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Fentanyl

Prescription
Synthetic opioid analgesic — full mu-agonist
Last reviewed 19 Apr 2026 · PetCare.AI Editorial Team
Species
Dog, Cat
Brands
4 available
Interactions
10 documented
Formulations
6

Mechanism of action

Potent full agonist at mu-opioid receptors (80-100x morphine potency); provides rapid-onset, short-duration analgesia; ideal for CRI and perioperative pain management

At a glance

Class
Synthetic opioid analgesic — full mu-agonist
Schedule
Prescription
Storage
Store below 25°C, protect from light. CONTROLLED SUBSTANCE (Schedule H1/Narcotic). Maintain strict controlled substance log. Patches: fold used patches adhesive-to-adhesive and dispose properly.

Dosing

🐕

Dog

Perioperative analgesia (IV bolus)
Dose
2–5 mcg/kg
Route
IV (slow)
Frequency
Every 20-30 minutes or CRI
Max dose
200 mcg/dose; 2000 mcg/day
Duration: Short duration (20-30 min IV); transition to CRI for sustained analgesia
Intra-operative CRI
Dose
2–10 mcg/kg/hr
Route
IV CRI
Frequency
Continuous infusion (after loading bolus)
Max dose
10 mcg/kg/hr/dose; 240 mcg/kg/hr/day
Duration: Duration of surgery + 4-6h post-op; taper before discontinuation
Post-operative CRI (severe pain)
Dose
1–6 mcg/kg/hr
Route
IV CRI
Frequency
Continuous infusion
Max dose
6 mcg/kg/hr/dose; 144 mcg/kg/hr/day
Duration: 24-72 hours post-op; taper over 12-24h before stopping
Transdermal patch
Dose
2–5 mcg/kg/hr
Route
Transdermal
Frequency
Every 72 hours
Max dose
100 mcg/hr
Duration: Replace every 72 hours; onset 12-24h
🐈

Cat

Perioperative analgesia (IV bolus)
Dose
1–3 mcg/kg
Route
IV (slow)
Frequency
Every 20-30 minutes or CRI
Max dose
20 mcg/dose; 200 mcg/day
Duration: Short duration; CRI preferred
CRI analgesia
Dose
1–5 mcg/kg/hr
Route
IV CRI
Frequency
Continuous infusion
Max dose
5 mcg/kg/hr/dose; 120 mcg/kg/hr/day
Duration: 24-48 hours; taper before stopping
Transdermal patch
Dose
12.5–25 mcg/hr patch
Route
Transdermal
Frequency
Every 72-96 hours (variable absorption in cats)
Max dose
25 mcg/hr
Duration: Replace every 72-96h; onset 6-12h in cats
Educational reference only
This information is provided for educational purposes and is not a substitute for professional veterinary advice, diagnosis, or treatment. Always consult a qualified veterinarian before administering any medication to your pet. Find a vet near you →

Formulations

💉

Injectable — 1

Strength
50mcg/mL
Available in India
💊

Transdermal patch — 5

Strength
12.5mcg/hr
Available in India
Strength
25mcg/hr
Available in India
Strength
50mcg/hr
Available in India
Strength
75mcg/hr
Available in India
Strength
100mcg/hr
Available in India

Storage

Store below 25°C, protect from light. CONTROLLED SUBSTANCE (Schedule H1/Narcotic). Maintain strict controlled substance log. Patches: fold used patches adhesive-to-adhesive and dispose properly.

Safety

Absolute contraindications — do not use

  • Concurrent MAOIs
    Severe opioid toxicity — serotonin syndrome-like reaction
    Selegiline
  • Untreated hypothyroidism
    Reduced metabolism of opioids — risk of prolonged/severe effects

Use with caution

  • Head trauma / raised ICP
    Respiratory depression increases PaCO2, which increases ICP
  • Bradycardia
    Fentanyl causes vagal-mediated bradycardia — pre-treat with anticholinergic if needed
  • Hepatic impairment
    Primarily hepatically metabolised — reduced clearance

Adverse effects

Common
Bradycardia
Respiratory depression
Panting (thermal dysregulation — dogs)
Nausea
Sedation
Serious
Respiratory arrest
Severe bradycardia
Chest wall rigidity (rapid IV bolus)
Hypotension
Ileus

Monitoring parameters

Respiratory rate (must be >8/min)SpO2Heart rateBlood pressurePain scoreSedation levelTemperatureGI motility
Educational reference only
This information is provided for educational purposes and is not a substitute for professional veterinary advice, diagnosis, or treatment. Always consult a qualified veterinarian before administering any medication to your pet. Find a vet near you →

Interactions

Major — 4

Tramadol
major
Dual opioid agonism: risk of serotonin syndrome and severe respiratory depression
Management: Avoid concurrent use. Discontinue tramadol before starting fentanyl CRI.
Butorphanol
major
Butorphanol is a mu-antagonist/kappa-agonist that can partially reverse fentanyl's mu-agonist effects
Management: Avoid concurrent use. Butorphanol can reduce fentanyl analgesia. Use one or the other.
Buprenorphine
major
Buprenorphine displaces fentanyl from mu-receptors due to higher binding affinity, reducing fentanyl analgesic effect.
Management: Do not combine. If fentanyl CRI running and analgesia inadequate, increase fentanyl dose rather than adding buprenorphine.
Naltrexone
major
Naltrexone blocks all opioid receptor activity, rendering fentanyl ineffective.
Management: Discontinue naltrexone 72h before surgery. If emergency arises, non-opioid analgesia (NSAID, ketamine, local anesthetic) required.

