Title: Alfentanil
CAS Registry Number: 71195-58-9
CAS Name: N-[1-[2-(4-Ethyl-4,5-dihydro-5-oxo-1H-tetrazol-1-yl)ethyl]-4-(methoxymethyl)-4-piperidinyl]-N-phenylpropanamide
Additional Names: N-[1-[2-(4-ethyl-5-oxo-2-tetrazolin-1-yl)ethyl]-4-(methoxymethyl)-4-piperidyl]propionanilide
Molecular Formula: C21H32N6O3
Molecular Weight: 416.52
Percent Composition: C 60.56%, H 7.74%, N 20.18%, O 11.52%
Literature References: Tetrazole derivative of fentanyl, q.v. Prepn: F. Janssens, DE 2819873; idem, US 4167574 (1978, 1979 both to Janssen); F. Janssens et al., J. Med. Chem. 29, 2290 (1986). Determn in human plasma by GC: T. J. Gillespie et al., J. Anal. Toxicol. 5, 133 (1981); by radioimmunoassay: M. Michaels et al., J. Pharm. Pharmacol. 35, 86 (1983). Pharmacology in animals: C. J. E. Niemegeers, P. A. J. Janssen, Drug Dev. Res. 1, 83 (1981); in humans: B. Kay, B. Pleuvry, Anaesthesia 35, 952 (1980). Cardiovascular effects during surgery: P. S. Sebel et al., Br. J. Anaesth. 54, 1185 (1982). Clinical evaluation as analgesic component of anesthesia: B. Kay et al., Ann. R. Coll. Surg. Engl. 65, 316 (1983); as anesthetic induction agent: J. Nauta et al., Anesth. Analg. 61, 267 (1982); M. E. Sinclair, G. M. Cooper, Anaesthesia 38, 435 (1983). Review of clinical pharmacokinetics: L. E. Mather, Clin. Pharmacokinet. 8, 422 (1983); of clinical trials of alfentanil and sufentanil: S. De Lange, Mt. Sinai J. Med. 50, 312 (1983).
Derivative Type: Hydrochloride monohydrate
CAS Registry Number: 70879-28-6
Additional Names: Alfentanil hydrochloride
Manufacturers' Codes: R-39209
Trademarks: Rapifen (Janssen-Cilag); Alfenta (Janssen)
Molecular Formula: C21H32N6O3.HCl.H2O
Molecular Weight: 470.99
Percent Composition: C 53.55%, H 7.49%, N 17.84%, O 13.59%, Cl 7.53%
Properties: Crystals from 2-propanone, mp 140.8° (Janssens, 1979); also reported as crystals from acetone, mp 138.4° (Janssens, 1986). Sol in water. LD50 in rats, dogs (mg/kg): 47.5, 20 i.v. (Niemegeers, Janssen).
Melting point: mp 140.8° (Janssens, 1979); mp 138.4° (Janssens, 1986)
Toxicity data: LD50 in rats, dogs (mg/kg): 47.5, 20 i.v. (Niemegeers, Janssen)
NOTE: This is a controlled substance (opiate): 21 CFR, 1308.12.
Therap-Cat: Analgesic (narcotic).
Therap-Cat-Vet: Analgesic (narcotic).
Keywords: Analgesic (Narcotic).
Alfimeprase Alfuzosin Algestone Algestone Acetophenide Algin

Systematic (IUPAC) name
Clinical data
Trade names Alfenta
AHFS/ Micromedex Detailed Consumer Information
MedlinePlus a601130
Legal status Controlled (S8) (AU) Class A (UK) Schedule II (US)
Routes Intravenous
Pharmacokinetic data
Bioavailability 100%
Protein binding 92%
Metabolism Hepatic
Half-life 90–111 minutes
CAS number 71195-58-9 YesY
ATC code N01AH02
PubChem CID 51263
DrugBank DB00802
ChemSpider 46451 YesY
KEGG D07122 YesY
Chemical data
Formula C21H32N6O3 
Mol. mass 416.517 g/mol
Physical data
Melt. point 140.8 °C (285 °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.[1] 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 anesthesiologists 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.[2]

Alfentanil was discovered at Janssen Pharmaceutica in 1976.