Alfentanil

ED / ICU / Transport

• Brief painful procedures in adults: Alone or with a sedative such as propofol, it supplies the analgesia for moderate procedural sedation. Only clinicians trained in airway rescue give it. Outside MAC that use is off-label and protocol-dependent.
• Laryngoscopy and intubation with controlled ventilation: It blunts the sympathetic surge (hypertension, tachycardia) with laryngoscopy. The label covers general anesthesia. For ED or transport RSI, it is off-label. See RSI.
• Encountered at transfer: You rarely use it for ICU analgesia or sedation in the US. Most often you meet it in the OR, the endoscopy suite, or on an interfacility transfer of an anesthetized patient.

Other Uses

• Monitored anesthesia care (MAC): analgesic component for sedated, responsive, spontaneously breathing patients (FDA-labeled)
• Balanced general anesthesia: incremental analgesic adjunct for short procedures (FDA-labeled)
• Maintenance of general anesthesia: continuous-infusion analgesia with controlled ventilation (FDA-labeled)
• Induction of general anesthesia: primary anesthetic in intubated, ventilated surgical patients (FDA-labeled)
• GI endoscopy: opioid adjunct to propofol sedation to reduce movement and propofol dose (off-label outside MAC)
• Bronchoscopy sedation: adjunct to propofol; reduces coughing and propofol dose but increases hypoxemia (off-label outside MAC)

Weight, physical status, other drugs and the procedure all change the dose (FDA label, Dosage section). Follow local protocol.

Available Forms

• IV injection: 500 mcg/mL (0.5 mg/mL) alfentanil base, preservative-free single-use ampules: 2 mL (1,000 mcg), 5 mL (2,500 mcg), 10 mL (5,000 mcg), 20 mL (10,000 mcg)
• Small volumes: 10 mcg/kg for 70 kg is 1.4 mL. The label advises a tuberculin syringe for volumes this small.

Adult Dosing

Dosing weight is lean body weight when the patient is more than 20% above ideal body weight. Older adults start with an initial dose up to 40% lower.

Pediatric Dosing

Continuous Infusion

Preparation & Administration

• Push rate: induction doses over 3 min; other boluses slowly (about 30 sec). Slow pushes reduce rigidity.
• Dilution: NS, D5NS, D5W or LR at 25–80 mcg/mL; e.g., 20 mL in 230 mL gives 40 mcg/mL. UK label: use within 24 hr of preparation (US label gives no limit); follow institutional policy.
• Pump requirement: infusions on a programmable pump with a drug library.
• Ready at the bedside: O₂, suction, BVM, airway kit, naloxone, neuromuscular blocker.

Contraindications

• Hypersensitivity to alfentanil: the only contraindication on the US label. Known hypersensitivity to other opioids calls for caution.
• UK label adds: obstructive airways disease or respiratory depression if not ventilated; MAOIs within 2 weeks; labor or before cord clamping (relative in US practice); known intolerance to alfentanil or other opioids (morphinomimetics)

Precautions

• Limited respiratory reserve (COPD, hypoxia, hypercapnia, frail or older adults): usual doses can cause apnea.
• Raised ICP or head injury: CO₂ retention raises ICP. It also masks the neurologic exam. Avoid rapid boluses. A transient MAP drop can lower cerebral perfusion pressure.
• Hypovolemia: Induction drops the pressure. Give fluids first.
• Bradycardia can progress to asystole. Have atropine ready.
• Opioid-induced hyperalgesia: pain gets worse on the drug, or normally painless stimuli start to hurt. It is reported after short and longer use.
• Tolerance and physical dependence can follow prolonged infusions. Don't stop abruptly in a dependent patient: expect withdrawal.
• Other: seizure disorders, biliary disease (sphincter of Oddi spasm).

Hold / Reassess If

These thresholds are examples. Follow local protocol.

• Apnea, SpO₂ <90%, EtCO₂ up >10 mmHg or lost capnogram: stop, stimulate, O₂, ventilate
• Rigidity (cannot ventilate): neuromuscular blocker and ventilate
• SBP <90 mmHg or bradycardia with hypotension: stop; fluids, atropine or vasopressor
• No purposeful response during MAC: no further doses

Common

• Nausea (28%), vomiting (18%)
• Hypertension (18%), bradycardia (14%), tachycardia (12%), hypotension (10%)
• Chest wall rigidity (17%, mostly induction doses)
• Apnea and dizziness (3–9%)

Serious / Life-Threatening

Overdose & Toxicity Management

• Signs: apnea, coma, pinpoint pupils (dilated if hypoxic), bradycardia, hypotension, hypoglycemia, pulmonary edema.
• Management: airway and ventilation first; neuromuscular blocker if rigidity prevents ventilation; ACLS for arrest.
• Antidote: naloxone titrated: adult 0.1–0.2 mg IV every 2–3 min; child 0.005–0.01 mg IV increments (not per kg) every 2–3 min for postoperative depression, or 0.01 mg/kg IV initial for overdose, then 0.1 mg/kg if response is inadequate (naloxone label); follow PALS and local protocol. Large naloxone doses cause pain, hypertension, pulmonary edema and withdrawal. Nalmefene is a longer-acting alternative named in the alfentanil label. Follow its labeling and local protocol.
• Re-sedation: after large doses or infusions, respiratory depression can outlast the naloxone.

