Remifentanil
Remifentanil hydrochloride
Also known as: Ultiva · Remicit · GI-87084B · remifentanilo · rémifentanil · remifentanili
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
This is a rate-based continuous infusion (CRI) dose. Calculate the infusion rate; do not use simple weight scaling.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Analgesic adjunct to general anesthesia | 4 micrograms/kg bolus IV, followed by 6-20 micrograms/kg/hr CRI. | IV | CRI | — | 🌎 NA |
| Analgesic adjunct to general anesthesia | 1 microgram/kg IV loading dose slowly over 2-3 minutes, followed by a 0.1-0.2 microgram/kg/minute CRI. | IV | CRI | — | 🌎 NA |
- Analgesic adjunct to general anesthesia: Do not confuse mcg/kg/hr with mcg/kg/min.
- Analgesic adjunct to general anesthesia: Do not confuse mcg/kg/hr with mcg/kg/min.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Analgesic adjunct to general anesthesia | 0.2 micrograms/kg/minute (for OHE) to 0.3 micrograms/kg/minute (to reduce stimulus-induced movement) | IV | CRI | — | 🌎 NA |
- Analgesic adjunct to general anesthesia: In propofol-anesthetized (0.3 mcg/kg/min) cats.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Remifentanil is a potent, ultra-short-acting synthetic mu-opioid agonist structurally related to fentanyl. It is primarily utilized in veterinary medicine as an analgesic adjunct during general anesthesia, particularly for Total Intravenous Anesthesia (TIVA) protocols.
Key pharmacological highlights include:
- Organ-Independent Metabolism: Unlike most opioids that rely on hepatic metabolism and renal excretion, remifentanil is rapidly degraded by nonspecific esterases in the plasma, red blood cells, and tissues. This makes it exceptionally safe for patients with severe hepatic or renal impairment.
- Rapid Offset: Its extremely short duration of action allows for rapid, predictable recovery times regardless of the duration of the infusion, minimizing the prolonged sedation often seen with other opioids.
- Ceiling Effect: Like other opioids used as anesthesia adjuncts, it exhibits a ceiling effect where increased doses do not further enhance analgesia but may increase adverse effects.
Clinical Pearl: Because remifentanil provides no residual post-operative analgesia once the infusion is stopped, it is critical to administer longer-acting analgesics (e.g., NSAIDs, buprenorphine, or regional nerve blocks) prior to the cessation of the remifentanil CRI to prevent acute emergence delirium and pain.
Mechanism of action
Remifentanil acts as a selective agonist at mu-opioid receptors (G-protein coupled receptors) located primarily in the pain-regulating areas of the central nervous system (limbic system, spinal cord, thalamus, midbrain).
Mechanism Pathway: Remifentanil binds to mu-receptors → inhibits adenylate cyclase → decreases intracellular cAMP → promotes opening of potassium channels and inhibits voltage-gated calcium channels → hyperpolarization of nociceptive neurons → suppression of substance P release and profound analgesia.
Metabolism: It is rapidly metabolized via hydrolysis of its propanoic acid-methyl ester linkage by nonspecific blood and tissue esterases (not plasma pseudocholinesterase). The principal carboxylic acid metabolite (GR90291) is virtually inactive (4000 times less potent in dogs).
Safety & warnings
Contraindications
- Hypersensitivity to remifentanil or other fentanyl analogs
- Epidural or intrathecal administration (contraindicated due to the presence of glycine in the formulation)
Adverse effects
- Respiratory depression
- Apnea
- Bradyarrhythmias
- Hypotension
- Hyperthermia (noted in cats)
- Anaphylaxis (rare)
Precautions
Because of the high risk of significant respiratory depression (including apnea) and bradycardia, remifentanil must ONLY be administered in a closely monitored anesthesia care setting with intubation and mechanical ventilation capabilities.
- Administration: Continuous infusions should strictly be administered via a calibrated syringe pump or infusion device.
- Obesity: In morbidly obese patients, the dosage should be calculated based on ideal body weight rather than actual body weight.
