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Systematic (IUPAC) name
Clinical data
Trade names Alfenta
AHFS/ Micromedex Detailed Consumer Information
MedlinePlus a601130
Legal status
Routes of
Pharmacokinetic data
Bioavailability 100%
Protein binding 92%
Metabolism Hepatic
Biological half-life 90–111 minutes
Duration of action 15 min[1]
CAS Number 71195-58-9 YesY
ATC code N01AH02
PubChem CID: 51263
DrugBank DB00802 YesY
ChemSpider 46451 YesY
KEGG D07122 YesY
Chemical data
Formula C21H32N6O3
Molecular mass 416.517 g/mol
Physical data
Melting point 140.8 °C (285.4 °F)
 YesY (what is this?)  (verify)

Alfentanil (R-39209, trade name Alfenta, Rapifen in Australia) is a potent but short-acting synthetic opioid analgesic drug, used for anaesthesia in surgery. It is an analogue of fentanyl with around 1/4 to 1/10 the potency of fentanyl and around 1/3 of the duration of action, but with an onset of effects 4x faster than fentanyl.[2] Alfentanil has a pKa of approximately 6.5, which leads to a very high proportion of the drug being uncharged at physiologic pH. This unique characteristic is responsible for its rapid onset. It is an agonist at mu opioid receptors.

While alfentanil tends to cause fewer cardiovascular complications than other similar drugs such as fentanyl and remifentanil, it tends to give stronger respiratory depression and so requires careful monitoring of breathing and vital signs. Almost exclusively used by anesthesia providers during portions of a case where quick, fast acting (though not long lasting) pain control is needed (i.e. during a nerve block, head pinning etc..) Alfentanil is administered by the parenteral (injected) route for fast onset of effects and precise control of dosage.

Alfentanil is a restricted drug which is classified as Schedule II in the USA, according to the U.S. DEA website.[3]

Alfentanil was discovered at Janssen Pharmaceutica in 1976.

Side effects of fentanyl analogs are similar to those of fentanyl itself, which include itching, nausea and potentially serious respiratory depression, which can be life-threatening. Fentanyl analogs have killed hundreds of people throughout Europe and the former Soviet republics since the most recent resurgence in use began in Estonia in the early 2000s, and novel derivatives continue to appear.[4]


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