Anaes · Anaesthetic adjuncts
Alfentanil
Also known as Fastest-onset fentanyl-family opioid · Rapid-onset short-duration phenylpiperidine
Alfentanil is a synthetic short-acting fentanyl derivative with the least potency versus fentanyl/sufentanil, the fastest onset and the shortest duration, favoured for shorter procedures requiring swift alterations and used as primary agent in high-dose cardiac surgery, FDA-approved for adults and children for general anaesthesia and monitored anaesthesia care (Moman StatPearls). Its rapid onset with reduced lipid solubility and less cumulation versus fentanyl is trial-observed (Weninger 62-patient ESWL comparison); simulations show a transient peak after single bolus with rapid effect-site decrease after prolonged use for long operations (Shafer). Other anilidopiperidines depend on hepatic biotransformation while remifentanil uses widespread esterases with a flat 3.2-minute half-time even after 8-hour infusion (Beers); context-sensitive half-time is the 50-percent decline time after infusions of given duration (Hughes). pKa, potency fractions, minute-durations, CYP3A4, inactive-metabolite renal safety and no-histamine points are taught/formulary — confirm local protocol.
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- Alfentanil's rapid onset is due to its LOW pKa (about 6.5) — most of the drug is un-ionised at physiological pH and reaches the brain effect site quickly; this also means respiratory depression can appear within about 1 minute of an IV bolus.
- Although short-acting after a single bolus, alfentanil's CONTEXT-SENSITIVE HALF-TIME RISES with prolonged infusion (accumulation) — it is NOT ultra-short like remifentanil for prolonged use.
- Like fentanyl, high-dose alfentanil can cause CHEST-WALL RIGIDITY and dose-dependent respiratory depression — reverse with naloxone.
Meet the patient
A 55-year-old man is booked for a DC cardioversion that will take ninety seconds. You need an opioid that peaks at the shock and is gone before he reaches recovery — not a long-acting tail that keeps him ventilated.[1][2]
The question that decides every opioid choice is threefold: how fast does it peak, how long does it last, and does it accumulate if you repeat it? Alfentanil answers the first two better than any classic bolus opioid — fastest onset and shortest duration (Moman) with transient peak after single bolus on simulation (Shafer) — and fails the third if you push it past a brief case.[1][2]
References5ShowHide
- [1]Moman RN, et al. Alfentanil. StatPearls, 2024.PMID 29261876
- [2]Shafer SL, et al. Pharmacokinetics, pharmacodynamics, and rational opioid selection. Anesthesiology, 1991.PMID 1824743
- [3]Hughes MA, et al. Context-sensitive half-time in multicompartment pharmacokinetic models for intravenous anesthetic drugs. Anesthesiology, 1992.PMID 1539843
- [4]Beers R, et al. Remifentanil update: clinical science and utility. CNS Drugs, 2004.PMID 15581380
- [5]Weninger E, et al. [A comparative study of intravenous opioid analgesia. Sufentanil and alfentanil for extracorporeal shock-wave lithotripsy in urologic patients]. Anaesthesist, 1996.PMID 8702050