Moderate — 5

Diazepam
moderate
Opioid + benzodiazepine: additive respiratory depression and CNS depression
Management: Standard combination for neuroleptanalgesia. Monitor respiratory rate and SpO2 closely.
Propofol
moderate
Fentanyl premedication reduces propofol induction dose by 30-50%. Additive respiratory depression and apnea risk.
Management: Standard technique: reduce propofol dose when fentanyl premedicated. Titrate to effect. Have intubation and IPPV equipment ready.
Isoflurane
moderate
Fentanyl CRI reduces isoflurane MAC by 40-60% (MAC-sparing effect), allowing lower vaporizer settings and less cardiovascular depression from inhalant.
Management: Intended beneficial interaction. Reduce vaporizer setting and monitor depth. Standard balanced anesthesia technique.
Pregabalin
moderate
Additive CNS depression. Pregabalin augments opioid analgesia but increases sedation and respiratory depression risk.
Management: Reduce opioid dose. Monitor respiratory function. Useful for neuropathic pain.
Sevoflurane
moderate
Fentanyl CRI reduces sevoflurane MAC by 40-60%, allowing lower vaporizer settings.
Management: Intended beneficial interaction (balanced anesthesia). Reduce vaporizer setting and monitor depth.

Minor — 1

Naloxone
minor
Naloxone is a mu-opioid antagonist — reverses fentanyl effects (intentional use for overdose reversal)
Management: This is the intended use. Give naloxone IV to reverse fentanyl respiratory depression. Effect is shorter than fentanyl — may need repeat doses.
Educational reference only
This information is provided for educational purposes and is not a substitute for professional veterinary advice, diagnosis, or treatment. Always consult a qualified veterinarian before administering any medication to your pet. Find a vet near you →

Brands

International

Fentanyl Citrate
Various (hospital)
Durogesic (patch)
Janssen

India

Trofentyl
Troikaa
Fentanyl
Neon Labs

FAQs

Frequently asked questions

›What is Fentanyl?
Fentanyl is a synthetic opioid analgesic — full mu-agonist used in pets. Potent full agonist at mu-opioid receptors (80-100x morphine potency); provides rapid-onset, short-duration analgesia; ideal for CRI and perioperative pain management
›What is Fentanyl used for in pets?
Fentanyl is used in veterinary medicine for: Perioperative analgesia (IV bolus); Intra-operative CRI; Post-operative CRI (severe pain); Transdermal patch; CRI analgesia.
›What is the Fentanyl dose for dogs?
For dogs, Fentanyl is typically dosed as follows — Perioperative analgesia (IV bolus): 2–5 mcg/kg IV (slow) Every 20-30 minutes or CRI; Intra-operative CRI: 2–10 mcg/kg/hr IV CRI Continuous infusion (after loading bolus); Post-operative CRI (severe pain): 1–6 mcg/kg/hr IV CRI Continuous infusion. Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.
›What is the Fentanyl dose for cats?
For cats, Fentanyl is typically dosed as follows — Perioperative analgesia (IV bolus): 1–3 mcg/kg IV (slow) Every 20-30 minutes or CRI; CRI analgesia: 1–5 mcg/kg/hr IV CRI Continuous infusion; Transdermal patch: 12.5–25 mcg/hr patch Transdermal Every 72-96 hours (variable absorption in cats). Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.
›What are the side effects of Fentanyl?
Common: Bradycardia, Respiratory depression, Panting (thermal dysregulation — dogs), Nausea, Sedation. Serious (call your vet immediately): Respiratory arrest, Severe bradycardia, Chest wall rigidity (rapid IV bolus), Hypotension, Ileus.
›Does Fentanyl need a prescription?
Yes. Fentanyl is a prescription medication and should only be administered under veterinary supervision.
›When should Fentanyl not be used?
Do not use Fentanyl if: Concurrent MAOIs; Untreated hypothyroidism.
Educational reference only
This information is provided for educational purposes and is not a substitute for professional veterinary advice, diagnosis, or treatment. Always consult a qualified veterinarian before administering any medication to your pet. Find a vet near you →

References

References

The PetCare.AI drug reference is built from 13 authoritative sources cited across 580 drug monographs.

Textbooks & handbooks — 5

  • Plumb's Veterinary Drug Handbook
  • Withrow & MacEwen's Small Animal Clinical Oncology
  • Merck Veterinary Manual
  • NRC Nutrient Requirements of Dogs and Cats
  • Veterinary Pharmacology and Therapeutics (Riviere & Papich)

Clinical guidelines & consensus — 4

  • ASPCA Animal Poison Control Center Guidelines
  • AAHA Diabetes Management Guidelines
  • ASPCA Poison Control Guidelines
  • RECOVER CPR Guidelines

Journals & peer-reviewed studies — 2

  • EPIC Study (J Vet Intern Med 2016)
  • JVIM FAT CAT Study

Regulatory & approvals — 1

  • CDSCO Veterinary Drug Approval Registry (1969–2026)

Databases — 1

  • Washington State University VCPL MDR1 Database
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