Fentanyl
Fentanyl citrate
Also known as: Sublimaze Β· Duragesic Β· Actiq Β· Fentora Β· Ionsys Β· Fentadon Β· Durogesic Β· Fentanyl citrate Β· fentanylum Β· fentanyli citras Β· phentanyl citrate Β· McN-JR-4263-49 Β· Fentanil
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
π NA β North Americaπ EU β Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Perioperative pain | The combination of a 10 micro-grams/kg loading dose IV followed by a CRI of 10 micrograms/kg/hour | IV/CRI | Continuous | Perioperative | π NA |
| Pain management | 2-5 micrograms/kg IV, followed by a CRI at 2-5 micrograms/kg/hr | IV/CRI | Continuous | β | π NA |
| Surgical analgesia | CRI at 10-45 micrograms/kg/hr | CRI | Continuous | Intraoperative | π NA |
| Analgesia | 2-6 micrograms/kg/hour | CRI | Continuous | β | π NA |
| Induction | 0.001-0.005 mg/kg IV | IV | Single dose | β | π NA |
| MAC reduction during general anesthesia | 10-45 micrograms/kg/hr CRI | CRI | Continuous | Intraoperative | π NA |
| Severe to excruciating pain in the emergent patient | Fentanyl at 1050 micrograms/kg, administered IV titrated to effect; use the effective dose as an hourly CRI. | IV/CRI | Titrated to effect | β | π NA |
| Epidural for pain control | 0.004 mg/kg (4 micrograms/kg), diluted with 0.2 mL with preservative-free saline or local anesthetic. | Epidural | Single dose | 1/2 hour | π NA |
| Transdermal Analgesia (<5kg) | 25 mcg/hr or 12.5 mcg/hr | Transdermal | q72h | β | π NA |
| Transdermal Analgesia (5-10 kg) | 25 mcg/hr | Transdermal | q72h | β | π NA |
| Transdermal Analgesia (10-20 kg) | 50 mcg/hr | Transdermal | q72h | β | π NA |
| Transdermal Analgesia (20-30 kg) | 75 mcg/hr | Transdermal | q72h | β | π NA |
| Transdermal Analgesia (>30 kg) | 100 mcg/hr | Transdermal | q72h | β | π NA |
| Intraoperative analgesia | Intermittent bolus doses or continuous rate infusion (exact dose not specified) | IV | Intermittent or CRI | Intraoperative | π EU |
| Postoperative analgesia | Low end of the dose range by continuous rate infusion | IV | CRI | Postoperative | π EU |
| Postoperative or chronic pain | Transdermal patch (size based on patient requirement) | Topical | Apply 24 hours before surgery | Up to 72 hours | π EU |
- Perioperative pain: Guideline for CRI during general anesthesia
- Pain management: Loading dose followed by CRI
- Severe to excruciating pain in the emergent patient: Note: '1050' appears exactly as written in source text, likely a typo for 10-50. May combine with ketamine and lidocaine.
- Epidural for pain control: Onset in less than 10 minutes
- Transdermal Analgesia (<5kg): Apply 12-24 hours prior to need. Half-patch dosing may be desired for very small dogs.
- Transdermal Analgesia (5-10 kg): Apply 12-24 hours prior to need.
- Transdermal Analgesia (10-20 kg): Apply 12-24 hours prior to need.
- Transdermal Analgesia (20-30 kg): Apply 12-24 hours prior to need.
- Transdermal Analgesia (>30 kg): Apply 12-24 hours prior to need.
- Intraoperative analgesia: Give slowly to avoid severe bradycardia/asystole.
- Postoperative analgesia: Monitor respiratory function closely.
