Fentanyl is a potent synthetic opioid agonist that belongs to the phenylpiperidine derivative class of drugs. It is structurally related to meperidine and is known for its remarkable potency, being 75 to 125 times more potent than morphine. Fentanyl was first synthesized in 1960 by Janssen Pharmaceutica and is commonly available as its citrate salt under the trade name Sublimaze.
Pharmacokinetics
| Characteristic | Description |
|---|---|
| Potency | 75 to 125 times more potent than morphine |
| Onset and Duration of Action | Rapid onset, shorter duration compared to morphine |
| Blood-Brain Barrier Penetration | Rapid due to high lipid solubility |
| Tissue Distribution | Extensive distribution into highly vascular tissues |
| Metabolism | Extensively metabolized by N-demethylation |
| Elimination Half-Time | Longer than morphine due to larger volume of distribution |
| Context-Sensitive Half-Time | Prolongs with prolonged infusion |
Note: Fentanyl has a rapid onset of action due to its high lipid solubility, which facilitates its passage across the blood-brain barrier. It has a longer elimination half-time than morphine, primarily due to its larger volume of distribution.
Clinical Uses
| Clinical Application | Recommended Doses and Routes |
|---|---|
| Analgesia | – Low doses (1 to 2 μg/kg IV) for analgesia |
| Adjunct to Inhalation Anesthetics | – As an adjuvant to inhaled anesthetics to blunt circulatory responses to laryngoscopy or surgical stimulation |
| Surgical Anesthesia | – Large doses (50 to 150 μg/kg IV) for surgical anesthesia |
| Transmucosal Preparations | – Oral transmucosal fentanyl for preoperative sedation and induction of anesthesia |
| Transdermal Patch | – Long-term, sustained analgesia for chronic pain (e.g., cancer-related pain) |
Note: Fentanyl can be administered in various ways depending on the clinical need, including intravenous, transmucosal, and transdermal routes.
Side Effects
| Side Effect | Description |
|---|---|
| Respiratory Depression | Can lead to hypoventilation |
| Cardiovascular Effects | – Bradycardia – Hypotension (minimal histamine release) |
| Seizure Activity | Rare but reported following rapid IV administration |
| Somatosensory Evoked Potentials | May produce changes but typically do not interfere with monitoring |
| Intracranial Pressure | Modest increases in ICP, especially in head injury patients |
| Drug Interactions | – Potentiates the effects of benzodiazepines – Decreases propofol dose requirements |
Note: Fentanyl can cause respiratory depression, and caution is needed when combining it with other central nervous system depressants.
