Fentanyl: veterinary dose and monograph

At a glance

Drug class

Analgesic

Also known as

Sublimaze, Durogesic patch, Fentanyl citrate

Species with doses

Dogs, Cats, Horses and Reptiles

General dose range

0.002–0.005 mg/kg IV bolus then CRI — check the species tables for the indication

Routes

IV, Topical, Epidural

Last reviewed

1 October 2026

Indications

• Intra-operative and post-operative analgesia (bolus + CRI)
• Component of balanced/total intravenous anaesthesia
• Severe acute or cancer pain (ICU CRI or transdermal patch)
• Sedation/analgesia for painful procedures

Fentanyl dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

Dogs

• Analgesia loading bolus: Papich 5e: 3–5 µg/kg IV loading dose before a CRI; analgesic bolus 5–10 µg/kg q2h IV, IM or SC. Plumb’s p.515: 2–5 µg/kg IV then CRI (Wagner 2002); induction 1–5 µg/kg IV. Do not confuse µg/kg with mg/kg.
• Transdermal patch (background analgesia): Plumb’s p.515: patch absorption varies widely — dogs need 12–24 h to reach effect (cats 6–24 h), so apply before surgery or bridge with injectable opioids; release lasts about 3 days in dogs (5 in cats). Do not cut patches; avoid heating pads over the patch (toxicity); remove if febrile. Sites: thorax, inguinal area, metatarsus, tail base.
• Analgesia CRI: Papich 5e: 5 µg/kg/h after a 3–5 µg/kg load, increasing to 10 µg/kg/h if needed. Plumb’s p.515: 2–5 µg/kg/h for pain (Wagner 2002); 2–6 µg/kg/h (Hansen 2008). Monitor ventilation.
• Intra-operative CRI (MAC reduction): Papich 5e: 10 µg/kg IV then 5 µg/kg/h, increasing to 50 µg/kg/h if needed. Plumb’s p.515: 10–45 µg/kg/h for surgical analgesia/MAC reduction (Wagner; Mama); 10 µg/kg load + 10 µg/kg/h (Sano 2006). Ventilate — apnoea likely at the higher rates.
• Epidural analgesia: Plumb’s p.515 (Valverde 2008): 4 µg/kg diluted to 0.2 mL/kg with preservative-free saline or local anaesthetic; onset under 10 min, duration about 30 min.

Cats

• Analgesia / premedication bolus: Papich 5e: premedication 2–5 µg/kg IV; CRI loading dose 3–5 µg/kg IV. Watch for dysphoria and hyperthermia.
• Anaesthetic adjunct (bolus): Papich 5e: 0.02-0.04 mg/kg (20-40 mcg/kg) q2h IV, SQ or IM as an anaesthetic adjunct. Expect respiratory depression - ventilate and monitor.
• Analgesia CRI: Papich 5e: 2–5 µg/kg/h after a 3–5 µg/kg load, increasing up to 7 µg/kg/h if needed to control pain.

Horses

• Analgesia (transdermal patch): Plumb’s p.515: horses need 6 h or more to reach effect and patches release for about 2 days; apply on the neck or antebrachium. Absorption is variable. Narcotics can cause excitement and mask colic signs.

Reptiles

• Analgesia (transdermal / SC / CRI): Carpenter's 6th ed (Reptile analgesic table): transdermal 12 µg/h patch (ball pythons — reached mammalian therapeutic plasma levels in 4 h, applied over cranial epaxial muscles); 0.05 mg/kg SC (slider turtles, antinociceptive); 10 µg/kg/h IO CRI (bearded dragon, intra-op). Temperature markedly affects absorption. Mu-opioids give more reliable reptile analgesia than kappa-agonists.

Contraindications

Severe respiratory compromise without ventilatory support. Head trauma with raised intracranial pressure (relative). Use reduced doses in geriatric, debilitated or hypovolaemic patients. Patches: avoid heat sources (fever, heating pads, sun) — heat accelerates absorption and can cause fatal overdose. Known opioid hypersensitivity.

