Opioids: Switching Between Formulations

Opioids: Switching Between Formulations

For symptom management guidance with opioids, refer to Dyspnoea or Pain.


Calculating equianalgesic doses is a skill that improves with experience. Dose conversion calculators use average equivalent doses of opioids and therefore individuals are likely to respond differently.

Take a conservative approach to equianalgesic opioid dose calculations, review the person frequently and ensure that they have adequate dose available as required for breakthrough symptoms.

Before changing opioids, calculate the total amount of regular and breakthrough opioid taken in the previous 24 hours. Convert this dose to the equivalent morphine dose, then convert to the appropriate opioid dose for the new opioid and route of administration.

When changing from one opioid to another, consider starting the new opioid at 50-75% of the calculated equianalgesic dose. This is to account for individual variation in response. Any supplemental pain relief is managed with breakthrough doses.

For frail and older people, consider using the lower dose (i.e. 50% of the calculated equianalgesic dose).

Useful information

Faculty of Pain Medicine, Australian and New Zealand College of Anaesthetists (FPM ANZCA)

Australian Medicines Handbook (AMH) (Subscription required)

Safe Care Victoria 

eviQ: Cancer Treatments Online - available online only (free login required)

Therapeutic Guidelines: Palliative Care (subscription required)


  • Include 'as required' doses, when calculating the total daily (24-hour) dose.
  • Are the person’s symptoms controlled? Are they experiencing any side effects?
  • As a general rule, 'as needed' doses should be between one sixth and one twelfth of the total daily opioid dose.
  • Equivalent doses between opioids are approximate and can differ greatly between resources.
  • Always monitor the person carefully and regularly if transferred between opioid formulations.

Page last updated 19 September 2019