Opioid prescribing
Morphine remains the first line oral opioid of choice.
· If regular weak opioid is not controlling pain, initiate sustained release morphine (MST) 10-15mg bd
· At the same time prescribe ‘as required’ oral morphine sulphate solution (immediate release morphine) 2.5-5mg
· Review after 24-48 hours, add up total daily dose of morphine given. Divide by two and prescribe this
new dose as MST (sustained release morphine) twice daily
· At the same time increase dose of immediate release oral morphine solution to one sixth of the total daily dose
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Example: Patient commenced 2 days ago on MST 15mg bd. Over previous 24 hours he has used 6 extra doses of morphine sulphate solution 5mg for breakthrough pain Total morphine dose in 24 hours = 15mg MST+ 15mg MST + (6X 5mg morphine sulphate solution) = 60mg
New dose MST is 60mg divided by 2 = 30mg bd New dose morphine sulphate solution is 60mg divided by 6 = 10mg |
· At the same time initiate regular softener-stimulant laxative (e.g. codanthramer capsules or solution at night )
· If nausea develops as a result of commencing morphine use regular haloperidol 1.5 mg od orally or sub-cutaneously. You may be able to stop this after 5 days.
· Pain needs ongoing review.
· Opioid dosage may need increasing by a third if patient is continuing to experience pain and the pain is opioid sensitive.
· Alternatively summate doses required for breakthrough pain and increase the regular dose accordingly as described previously.
· Laxatives may need to be increased with the increased morphine dose
· Increased drowsiness and pin point pupils may be an indication that the dose of opioid is too high and requires reduction
Oxycodone is the second line oral opioid of choice.
· A small proportion of patients are intolerant to morphine i.e. if they experience profound drowsiness or cognitive side effects. In these situations alternative opioids can be considered.
· The preferred second line opioid is oxycodone.
· Oxycontin is the 12 hourly sustained release formulation, oxynorm is the immediate release preparation
Transdermal fentanyl may be appropriate for certain circumstances
· Fentanyl patches can be useful if patient’s pain is well controlled with morphine and patients are struggling to swallow or there are problems with compliance. However, uncontrolled pain is difficult to manage with fentanyl due to its long half life.
· Care is needed with potency, fentanyl 25mcg/hr is equivalent to 60-90mg morphine/24hrs. Toxicity can occur and a reservoir of fentanyl accumulates under the skin so that significant blood levels can persist for 24 hours after removal of the patch.
Approximate relative potencies of oral morphine, oral oxycodone, transdermal fentanyl and subcutaneous diamorphine
|
4 hrly oral morphine (mg) |
24 hrly oral morphine (mg) |
24 hrly oral oxycodone (mg) |
Fentanyl Patch (mcg/hr) |
24 hrly SC diamorphine (mg) or 24 hrly SC oxycodone (mg) |
|
10-20
|
60-120 |
30 - 60 |
25 |
20-40 |
|
25-35
|
150-210 |
75 - 105 |
50 |
50-70 |
|
40-50
|
240-300 |
120 - 150 |
75 |
80-100 |
|
55-65
|
330-390 |
165 - 195 |
100 |
110-130 |
To convert oral morphine to SC diamorphine
· 3 mg oral morphine equivalent to l mg diamorphine SC
· Prescribe additional single doses of SC diamorphine ‘as required’ for breakthrough pain, equivalent to one-sixth of 24 hr syringe pump dose
If diamorphine is not available:
Oxycodone can be used – the dose is the same as that for diamorphine
Morphine can be used – the dose in the syringe driver over 24 hours is half the oral dose over 24 hours.
If not nauseated on regular oral opioids an antiemetic is unnecessary when converting to SC infusion