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You see a 78-year-old lady on the palliative care ward who is suffering from pancreatic cancer with multiple metastases. She has deteriorated over the past week and you feel she is coming to the end of her life. She is unable to swallow medication due to her weakness and you decide to start her on a syringe driver. She currently takes 30 mg MST Continus every 12 hours as well as Oramorph 5 mg every four hours for breakthrough pain.
Which dose of diamorphine would you start in the syringe driver over 24 hours?
10 mg diamorphine
30 mg diamorphine
40 mg diamorphine
60 mg diamorphine
70 mg diamorphine
Key Learning Point
Dose conversion of morphine should be done with care to avoid under- or over-treating a patient.
When converting doses of morphine, initially the total amount of daily morphine should be calculated.
30 mg MST Continus every 12 hours = 60 mg oral morphine/24 hours
5 mg Oramorph every 4 hours = 30 mg oral morphine/24 hours
Total amount of oral morphine = 90 mg/24 hours
The dose conversion for oral morphine to subcutaneous diamorphine is 3:1 so this figure should be divided by 3.
90 mg/3 = 30 mg subcutaneous diamorphine/24hrs.