- Postoperative or chronic pain: Takes ~24 hours to attain adequate plasma concentrations. Use as an adjunctive analgesic.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Perioperative pain | 2-3 micrograms/kg IV plus 2-3 micrograms/kg/hour IV infusion | IV/CRI | Continuous | Perioperative | π NA |
| Pain management | 1-3 micrograms/kg IV, followed by a CRI at 1-4 micrograms/kg/hr | IV/CRI | Continuous | β | π NA |
| Surgical analgesia | CRI at 10-30 micrograms/kg/hr | CRI | Continuous | Intraoperative | π NA |
| Analgesia | 2-4 micrograms/kg/hour | CRI | Continuous | β | π NA |
| Induction | 0.001-0.002 mg/kg IV | IV | Single dose | β | π NA |
| MAC reduction during general anesthesia | 10-20 micrograms/kg/hr CRI | CRI | Continuous | Intraoperative | π NA |
| Severe to excruciating pain in the emergent patient | Fentanyl at 1050 micrograms/kg, administered IV titrated to effect; use the effective dose as an hourly CRI. | IV/CRI | Titrated to effect | β | π NA |
| Epidural for pain control | 0.004 mg/kg (4 micrograms/kg), diluted 0.2 mL with preservative-free saline or local anesthetic. | Epidural | Single dose | 1/2 hour | π NA |
| Maintenance analgesia/heavy sedation in critically ill hypotensive animals | fentanyl at 0.5-0.8 micrograms/kg/minute (equivalent to 30-50 micrograms/kg/hr). | CRI | Continuous | β | π NA |
| Transdermal Analgesia | 25 mcg/hr or 12.5 mcg/hr | Transdermal | q120h | Up to 5 days | π NA |
| Intraoperative analgesia | Intermittent bolus doses or continuous rate infusion (exact dose not specified) | IV | Intermittent or CRI | Intraoperative | π EU |
| Postoperative analgesia | Low end of the dose range by continuous rate infusion | IV | CRI | Postoperative | π EU |
| Postoperative or chronic pain | Transdermal patch (size based on patient requirement) | Topical | Apply 7 hours before surgery | Up to 72 hours | π EU |
- Pain management: Loading dose followed by CRI
- Severe to excruciating pain in the emergent patient: Note: '1050' appears exactly as written in source text, likely a typo for 10-50.
- Epidural for pain control: Onset in less than 10 minutes
- Maintenance analgesia/heavy sedation in critically ill hypotensive animals: Used in addition to a local line block. May combine with midazolam.
- Transdermal Analgesia: Apply 6-24 hours prior to need. 12 mg patches are available for very small cats.
- Intraoperative analgesia: Give slowly to avoid severe bradycardia/asystole.
- Postoperative analgesia: Monitor respiratory function closely.
- Postoperative or chronic pain: Takes ~7 hours to attain adequate plasma concentrations. Use as an adjunctive analgesic.
Small Mammals
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Perioperative pain (Rabbits/Rodents/Small Mammals) | 5-20 micrograms/kg IV bolus | IV | Single dose | 30-60 minute duration | π NA |
| Postoperative analgesia (Rabbits) | 1/2 small patch (25 micrograms/hr) per medium sized rabbit (3 kg) every 3 days. Do not cut patch | Transdermal | q72h | β | π NA |
- Perioperative pain (Rabbits/Rodents/Small Mammals): Causes sedation and respiratory depression
Ferrets
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Pre-op dose | 5-10 micrograms/kg IV | IV | Single dose | Pre-op | π NA |
| Intra-operatively | CRI at 10-20 micrograms/kg/hr with a ketamine CRI (0.3-0.4 mg/kg/hr) | CRI | Continuous | Intraoperative | π NA |
| Postoperatively | 2-5 micrograms/kg/hr with a ketamine CRI. | CRI | Continuous | Postoperative | π NA |
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Transdermal Analgesia (350-500 kg) | 100 mcg/hr | Transdermal | q48h | β | π NA |
- Transdermal Analgesia (350-500 kg): Apply 6+ hours prior to need. ARCI UCGFS Class 1 Drug.
Swine
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Transdermal Analgesia (17-25 kg) | 50 mcg/hr | Transdermal | β | β | π NA |
Sheep
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Transdermal Analgesia | 25 mcg/hr | Transdermal | β | β | π NA |
Goats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Transdermal Analgesia | 25 mcg/hr | Transdermal | β | β | π NA |
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Fentanyl is a highly potent, synthetic phenylpiperidine-derivative Class-II opiate analgesic used extensively in veterinary medicine for the management of moderate to severe pain.
βKey Pharmacological Features:β
- βPotency:β Approximately 75 to 100 times more potent than morphine.
- βLipophilicity:β Fentanyl is highly lipophilic, which allows it to rapidly cross the blood-brain barrier (resulting in a very fast onset of action when given IV) and makes it an excellent candidate for transdermal delivery.
- βDuration:β When administered as a single IV bolus, its duration of effect is extremely short (15-30 minutes) due to rapid redistribution from the brain to other tissues. Therefore, it is most commonly administered via βConstant Rate Infusion (CRI)β or transdermal patch for sustained analgesia.
