the CRI rate. The matched value is the IV bolus that brings plasma to steady-state for your chosen CRI rate (1:1 µg/kg per µg/kg/hr), the specialist convention for short-half-life drugs.
Two scenarios appear: perioperative analgesia (matched value applies) and emergent severe pain (titrated, 10–50 µg/kg). Fentanyl is a potent respiratory depressant. Monitor respiratory rate closely and keep naloxone immediately available.
Enter a patient weight to see the result.
How the calculation works
Fentanyl CRI is dosed in µg/kg/hr. The CRI rate calculation is:
Patient weight (kg) times dose (µg per kg per hour) gives total µg per hour. Dividing by concentration (µg per mL) yields mL per hour. No unit-time conversion needed because dose and rate are both per-hour.
Worked example with current inputs
Enter a patient weight to see the worked example.
Recommended dilutions
| Target concentration | Dilution | When useful |
|---|---|---|
| 5 µg/mL | Remove 5 mL from a 50 mL bag of 0.9% NaCl, then add 5 mL of 50 µg/mL stock (250 µg in 50 mL final = 5 µg/mL) | Standard for most patients on an IV pump |
| 10 µg/mL | Remove 10 mL from a 50 mL bag of 0.9% NaCl, then add 10 mL of 50 µg/mL stock (500 µg in 50 mL final = 10 µg/mL) | Larger patients or higher-dose work where carrier-fluid load matters |
| 1 µg/mL | Remove 5 mL from a 250 mL bag of 0.9% NaCl, then add 5 mL of 50 µg/mL stock (250 µg in 250 mL final = 1 µg/mL) | Small patients on a syringe pump or low-rate IV pump |
Fentanyl is conventionally prepared as a diluted bag for IV-pump CRI, not run from the 50 µg/mL stock vial directly. Use the recipe matched to the patient's size; the default 5 µg/mL covers most dogs and cats and produces pump rates in the reliable 3–80 mL/hr range across typical doses. Compatible carrier fluids include 0.9% NaCl, LRS, Plasma-Lyte, and 5% dextrose; 6% hetastarch is also compatible if a colloid line is already running. Direct-from-stock administration (50 µg/mL via syringe pump) is reserved for very small patients where minimizing carrier fluid is essential and the pump can deliver fractional mL/hr reliably. Once a vial is punctured, draw what is needed for the current patient and discard the remainder; fentanyl is a DEA Schedule II controlled substance and federal / state disposal rules apply. Document waste.
Dilution helper — Fentanyl CRI
Work out how many mL of stock drug and diluent to combine for any target concentration. Stock is pre-filled for Fentanyl CRI; change it if you're using a different vial.
Enter stock, target concentration, and final volume.