Fentanyl is a synthetic opioid used to treat pain and is almost a hundred times more potent than morphine. Fentanyl has a rapid onset of action and lasts only for a short time. The drug is widely used as an anesthetic as well as in the management of breakthrough pain and chronic pain.

Synthesis of fentanyl

The chemical name for fentanyl is ''N''-phenyl-''N''-(1-phenethyl-4-piperidinyl) propanamide and it was first synthesized by Janssen Pharmaceutica using four steps, which are described below:

• Condensation with analine gave N-benzyl-4-piperidone which was then reduced with LAH
• The resulting product underwent acylation with propionic anhydride
• The 1-benzyl group was deprotected through hyrdrogenation at 1atm
• Finally, the Finkelstein reaction was performed.

Fentanyl analogues

The wide popularity of fentanyl as a potent analgesic in the medical and healthcare settings, led to the development of several fentanyl analogues. Some of these include:
 

• Alfentanil sold under the brand name Alfenta. This is a very short acting drug, that lasts for around 5 to 10 minutes.
• Sufentanil sold under the brand name Sufenta. This is nearly ten times more potent that fentanyl and is widely used in heart surgery.
• Remifentanil sold under the brand name Ultiva. This drug has a very short onset and duration of action, even after prolonged infusions.
• Carfentanil sold under the brand name Wildnil. This drug is used to sedate large animals such as elephants.
• Lofentanil is another analogue and is even stronger than carfentanil.

Several fentanyl analogues are used as recreational drugs by drug abusers including 3-Methylfentanyl, Acetyl-α-methylfentanyl, 3-Methylthiofentanyl, α-methylfentanyl, α-methylthiofentanyl, β-hydroxyfentanyl, β-hydroxy-3-methylfentanyl, Thiofentanyl and  ''p''-flurorofentanyl.

Fentanyl dosage forms

Aside from the intravenous form of fentanyl, the drug is also available in the form of a transdermal patch, a buccal (mouth) dissolving tablets, a lollipop and a lozenge. The transdermal patch is used in the management of chronic or long-term pain. The drug is released by the patch into the body fats, from where it slowly moves into the bloodstream over two or three days, therefore providing long-term pain relief.