βClinical Applications:β
- Adjunctive control of postoperative pain.
- Management of severe, chronic, dull, or non-specific widespread pain (e.g., cancer, pancreatitis, aortic thromboembolism).
- Perioperative use to significantly reduce the Minimum Alveolar Concentration (MAC) of inhalant anesthetics, providing cardiovascular stability in compromised patients.
βClinical Pearl:β While transdermal patches are highly convenient, absorption is notoriously variable among individual animals. A "rescue" injectable analgesic should always be available when relying on transdermal fentanyl.
Mechanism of action
Fentanyl is a highly selective βfull agonist at the mu-opioid receptor (MOR)β.
βMechanism Pathway:β
- βReceptor Binding:β Fentanyl binds to presynaptic and postsynaptic mu-receptors primarily located in the central nervous system (limbic system, spinal cord, thalamus, midbrain) and peripheral tissues.
- βG-Protein Activation:β Binding activates inhibitory G-proteins (Gi/Go).
- βCellular Effects:β
- Inhibits adenylate cyclase, decreasing intracellular cAMP.
- Promotes the opening of inward-rectifying potassium (K+) channels, leading to neuronal hyperpolarization.
- Inhibits the opening of voltage-gated calcium (Ca2+) channels on presynaptic nerve terminals.
- βAnalgesia:β This cascade profoundly inhibits the release of excitatory, nociceptive neurotransmitters (such as Substance P and glutamate) and decreases the excitability of postsynaptic neurons, effectively blocking pain transmission.
Safety & warnings
Contraindications
- Known hypersensitivity to fentanyl or patch adhesive
- Conditions where additional respiratory or CNS depression would be deleterious
- No specific contraindications available in the monograph (use with caution in patients with respiratory compromise)
Adverse effects
- Dose-related respiratory depression
- CNS depression (sedation)
- Circulatory depression (bradycardia)
- Dysphoria or agitation (especially in cats)
- Urine retention
- Constipation
- Contact dermatitis/rash at patch site
- Altered thermoregulation (hypothermia or hyperthermia)
- Severe bradycardia
- Asystole (with rapid IV injection)
- Reduction in heart rate
Precautions
βPatient Selection:β Use with extreme caution in geriatric, severely ill, or debilitated patients, and those with preexisting respiratory compromise.
βTransdermal Patch Warnings:β
- βHeat Exposure:β Do NOT allow the applied patch to be exposed to exogenous heat sources (e.g., heating pads, heated cages, direct sunlight). Heat significantly increases drug release and absorption, which has resulted in fatal overdoses.
- βFever:β Febrile patients may have increased absorption of fentanyl and require intense monitoring. Consider removing the patch if a fever develops.
- βPatch Integrity:β Do NOT cut patches unless specifically advised by a pharmacist (cutting alters the drug-releasing membrane of gel-reservoir patches, leading to rapid, uncontrolled drug release).
- βVariable Absorption:β Absorption is highly variable. Always have injectable rescue analgesia available.
βFeline Specifics:β Opioids may cause mydriasis (dilated pupils) in cats. Approach slowly to avoid startling them, and keep them out of bright light.
βLaboratory Alterations:β Opiates can increase biliary tract pressure, potentially elevating plasma amylase and lipase values for up to 24 hours post-administration.
Drug interactions
May inhibit fentanyl metabolism, increasing risk of toxicity
Additive CNS and respiratory depressant effects
Opiates may decrease diuretic efficacy in congestive heart failure patients
May inhibit fentanyl metabolism
Severe and unpredictable opiate potentiation; generally not recommended within 14 days of MAOI use
Fentanyl may enhance neuromuscular blockade
High fentanyl doses combined with nitrous oxide may cause cardiovascular depression
May increase the metabolism of fentanyl, reducing its efficacy
May increase the metabolism of fentanyl
Fentanyl may exacerbate the effects of tricyclic antidepressants
Opiates may potentiate anticoagulant activity
Reduces the dose requirement for other anaesthetic agents
Monitoring
- Analgesic efficacy (pain scoring)
- Heart rate (monitor for bradycardia)
- Respiratory rate and depth
- Body temperature (monitor for fever which increases patch absorption)
- Neurologic status (sedation, dysphoria)
- Heart rate and rhythm (monitor for bradycardia)
- Blood pressure
- Adequacy of analgesia
- Body temperature (avoid external heat on patches)
Pharmacokinetics
Half-life
Absorption
Transdermal absorption is highly variable among patients. Cats tend to achieve therapeutic levels faster than dogs. Dogs require patch application 12-24 hours in advance; cats 6-24 hours; horses ~6 hours. Febrile patients may have significantly increased absorption.
