Fentanyl: Clinical and Pharmacological Profile for Spinal Analgesia

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Fentanyl, a potent narcotic analgesic patented by Janssen Pharmaceuticals in 1963, is primarily used for spinal analgesia. This article explores its clinical considerations, conversion from morphine, and stability in combination with other pharmaceuticals, providing a comprehensive overview for pain management professionals.


Fentanyl is a congener of meperidine, known for its potent analgesic properties and poor hypnotic effects. Its metabolites are inactive, making it an ideal treatment for patients with renal conditions. The drug possesses high solubility, with a maximum concentration of 25,000 mcg per milliliter.

Clinical Considerations

Fentanyl's extreme lipophilicity, especially when compared to morphine sulfate (580:1), results in a more rapid onset and limits spinal distribution. This characteristic is crucial when treating pain at the site of nociception. Literature reviews indicate that fentanyl is 100 times more potent than morphine sulfate for acute pain and 40 to 50 times more potent for chronic pain.

Conversion from Morphine

When converting patients from morphine to fentanyl, Hartley Medical often discusses relevant literature and uses mathematical calculations to determine an initial intraspinal dose. Based on extensive experience, it is observed that practitioners tend to use smaller conversion ratios for fentanyl, such as 1/10 to 1/25 of the daily morphine sulfate dose. Given the broad conversion range, clinicians unfamiliar with intraspinal administration of fentanyl should seek consultation before making conversions. Reported dosing ranges widely, from as low as 4 mcg per day to approximately 5,000 mcg per day.

Maintaining Stability

Fentanyl citrate has been clinically administered intraspinally in combination with various pharmaceuticals. However, there is limited published information on the stability of fentanyl in such combinations. A 1992 study demonstrated that fentanyl 20 mcg/mL is stable with bupivacaine 1.25 mg/mL in normal saline. Additionally, David Shields of the former Elan Pharmaceuticals (now Jazz Pharmaceuticals) found fentanyl to be stable for four weeks when combined with ziconotide. This finding aligns with Hartley Medical's post-infusion analyses, indicating that fentanyl citrate remains stable when combined with other intraspinal pharmaceuticals.


Fentanyl is a highly potent and effective analgesic for spinal administration, particularly suitable for patients with renal conditions due to its inactive metabolites. Its high lipophilicity and rapid onset make it superior to morphine in many cases, though careful consideration is required during conversion and dosing. Stability studies confirm that fentanyl can be safely combined with other intraspinal medications, ensuring its versatility and reliability in pain management protocols.

For more detailed drug reviews and information, visit Hartley Medical's Knowledge Center.