Pain management

Question 1

What is the conversion ratio of oral to subcut morphine?

Answer 1

Approximatley 2:1

Example

• Morphine 5mg sub cut x6 per day = morphine 30mg sub cut per day
• Approx. morphine 60mg orally per day

Question 2

What is the conversion ratio of dihydrocodeine to morphine?

Answer 2

Approximately 10:1

Example

• Dihydrocodeine 60mg 4x day = dihydrocodeine 240mg per day
• Equivalent to 24mg morphine

Question 3

How is morphine metabolised?

Answer 3

Morphine is metabolised in the liver by glucuronidation to morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G). M3G is probably inactive. M6G has analgesic properties but is also responsible for the toxicity.

Question 4

Where are morphine metabolites excreted?

Answer 4

Kidney

Question 5

What are clinical features of opiate toxicity?

Answer 5

• Altered consciousness
• Confusion
• Vivid dreams
• Pseudohallucinations/hallucinations
• Myoclonus
• Hyperalgesia and whole body allodynia.

Question 6

What are pseudohallucinations?

Answer 6

Disorders of perception that resolve when attention is brought to bear e.g. thinking there is a person in the bedroom with you but then realising it is just the dressing-gown hanging on the door

Question 7

What is myoclonus?

Answer 7

Muscle twitching - a sign of neuromuscular hyperexcitability. Usually more evident when the patient is relaxing.

Question 8

What is hyperalgesia?

Answer 8

Severe pain experienced from a mildly painful stimulus

Question 9

What is allodynia?

Answer 9

Pain experienced with non painful stimulus. Even light touch of the skin can be intolerable. Nurses may report this as they struggle to provide the patient with personal care.