Fentanyl Citrate

• Fentanyl Citrate is a synthetic opioid acting on μ-receptors, offering strong pain relief with fast onset.
• It provides rapid, potent analgesia for surgery, cancer pain, and anesthesia.

Chemical Formula:

• C₂₂H₂₈N₂O·C₆H₈O₇

Mechanism of Action:

• Full μ-opioid receptor agonist
• 50–100× more potent than morphine
• High lipophilicity → rapid onset and short duration

Uses of Fentanyl Citrate:

• Severe acute pain
• Surgical anesthesia (IV, transdermal)
• Breakthrough cancer pain (lozenges, sprays)
• Epidural analgesia

Side Effects:

• Profound respiratory depression
• Chest wall rigidity (with rapid IV)
• Sedation
• Nausea, bradycardia

SAR of Fentanyl:

1. Anilidopiperidine core:

   • Required for strong μ-receptor binding.

2. Phenyl ring on piperidine:

   • Enhances binding via π-π stacking with receptor.

3. Amide linkage (anilide):

   • Stabilizes the conformation of the molecule, critical for activity.

4. Lipophilicity:

   • High lipid solubility → rapid onset and short duration (suitable for IV use).

5. Flexible side chain:

   • Allows proper receptor fit.

6. N-phenethyl group:

   • Strongly enhances μ-receptor affinity and potency.

Synthesis of Fentanyl:

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