Product Information

Registration Status: Active

RAPIFEN INJECTION 0.5mg/ML is approved to be sold in Singapore with effective from 1990-03-05. It is marketed by JOHNSON & JOHNSON PTE LTD, with the registration number of SIN04326P.

This product contains Alfentanil 0.5mg/ml in the form of INJECTION. It is approved for INTRAVENOUS use.

This product is manufactured by JANSSEN PHARMACEUTICA NV in BELGIUM, andGlaxoSmithKline (GSK) Manufacturing S.p.A. in ITALY.

It is a Prescription Only Medicine that can only be obtained from a doctor or a dentist, or a pharmacist with a prescription from a Singapore-registered doctor or dentist.



A short-acting opioid anesthetic and analgesic derivative of fentanyl. It produces an early peak analgesic effect and fast recovery of consciousness. Alfentanil is effective as an anesthetic during surgery, for supplementation of analgesia during surgical procedures, and as an analgesic for critically ill patients. [PubChem]


For the management of postoperative pain and the maintenance of general anesthesia.

Mechanism of Action

Opiate receptors are coupled with G-protein receptors and function as both positive and negative regulators of synaptic transmission via G-proteins that activate effector proteins. Binding of the opiate stimulates the exchange of GTP for GDP on the G-protein complex. As the effector system is adenylate cyclase and cAMP located at the inner surface of the plasma membrane, opioids decrease intracellular cAMP by inhibiting adenylate cyclase. Subsequently, the release of nociceptive neurotransmitters such as substance P, GABA, dopamine, acetylcholine and noradrenaline is inhibited. Opioids also inhibit the release of vasopressin, somatostatin, insulin and glucagon. Alfentanil's analgesic activity is, most likely, due to its conversion to morphine. Opioids close N-type voltage-operated calcium channels (OP2-receptor agonist) and open calcium-dependent inwardly rectifying potassium channels (OP3 and OP1 receptor agonist). This results in hyperpolarization and reduced neuronal excitability.


For intravenous injection or infusion only.
* 0.4 to 1 L/kg
The liver is the major site of biotransformation.


* 5 mL/kg/min


Symptoms of overexposure include characteristic rigidity of the skeletal muscles, cardiac and respiratory depression, and narrowing of the pupils.

Active Ingredient/Synonyms

Alfentanilum | Alfentanyl | N-(1-(2-(4-Ethyl-5-oxo-2-tetrazolin-1-yl)ethyl)-4-(methoxymethyl)-4-piperidyl)propionanilide | Alfentanil |

Source of information: Drugbank (External Link). Last updated on: 3rd July 18. *Trade Name used in the content below may not be the same as the HSA-registered product.


  1. Health Science Authority of Singapore - Reclassified POM
  2. Drugbank