Fentanyl
Strong opioid used in restricted indications
Mechanism of action: mu-opioid agonist.
Presentation: transdermal patch, lozenge, solution for injection. (Buccal and sublingual tablet non-formulary in OUH).
Dose: Morphine and oxycodone are the preferred strong opioids
Fentanyl is approx. 80 times more potent than morphine
Suggested initial dose: the lowest strength patch is 12 microgram/hour patch (equivalent to 45mg morphine per day). For use only in adults over 50kg with normal hepatic and renal function if they are unable to absorb enteral analgesia, have constant (not intermittent) pain, and have normal skin perfusion (i.e., are not pyrexial, hypovolaemic or sweaty). [Principles of patches]
Fentanyl patches should not be initiated for patients with acute pain. The patches take 24 hours to reach steady state and do not allow for fluctuations in pain.
Some patients may be using fentanyl patches on admission. Please contact the pain team for advice if such a patient is acutely unwell as to whether the fentanyl patches should be continued during a hospital stay, how to monitor the patient, and how to provide alternative opioid. Do not apply more than one patch at a time: using more than one patch could result in a fatal overdose. Make sure the old patch is removed before the new patch is put on.
In the OUHFT, fentanyl PCA is only to be used in renal and transplant wards or critical care areas, and is occasionally used in obstetric areas. [Starting a PCA]
Co-prescribe prn Naloxone
Absorption: Bioavailability 92% following transdermal administration and 50% following buccal administration. Oral absorption poor: 30%
Protein binding: 80%
Metabolism: Fentanyl is metabolized primarily via CYP3A4 to inactive norfentanyl.
Elimination: Fentanyl is excreted in urine, mostly as metabolites
Half-life: 7 hours; but 16-25 hours after transdermal application
Further prescribing information (side effects, contraindications, interactions):