Palliative care: Opioids for pain

Last updated: Thursday, January 21, 2016

Often patients are initially managed on a regular dose of an ‘immediate-release’ morphine product such as Oramorph every four hours. When pain control is stable, they are then switched to a modified-release version that is given once or twice daily. The initial dose of modified-release morphine can be calculated by adding up the total amount of oral morphine over 24 hours. This includes regular four hourly doses plus any ‘when required’ doses prescribed for breakthrough pain.
For example, a patient, Paul, has required 10mg oral morphine solution every four hours with two 10mg ‘when required’ doses, for a few days. His 24-hour morphine requirement is 80mg.

His starting dose of modified-release morphine would be 40mg every 12 hours or 80mg every 24 hours.
The BNF advises that the first dose of the modified-release preparation can be given with the last dose of the oral solution, or within 4 hours of it. However, in practice there might need to be more of an overlap while the modified release preparation starts to work. Immediate-release morphine should continue to be prescribed ‘when required’ for breakthrough pain. The ‘when required’ dose should be about one-sixth to one-tenth of the total daily dose of modified-release morphine.
For our patient, Paul, on modified-release morphine sulphate 40mg every 12 hours, the ‘when required’ dose of immediate-release morphine would be around 10mg every 4 hours.

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If a patient becomes unable to swallow, a change in route of administration should be considered. Morphine is often the preferred parenteral opioid via e.g. subcutaneous 24-hour syringe drivers. Fentanyl is a useful alternative that can be given as a transdermal patch. Guidance on conversion between oral morphine and other opioids is given in most palliative care resources. Interpret dose conversion factors with care as they are only approximations, and there is a great deal of inter-patient variability.

Anticipation and management of the side effects of analgesics is an important part of optimising therapy. Nausea and vomiting, sedation and constipation are the most common side effects observed in patients taking opioids. However nausea and vomiting are usually transient and improve after 5-7 days. Patients should take long-term laxatives regularly to minimise the risk of constipation.