GasGasGas - The FRCA Primary Exam Podcast GasGasGas - Alfentanil for the FRCA Primary Exam
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May 1, 2025 Discover the fascinating world of alfentanil, a crucial short-acting μ-opioid. Learn about its 1976 origins and why it's a go-to for rapid-sequence inductions. Delve into its therapeutic index and clinical uses, including acute pain management and obstetrics. Explore the unique pharmacokinetics that give it a faster onset than fentanyl. Plus, hear about the potential side effects and safe dosing practices. This insightful discussion is both educational and entertaining for anyone in anaesthetic practice.
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From Pethidine To Alfentanil
- Paul Janssen tinkered with pethidine and discovered fentanyl in 1959, spawning many analogues.
- Alfentanil was later discovered in 1976 at Janssen and is a shorter-acting derivative of fentanyl.
Unionised Fraction Drives Fast Onset
- Alfentanil has a pKa of 6.5 and is ~89% unionised at pH 7.4, driving rapid onset despite lower lipid solubility.
- This makes alfentanil onset faster than fentanyl, typically under 90 seconds.
Use Alfentanil For Modified RSI
- Use alfentanil for modified RSI and short suppression of laryngoscopy responses when you need a fast-onset opioid.
- Dose 30–50 µg/kg to blunt intubation haemodynamics and avoid >500 µg if you want to preserve spontaneous breathing.