How should GPs move up the 'analgesic ladder' for cancer pain? How can we assess patients' analgesic requirements and where do adjuvants fit in?
First establish what sort of pain it is, either neuropathic (nerve pain): shooting pain or pins and needles; or nociceptive pain: which is anything else. Nociceptive pain can be subclassified into somatic and visceral, but I find that confusing.
· Step 1 For both types of pain start off at step 1 of the WHO ladder with aspirin and paracetamol, but for neuropathic pain add an adjuvant. I would class NSAIDs as adjuvants, along with neuropathic agents.
· Step 2 If there is still pain, go to step 2, but it is important to understand the gradient within stage 2 and not all drugs are equi-analgesic. If you look at analgesic equivalence 60mg of codeine is equivalent to 6mg morphine, so four times daily would equate to 24mg morphine. A maximum dose of tramadol is 400mg in 24 hours, which equates to 80mg morphine.
· Step 3 If a patient is on maximum dose of a step two agent but still has pain, move up to step three, bearing in mind the analgesic equivalence. Titrate with an immediate-release preparation then convert to a slow-release one when pain control is acceptable. I use oral preparations for patients, unless they cannot swallow, say because of carcinoma of the oesophagus. Patches are only useful for patients who have stable analgesic requirements, but they are good for compliance.
What influences your choice of adjuvant?
I use NSAIDs as an adjuvant for bone pain, co-prescribed with a proton pump inhibitor if necessary. For neuropathic pain I use amitriptyline as a first-line, starting at 10mg if the patient is elderly, otherwise I start at 25mg at night. I would increase up to a maximum of 125-150mg if it is effective, unless limited by side-effects.
If the patient cannot tolerate higher doses then I use gabapentin as second-line, but compliance is worse because it must be taken three times daily and the dose may have to be increased as high as 600-900mg tds to relieve symptoms.
Drug Dose Morphine
Co-proxamol 1 tablet 5mg
Co-codamol 30mg/ 3mg
Codeine 30mg/ 3mg/
Dihydrocodeine 30mg/ 3mg/
Tramadol 50mg 10mg