Distribution
Rapidly distributes due to high lipophilicity. Exhibits a large volume of distribution (5 L/kg in dogs).
Metabolism
Hepatic metabolism (implied by interactions with CYP inhibitors like azole antifungals and macrolides).
Elimination
Total clearance in dogs is 78 mL/min/kg.
Overdose
βClinical Signs of Overdose:β Profound respiratory and/or CNS depression, cardiovascular collapse, bradycardia, hypothermia, tremors, neck rigidity, and seizures. Newborns are particularly susceptible.
βTreatment:β
- Naloxone is the specific reversal agent of choice for treating respiratory depression.
- Because naloxone's duration of action is often shorter than fentanyl's, repeated doses or a CRI of naloxone may be required.
- Patients must be closely monitored for re-narcotization.
- Mechanical respiratory support should be instituted in cases of severe respiratory depression.
Available products
Formulations
- Injectable solution (0.05 mg/mL)
- Transdermal patch (12, 25, 50, 75, 100 mcg/hr)
- Buccal tablets
- Transmucosal lozenges
- Iontophoretic transdermal system
- Oral tablets: 100 ΞΌg, 200 ΞΌg, 400 ΞΌg, 600 ΞΌg, 800 ΞΌg
- Injectable solution: 50 ΞΌg/ml
- Transdermal patches: 12.5 ΞΌg/h, 25 ΞΌg/h, 50 ΞΌg/h, 75 ΞΌg/h, 100 ΞΌg/h
Veterinary
- None (No veterinary-labeled products available)
- Fentadon 50 ΞΌg/ml solution
Human-labeled
- Fentanyl Buccal Tablets: 100 mcg, 200 mcg, 400 mcg, 600 mcg, & 800 mcg (Fentora)
- Fentanyl Injectable: 0.05 mg/mL (50 mcg/mL) in various ampules and vials (Sublimaze)
- Fentanyl Transdermal System: 12 mcg/hr, 25 mcg/hr, 50 mcg/hr, 75 mcg/hr, 100 mcg/hr (Duragesic)
- Fentanyl Iontophoretic Transdermal System: 40 mcg/dose (Ionsys)
- Fentanyl Transmucosal System (Lozenges): 200 mcg to 1600 mcg (Actiq)
- Durogesic patches
- Fentanyl patches/tablets
- Fentora tablets
- Sublimaze solution
Regulatory status
POM-V CD SCHEDULE 2
POM-V CD SCHEDULE 2, POM CD SCHEDULE 2
No regulatory data for: πΊπΈ US Β· ππ° HK Β· πΉπΌ TW Β· π―π΅ JP Β· π°π· KR Β· π¦πΊ AU
Storage & stability
Transdermal patches: Store below 25Β°C (77Β°F). Apply immediately after removing from the sealed package. Do not cut patches. Buccal tablets: Store at room temperature; do not refrigerate or freeze. Injectable: Protect from light; it is hydrolyzed in acidic solutions.
Client information
βImportant Safety Information for Pet Owners:β
- βExtreme Caution with Children and Pets:β Fentanyl is a highly potent narcotic. If a patch falls off or is removed by the pet, it can be fatal if chewed or swallowed by a child or another animal. Dispose of used patches securely (e.g., folding the sticky sides together and flushing down the toilet or returning to the clinic).
- βAccidental Human Contact:β If you accidentally touch the sticky side of the patch or the gel, wash your hands immediately with plain water ONLY. Do NOT use soap, alcohol, or hand sanitizers, as these can increase the absorption of the drug through your skin.
- βNO Heat Sources:β Never allow your pet to lie on a heating pad, heated blanket, or in direct intense sunlight while wearing the patch. Heat causes the drug to be released rapidly, which can cause a fatal overdose.
- βDelayed Effect:β The patch takes time to start working (12-24 hours in dogs, 6-12 hours in cats). Your veterinarian may prescribe other pain medications to bridge this gap.
- βMonitoring:β Watch your pet closely for extreme lethargy, severe changes in breathing (very slow or shallow), or unusual agitation. Contact your veterinarian immediately if these occur.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerβs current label.