Species-specific warnings

Cats: Use lower doses; cats are prone to opioid dysphoria/excitation and to patch-associated hyperthermia. Titrate carefully.

Dogs: Discarded or chewed transdermal patches can rapidly kill a dog that ingests them — store and dispose securely.

Adverse effects

• Dose-dependent respiratory depression
• Bradycardia (vagally mediated — responsive to anticholinergics)
• Sedation, dysphoria/excitation (especially cats at high dose)
• Hypothermia, reduced GI motility/ileus
• Hyperthermia in cats with patches; panting in dogs

Drug interactions

• Other CNS depressants (sedatives, anaesthetics, other opioids): additive respiratory/CNS depression — reduce doses
• CYP3A4 inhibitors (ketoconazole, erythromycin): increased fentanyl levels
• Serotonergic drugs (SSRIs, tramadol, MAOIs): serotonin-syndrome risk
• Acepromazine/sedatives: enhance sedation and hypotension (often used deliberately in premed)

Pregnancy and lactation

Crosses the placenta — neonatal respiratory depression if used at parturition (have naloxone ready for neonates). Used peri-operatively when needed; titrate carefully.

Monitoring

• Respiratory rate, effort and SpO2/capnography during bolus and CRI
• Heart rate (bradycardia) and blood pressure
• Sedation/dysphoria score; temperature (hypothermia in dogs, hyperthermia in cats)
• Patch adhesion/placement and household safety (other pets, children)
• Controlled-drug accountability records

Toxicity and overdose

Overdose causes profound respiratory depression and apnoea, marked bradycardia, pinpoint pupils (dogs) and coma. Transdermal patches are a special hazard — heat, chewing/ingestion (especially by a second pet or child), or wrong size can be rapidly fatal. Very small absolute doses are dangerous given the potency.

Management: Antidote: naloxone 0.01–0.04 mg/kg IV/IM, repeated as needed (fentanyl may outlast a single naloxone dose — re-dose or use a naloxone CRI). Support ventilation/oxygenation (the priority), treat bradycardia with anticholinergics, IV fluids and warmth. Remove any patch immediately and decontaminate ingested patches.

Clinical pearls

• The go-to opioid for intra-op and ICU CRI analgesia — potent, titratable, cardiovascularly stable
• Always have naloxone and the ability to ventilate before using it
• Patches take 12–24 h to reach effect — start an injectable opioid to cover the gap, and never apply heat over the patch
• Bradycardia is vagal and usually responds to an anticholinergic; respiratory depression is the dangerous effect
• Account for every microgram — it is a controlled drug and lethal in tiny amounts to people/other pets

Mechanism of action

Pure agonist at mu-opioid receptors in the brain, spinal cord (dorsal horn) and periphery, inhibiting ascending nociceptive transmission and activating descending inhibitory pathways via G-protein coupling — reduced cAMP, decreased neuronal excitability and neurotransmitter release. High lipophilicity gives rapid CNS penetration and short action by redistribution.

Formulations and products

• Injection 50 mcg/mL (0.05 mg/mL)
• Transdermal patch 25 mcg/h
• Transdermal patch 50 mcg/h
• Transdermal patch 75 / 100 mcg/h
• Fentanyl injection (vet use) (Various (controlled)) — 50 mcg/mL, Injection
• Fentanyl citrate injection — 50 mcg/mL (2 mL / 10 mL ampoule), Injection (human-label)
• Durogesic / Fentapatch — 12.5 / 25 / 50 / 75 / 100 mcg/h patch, Transdermal patch (human-label)

Storage

Injection and patches: 15–30 °C, protect from light; SECURE controlled-drug storage with use logs. Dispose of used/unused patches safely (still contain drug — fatal if chewed/ingested).

Before you use this dose

Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

Other analgesics

• Buprenorphine
• Butorphanol
• Codeine
• Dipyrone (Metamizole)
• Gabapentin
• Hydromorphone
• Lidocaine HCl
• Methadone

Frequently asked questions