Remifentanil
**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.
Mecanismo: 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).
Dosificación por especie
- 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 · In propofol-anesthetized (0.3 mcg/kg/min) cats.
- Analgesic adjunct to general anesthesia · 4 micrograms/kg bolus IV, followed by 6-20 micrograms/kg/hr CRI. · IV · CRI · Do not confuse mcg/kg/hr with mcg/kg/min.
- 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 · Do not confuse mcg/kg/hr with mcg/kg/min.
Las dosis son una referencia clínica para veterinarios colegiados. Confirme siempre con la ficha técnica vigente y el paciente individual.
Vías de administración
Contraindicaciones
- Hypersensitivity to remifentanil or other fentanyl analogs
- Epidural or intrathecal administration (contraindicated due to the presence of glycine in the formulation)
Efectos adversos
- Respiratory depression
- Apnea
- Bradyarrhythmias
- Hypotension
- Hyperthermia (noted in cats)
- Anaphylaxis (rare)
Interacciones farmacológicas
- CNS Depressants (e.g., propofol, isoflurane, thiopental) · Additive CNS and respiratory depression; remifentanil significantly reduces MAC and induction agent requirements.
- Diuretics · Opiates may decrease diuretic efficacy in patients with congestive heart failure.
- Monoamine Oxidase Inhibitors (e.g., amitraz, selegiline) · Severe and unpredictable opiate potentiation may occur; use is generally not recommended if an MAOI has been used within 14 days.
- Skeletal Muscle Relaxants · Remifentanil may enhance neuromuscular blockade.
- Nitrous Oxide · High doses of remifentanil combined with nitrous oxide may cause cardiovascular depression.
- Tricyclic Antidepressants (e.g., clomipramine, amitriptyline) · May exacerbate the effects of tricyclic antidepressants.
- Warfarin · Opiates may potentiate anticoagulant activity.
Monitorización
- 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)
Sobredosis
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**: 1. **Discontinue drug administration immediately.** 2. 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. 3. Administer IV fluids, and use **glycopyrrolate or atropine** to manage bradycardia or hypotension. 4. **Naloxone** may be used to reverse mu-opioid activity, but caution is advised as it can lead to acute pain and sympathetic hyperactivity.
La referencia de fármacos de VetSheet está destinada a veterinarios colegiados como apoyo a la decisión clínica, no sustituye el juicio profesional ni la ficha técnica vigente del fabricante.