Alfentanil

• Potent, Rapid-Onset, Short-Acting Opioid: Used mostly in anesthesia and procedural sedation rather than routine ICU analgesia
• Ultra-Fast Onset: Peak effect within ~1–2 minutes IV with shorter duration than fentanyl due to smaller volume of distribution and faster offset
• Intubation Facilitation: Provides intense but brief analgesia and blunts sympathetic responses to laryngoscopy, intubation, or short procedures when given as a bolus
• Major Risks: Profound respiratory depression, chest wall rigidity (at high doses/rapid administration), hypotension, and bradycardia, especially when combined with other sedatives
• Limited ED Use: Less commonly used in many EDs compared with fentanyl or remifentanil, but may be encountered in OR or transport of anesthetized patients

• Generic Name: Alfentanil hydrochloride
• Brand Names: Alfenta, generics (availability may vary)

Short-acting synthetic opioid analgesic; fentanyl analog

Mechanism of Action:

• Highly selective μ-opioid receptor agonist, similar to fentanyl, acting in the CNS and spinal cord to modulate pain pathways
• Activation of μ-receptors inhibits adenylate cyclase, decreases cAMP, opens K⁺ channels, and closes voltage-gated Ca²⁺ channels → reduced neurotransmitter release and neuronal excitability
• Produces analgesia, sedation, respiratory depression, bradycardia, and reduced sympathetic response to painful stimuli

Pharmacokinetics (IV):

• Onset: Very rapid, with peak effect generally within 1–2 minutes of IV administration
• Distribution: Smaller volume of distribution than fentanyl → faster decline in effect-site concentration after bolus dosing
• Metabolism: Primarily hepatic via CYP3A4 to inactive metabolites
• Elimination half-life: ~1–2 hours, but context-sensitive half-time is relatively short for brief infusions; longer with prolonged high-dose infusions
• Duration: Clinically significant analgesia after a bolus is usually 5–15 minutes, depending on dose and patient factors

Available Forms:

• IV injection: Common concentration 500 mcg/mL (0.5 mg/mL) in 2 mL or 10 mL vials
• Typically administered undiluted or diluted in small volumes for bolus dosing; continuous infusion sometimes used in anesthesia settings

Adult Dosing (Anesthesia-Focused) – Always Follow Local Protocols:

Contraindications:

• Significant respiratory depression or acute severe asthma without ventilatory support
• Known hypersensitivity to alfentanil, fentanyl analogs, or formulation components

Major Precautions:

• Risk of profound respiratory depression and apnea, especially when combined with benzodiazepines, propofol, or other CNS depressants
• Rapid IV administration or high doses may cause chest wall rigidity and difficulty ventilating; neuromuscular blockade and mechanical ventilation may be required
• Bradycardia and hypotension, particularly in patients with compromised cardiac reserve or hypovolemia
• Use caution in patients with increased intracranial pressure or traumatic brain injury: hypercapnia from hypoventilation may worsen ICP
• Tolerance and physical dependence can develop with repeated dosing or prolonged infusions

Common:

• Respiratory depression, hypoventilation
• Nausea, vomiting
• Bradycardia, hypotension
• Pruritus, flushing

Serious:

• Apnea and respiratory arrest
• Chest wall rigidity leading to difficult ventilation
• Severe hypotension or bradycardia requiring intervention
• Anaphylactoid reactions

Clinical Monitoring:

• Continuous pulse oximetry and cardiorespiratory monitoring during and after administration
• Ventilatory status: respiratory rate, tidal volumes, ETCO₂ if available
• Hemodynamics: heart rate and blood pressure, especially in patients with limited reserve
• Level of consciousness and pain scores when used for analgesia/sedation

• Anesthetic induction: Analgesia and blunting of sympathetic response during intubation as part of a balanced anesthetic technique
• Short procedures: Intense but brief analgesia for painful manipulations, short endoscopic procedures under monitored anesthesia care
• Procedural sedation: Adjunct to other sedatives (e.g., propofol, midazolam) in OR or monitored settings with full airway/ventilation backup
• ICU procedures: Bedside bronchoscopy when anesthesiology is involved and ultra-fast offset is desired
• Note: Rarely used for continuous analgesia in ICU; other opioids (fentanyl, hydromorphone) are generally preferred

• 1. Lexicomp. (2024). Alfentanil: Drug information. Wolters Kluwer.
• 2. Stoelting, R. K., & Hillier, S. C. (2006). Pharmacology and physiology in anesthetic practice (4th ed.). Lippincott Williams & Wilkins.