Opioid Analgesic (Ultra-Short Acting) Pregnancy: Caution — crosses placenta; neonatal respiratory depression if used intrapartum

Alfentanil

Brand names: Rapifen

Adult dose

Dose: Bolus: 0.5–1 mg IV; Induction supplement: 7–20 mcg/kg; Infusion: 25–100 mcg/kg/hour

Route: IV

Frequency: Bolus or continuous infusion

Max: Titrated to clinical response

Fast-onset, short-duration opioid. Onset 1 min; duration 10–20 min (single bolus). Used as induction supplement and for brief procedures. Context-sensitive half-time increases with prolonged infusion — less suitable than remifentanil for long cases.

Paediatric dose

Dose: 5–20 mcg/kg

Route: IV

Frequency: Bolus

Max: Titrated to effect

Intraoperative supplement: 5–20 mcg/kg under specialist guidance.

Dose adjustments

Renal

No dose adjustment required — hepatically metabolised.

Hepatic

Caution in severe hepatic impairment — reduced clearance, prolonged effect.

Paediatric weight-based calculator

Patient weight (kg)

Intraoperative supplement: 5–20 mcg/kg under specialist guidance.

Clinical pearls

Antidote: naloxone 0.4–2 mg IV — titrate carefully
Chest wall rigidity ('wooden chest') with rapid high-dose bolus — requires NMB to ventilate
Preferred over fentanyl for very short procedures; remifentanil preferred for longer cases requiring rapid recovery

Contraindications

Respiratory depression without ventilatory support
MAOIs within 14 days

Side effects

Respiratory depression
Chest wall rigidity (rapid bolus)
Nausea/vomiting
Bradycardia
Hypotension

Interactions

MAOIs (potentially fatal — contraindicated within 14 days)
CYP3A4 inhibitors — erythromycin/fluconazole (significantly increase plasma levels)
CNS depressants (additive)

Monitoring

SpO2, RR, BP, HR
Level of consciousness

Reference: BNFc; BNF 90; Stoelting's Pharmacology and Physiology in Anaesthetic Practice; AAGBI Guidelines. Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways