What are the equivalent doses of oral morphine to other oral opioids when used as analgesics in adult palliative care? How do opioid conversion factors work and what are the key considerations when switching between different opioids?

Opioid Conversion Factors and Considerations

When converting from one opioid to another, healthcare practitioners must consider the relative potency of the two drugs, the route of administration, and the individual patient’s response. Opioid conversion factors are an approximate guide, as comprehensive data is lacking and there can be significant inter-individual variation.

In most cases, the calculated dose-equivalent must be reduced by 25-50% when switching between opioids to ensure safety. An even greater dose reduction of at least 50% is recommended when switching at high doses, in elderly or frail patients, or due to intolerable side effects.

The half-life and time to onset of action of the two opioids must also be considered to avoid breakthrough pain or excessive dosing during the conversion period. Once the conversion has occurred, the new opioid dose should be carefully titrated based on the patient’s individual response, with close monitoring for side effects and efficacy.

Approximate Equi-Analgesic Potencies of Oral Opioids

The following table provides approximate equi-analgesic potencies for common oral opioid analgesics compared to 10mg of oral morphine:

• Codeine phosphate: 0.1 (100mg)
• Dihydrocodeine: 0.1 (100mg)
• Hydromorphone: 5 (2mg)
• Methadone: Relative potency depends on starting dose and duration of administration; conversions to/from methadone require specialist advice
• Morphine: 1 (10mg)
• Oxycodone: 1.5 (6.6mg)
• Tapentadol: 0.4 (25mg)
• Tramadol: 0.1 (100mg)

Transdermal Opioid Conversions

Transdermal opioid formulations, such as buprenorphine and fentanyl patches, can also be converted to oral morphine equivalents:

Buprenorphine Transdermal Patches

• Changed weekly: 5 mcg/hr = 12mg/day oral morphine, 10 mcg/hr = 24mg/day, 20 mcg/hr = 48mg/day
• Changed twice weekly: 35 mcg/hr = 84mg/day, 52 mcg/hr = 126mg/day, 70 mcg/hr = 168mg/day

Fentanyl Transdermal Patches

• 12 mcg/hr = 30mg/day oral morphine, 25 mcg/hr = 60mg/day, 50 mcg/hr = 120mg/day, 75 mcg/hr = 180mg/day, 100 mcg/hr = 240mg/day

Considerations When Switching Opioids

Switching between opioids should only be recommended or supervised by a healthcare practitioner with adequate competence and experience. If uncertain, seek advice from a more experienced practitioner.

Opioid rotation or switching may be considered if a patient obtains pain relief with one opioid but experiences severe adverse effects. When converting between opioids, the goal is to find the optimal balance between pain relief and manageable side effects for the individual patient.

Withdrawal Symptoms

Abrupt discontinuation or significant dose reduction of an opioid can result in withdrawal symptoms such as sweating, yawning, abdominal cramps, restlessness, and anxiety. Careful dose titration and monitoring is essential when switching between opioids to prevent these adverse effects.

Further Reading

• British National Formulary
• Fine PG, Portenoy RK. Establishing “best practices” for opioid rotation: conclusions of an expert panel. Journal of Pain and Symptom Management 2009;38:418-25.
• Twycross R, Wilcock A, Howard P. Palliative Care Formulary (PCF5). 2014.
• UK Medicines Information. Q&A 42.8 What are the equivalent doses of oral morphine to other oral opioids when used as analgesics in adult palliative care? 2016.
• Webster LR, Fine PG. Review and critique of opioid rotation practices and associated risks of toxicity. Pain Medicine 2012;13:562-70.

Key Takeaways

• Opioid conversion factors are an approximate guide due to lack of comprehensive data and individual variation
• Calculated dose-equivalents should typically be reduced by 25-50% when switching between opioids to ensure safety
• Careful consideration of the pharmacokinetics of the two opioids is needed to avoid adverse effects during the conversion period
• Abrupt opioid discontinuation or dose reduction can lead to withdrawal symptoms, requiring gradual dose titration
• Opioid switching should only be undertaken by healthcare practitioners with adequate competence and experience