Clinically Significant Interactions

IV Compatibility

• Diluents: NS, D5NS, D5W, LR; UK label: use dilutions within 24 hr; follow institutional policy.
• Line: dedicated line for infusions where possible.
• Verify with an institutional compatibility resource.

• Pediatrics: US label: data are inadequate under 12 years. Young children carry a higher risk of respiratory complications and rigidity. See the Pediatric Dosing table.
• Neonates: clearance and protein binding are lower, so the half-life runs longer and varies widely. Rigidity occurred in 65% of newborns given low doses.
• Pregnancy: US label: may cause fetal harm. In rats, pup birth weight and survival fell. In rabbits it was embryocidal. Both were seen at high multiples of the human dose, with no malformations. Human data are insufficient. It crosses the placenta and can depress the newborn's breathing. Prolonged use causes neonatal withdrawal. Not recommended during labor (US). Contraindicated in labor (UK).
• Lactation: US label: watch the breastfed infant for excess sedation and respiratory depression. UK label: not recommended in nursing women.
• Older Adults: they need a dose about 40% lower and clear the drug more slowly. Reduce the initial dose by up to 40%.
• Renal Impairment: No specific adjustment is established. About 1% leaves the body unchanged, but in renal failure the free (unbound) fraction rises, so effects may be greater. Use caution. Reduce the dose as needed and monitor for respiratory depression, sedation and hypotension.
• Hepatic Impairment: The liver clears it extensively, so the effect may run long. Reduce the dose and monitor.
• Obesity / Dosing Weight: lean body weight when more than 20% above ideal body weight.
• Opioid-Dependent Patients: Reverse with small, titrated naloxone doses. Large ones can trigger acute withdrawal.

• Scope: The label limits use to clinicians trained in IV anesthetics and airway management. EMS or transport use runs only under agency protocol and medical direction. It varies by state and agency protocol.
• Storage & Stability: 20–25 °C (68–77 °F), excursions 15–30 °C (59–86 °F); protect from light; C-II security and witnessed waste.
• Carried Concentration: one strength (500 mcg/mL); label syringes and store apart from fentanyl and sufentanil.
• Post-Procedure Transfers: Delayed respiratory depression is reported after the procedure. Keep SpO₂ and capnography on.
• Infusions in Transport: uncommon; smart pump, dedicated line, confirm mcg/kg/min at handoff.
• Handoff Essentials: time and total dose (mcg/kg), co-sedatives, naloxone given, airway or rigidity events.

Mechanism of Action

• μ-opioid receptor agonist → inhibits pain transmission → analgesia and sedation.
• Brainstem respiratory centers → blunted response to CO₂ → hypoventilation and apnea.
• Cardiovascular effects → bradycardia and peripheral vasodilation → hypotension, especially with co-sedatives.
• GI smooth muscle → slowed motility and sphincter of Oddi spasm; miosis.

Pharmacokinetics

• Half-life: distribution 1 and 14 min; terminal 90–111 min. Infusion length stretches its context-sensitive half-time far less than fentanyl's.
• Metabolism: hepatic, mainly CYP3A4 (intermediate extraction).
• Elimination: metabolites in urine; about 1% unchanged.
• Protein binding / Vd: about 92% bound (alpha-1-acid glycoprotein); Vd 0.4–1 L/kg.

Generic Name

Alfentanil hydrochloride (strength expressed as alfentanil base)

Brand Names

Alfenta (US); current US labeling is Alfentanil HCl Injection, USP. Rapifen (UK, Ireland, New Zealand)

Pharmacologic Class

μ-opioid receptor agonist; synthetic fentanyl derivative

Therapeutic Class

Short-acting opioid analgesic; anesthetic adjunct and induction agent

Controlled Substance

C-II (DEA Schedule II)

ISMP High-Alert

Yes: opioids (all routes) are on the ISMP list of high-alert medications in acute care settings

Look-Alike / Sound-Alike

ALfentanil / fentaNYL; ALfentanil / SUFentanil

Error-Prone Abbreviations to Avoid

Write mcg, never µg or ug; write mcg/kg in full