Approximately 70% of cancer patients experience pain, as do many of those with non-malignant disease. Understanding the nature of the pain is critical in controlling it. Pain that arises from tissue damage (nociceptive pain) usually responds to simple analgesia and opioids. By contrast, pain from nerve compression, infiltration or destruction is often resistant to opioids.
Persistent pain requires regular analgesia. Paracetamol, aspirin and non-steroidal anti-inflammatory drugs (NSAIDs) should be considered initially, unless the pain is severe on presentation. NSAIDs should be used with caution in older people, particularly as renal impairment, cardiovascular disease, gastric symptoms and hypertension are common. If there are no absolute contraindications, short courses of NSAIDs can be used to reduce pain to a point where regular paracetamol will control it.
Opioid analgesia
While there is community concern about the use of opioid analgesia, it should not be withheld from people with ongoing, poorly controlled pain. Very low-dose opioids can provide excellent analgesia in frail older people with conditions like chronic osteoarthritic and spinal pain. Drugs such as buprenorphine patches and low-dose sustained-release oxycodone provide analgesia with low exposure to opioids. Co-existing conditions like renal impairment should be considered when dosing opioids, and vigilance to identify potential toxicity is essential.
There is a wide range of opioids available. It is sensible to be familiar with three or four and know their properties well. In particular, it is important to understand the relative potency of the drugs and their route of elimination. The lowest dose of fentanyl patches, for example, is the equivalent of a daily morphine dose of 40 mg. Using it in an opioid-naïve patient is likely to cause significant toxicity. However, fentanyl is entirely excreted by the liver, so is a good choice in severe renal impairment.
While tramadol and tapentadol bind to the mu opioid receptors, and thus are classed as opioids, they also work on noradrenaline and serotonin neurotransmitters, and so have widespread adverse effects including life-threatening serotonin syndrome.
Conversion tables and phone apps that allow rapid calculation of equivalent doses of different opioids are available. Examples include the evi-Q opioid dose calculator,10 the Australian and New Zealand College of Anaesthetists Faculty of Pain Medicine’s Opioid Calculator11 and the GP Pain Help app.12
Adjuvant therapies
The amount of opioid analgesia required can be reduced by using drugs that reduce the intensity of the cause of the pain. For example, antispasmodics (e.g. hyoscine) can reduce the impact of an obstructed hollow viscus, like the gut or the ureter. Oral steroids and NSAIDs can reduce the oedema associated with a hollow viscus obstruction and are widely used in palliative care. Dexamethasone has less propensity to cause adverse effects than prednisolone, but long-term use leads to adverse effects. Infusions of bisphosphonates (e.g. pamidronate or zolendronic acid) can prevent pain from bony secondary tumours and lower the risk of fractures. They are also used to reverse hypercalcaemia.
Neuropathic pain
Neuropathic pain is frequently resistant to simple analgesics and opioids and requires adjuvants. One antiepileptic drug, pregabalin, is approved for neuropathic pain treatment. However, the dose range is enormous. Much of the neuropathic pain in older people will be managed with quite low doses. To minimise the risk of adverse effects, pregabalin should be started at the lowest possible dose of 25 mg twice a day, and slowly titrated upwards over several days. Antidepressants, particularly low-dose tricyclic antidepressants like amitriptyline, are very useful in this situation. Similarly, a slow titration (from a minimum of 10 mg daily to a maximum of 75 mg daily) is essential to minimise adverse effects.9