- Pregnancy: Weigh potential risks versus benefits. FDA Category C for humans. No teratogenic effects observed in limited animal studies, but fetal respiratory depression is possible.
Drug interactions
Additive CNS and respiratory depression; remifentanil significantly reduces MAC and induction agent requirements.
Opiates may decrease diuretic efficacy in patients with congestive heart failure.
Severe and unpredictable opiate potentiation may occur; use is generally not recommended if an MAOI has been used within 14 days.
Remifentanil may enhance neuromuscular blockade.
High doses of remifentanil combined with nitrous oxide may cause cardiovascular depression.
May exacerbate the effects of tricyclic antidepressants.
Opiates may potentiate anticoagulant activity.
Monitoring
- Cardiac rate and rhythm (ECG)
- Respiratory rate and depth / Capnography (ETCO2)
- Pulse oximetry (SpO2) or arterial blood gas
- Blood pressure (direct or indirect)
- Body temperature (especially in cats)
Pharmacokinetics
Half-life
Absorption
Rapid onset of analgesic action and peak effect (1-3 minutes) following IV administration.
Distribution
Rapidly distributed into the CNS. In dogs, the blood-brain equilibration half-life is 2.3-5.2 minutes. In cats, it has a moderately high volume of distribution (7.6 L/kg in conscious cats, decreasing to 1.65 L/kg under isoflurane anesthesia).
Metabolism
Rapidly metabolized by hydrolysis of the propanoic acid-methyl ester linkage by nonspecific blood and tissue esterases. It is not appreciably metabolized by the liver or by plasma cholinesterase (pseudocholinesterase).
Elimination
High clearance rate (766 mL/min/kg in cats). The principal carboxylic acid metabolite is virtually inactive and excreted.
Overdose
Overdosage manifests as an enhancement of the drug's pharmacological effects.
Clinical Signs:
- Apnea and severe respiratory depression
- Chest-wall rigidity
- Hypoxemia
- Hypotension and severe bradycardia
- Seizures
Treatment:
- Discontinue drug administration immediately.
- Provide supportive therapy, primarily mechanical ventilation and oxygen administration. Because the drug is cleared so rapidly by tissue esterases, this is often the only intervention required.
- Administer IV fluids, and use glycopyrrolate or atropine to manage bradycardia or hypotension.
- Naloxone may be used to reverse mu-opioid activity, but caution is advised as it can lead to acute pain and sympathetic hyperactivity.
Available products
Formulations
- Powder for injection (reconstitution)
Human-labeled
- Remifentanil HCl Powder for reconstitution (IV use only): 1 mg (3 mL vial), 2 mg (5 mL vial), 5 mg (10 mL vial) as Ultiva® or generic equivalents. (Rx, C-II controlled substance)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Prior to reconstitution, store lyophilized powder between 2°-25°C (36°-77°F). To reconstitute, add 1 mL of diluent per mg of drug (yields ~1 mg/mL), then further dilute to 20-250 mcg/mL before administration. Stable for 24 hours at room temperature after dilution with sterile water, D5W, 0.9% NaCl, or 0.45% NaCl. Stable for 4 hours at room temperature when diluted with Lactated Ringer's Solution (LRS), though UK labeling advises against mixing with LRS.
Client information
Remifentanil is an advanced, highly potent pain medication and anesthesia adjunct used exclusively in the veterinary hospital setting.
- Why it is used: It provides profound pain relief during surgical procedures and allows the veterinarian to use lower doses of other anesthetic gases or drugs.
- Fast Acting: Its most unique feature is how quickly it leaves the body. Once the infusion is stopped, the drug wears off in just a few minutes. This allows your pet to wake up from anesthesia much faster and smoother.
- Organ Safe: Because it is broken down by enzymes in the blood and tissues rather than the liver or kidneys, it is exceptionally safe for pets with pre-existing liver or kidney disease.
- Post-Op Pain: Since remifentanil wears off so quickly, your veterinarian will administer longer-acting pain medications before your pet wakes up to ensure they remain comfortable after surgery.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.