How should conversion from oral morphine to fentanyl patches be carried out?

Please note this medicines Q&A was researched and written over 2 years ago. When using this document it is important to consider new information which may have been published.

  • Explicit guidance on switching opioids is difficult because both the reasons for switching and the patient’s circumstances differ.
  • When initiating transdermal fentanyl in a patient currently treated with oral morphine, the initial dose should be based upon their previous 24-hour opioid requirement.
  • Two parallel dosage conversion ratios are currently recommended by most manufacturers of fentanyl patches.
  • Data from two small studies has shown that conversion of oral morphine to transdermal fentanyl with a ratio of 100:1 is safe and effective. This ratio is endorsed by the Palliative Care Formulary, and is also advised by the British National Formulary for patients who have been on a stable and well-tolerated opioid regimen for a long period and who need opioid rotation.
  • An alternative ratio of oral morphine to transdermal fentanyl of 150:1 is recommended by the PHE Opioids Aware Resource, and is advised by manufacturers for patients who have been stabilised on oral morphine for several weeks and who need opioid rotation.
  • The decision regarding which conversion ratio to use should be based on patient specific factors, the level of patient monitoring which can be offered and the clinical setting.
  • Comparative doses of oral morphine and transdermal fentanyl are given in Tables 1 and 2. These should be used in conjunction with the Summary of Product Characteristics for the fentanyl patch being used.
  • If switching because of possible opioid-induced hyperalgesia, the calculated equivalent dose should be reduced.
  • Patients who are taking a daily dose of morphine that is not exactly equivalent to a particular fentanyl patch strength, will need to be changed to a patch which is either slightly less or slightly more potent than the morphine dose. This will be a clinical decision based on patient specific factors and patients should be monitored.
  • The CQC and NHS England advised to: “formally double check the calculations and where possible have the patient’s dose independently verified”
  • Effective systemic analgesic concentrations of fentanyl are reached less than 12 hours after applying the patch. Guidance is given above regarding the discontinuation of the regular oral morphine dose.
  • Serum fentanyl concentrations increase gradually and level off between 12 and 24 hours. Steady state concentrations are reached by the second 72-hour application. The patient should use breakthrough analgesia as required for the first 3 days particularly the first 24 hours.
  • Patients will require frequent reassessment of efficacy and adverse effects and dose titration after patch initiation or dose change as well as a short acting opioid for breakthrough pain.
  • The dose of laxative(s) may need to be reduced and subsequently adjusted according to need as fentanyl is less constipating than morphine.