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Cancer Pain and Strategies to Control it
The symptom most feared by cancer patients is pain, although only about three quarters suffer significant pain throughout the course of their illness. Patients that do experience pain often find that it is related to associated problems such as rapid weight loss or pressure sores and that it isn’t actually due to the cancer itself. The principles of pain relief are careful assessment and diagnosis of the cause of the pain, use of analgesics according to the pain ladder and regular review of the effectiveness of prescribed drugs.
Figure 1 on the left (taken from Kumar & Clark, 2005) shows how cancer pain is managed depending on its severity, the first stage of which uses the pain ladder.
The Pain Ladder
The cancer pain relief programme of the World Health Organisation (WHO) groups drugs into three main classes:
- Non-opioid drugs such as paracetamol or aspirin and other non-steroidal anti-inflammatory medications.
- Weak opioid drugs such as codeine, dextropropoxyphene, and combinations of codeine with paracetamol.
- Strong opioid drugs such as morphine and diamorphine.
The pain ladder states that if optimal use of a drug from the non-opioid class, for example 1000mg of paracetamol given orally every 6 hours, does not provide the patient with satisfactory pain relief then the prescription should be increased by one step to a weak opioid drug. Similarly if the equivalent of 60mg codeine given every 4 hours is still not sufficient to control the patient’s pain then they will require the use of a strong opioid.
Strong Opioid Drugs
Most cancer sufferers progress to the point of requiring strong opioid drugs as their disease becomes more advanced. Morphine is more often than not the drug of choice and should be given orally. The dose has to be individually tailored to the patient’s needs and a good starting point is 10mg every 4 hours or 5mg if the patient is particularly frail or elderly. Occasionally a 10mg dose does relieve a patient’s pain however the effect doesn’t last for the entire 4 hours and in these cases the dose can be increased until satisfactory pain control is achieved.
In some cases a patient may not be able to take oral medication, either because of nausea and vomiting, gastrointestinal obstruction or because of altering levels of consciousness and in these cases the opioid drug needs to be given rectally or parenterally (by injection). For cancer patients who require long term drug administration, continuous subcutaneous infusion is the preferred route and in this situation the opioid drug diamorphine is used because it has greater solubility than morphine. When used subcutaneously or intra-muscularly diamorphine is approximately twice as potent as oral morphine and so is the choice for very advanced cases of cancer.
Side Effects of Opioid Drugs
Opioid drugs have a number of side effects when used on a long term basis including the following:
- Constipation – constipation is caused by many analgesic drugs and especially by morphine. A prescription of stimulant laxative to be taken at night is very often administered at the same time as morphine is started. No tolerance develops to this particular side effect and so laxatives have to be continued for as long as pain relief is prescribed.
- Nausea or vomiting – this occurs in around half of the cancer patients that are prescribed morphine. However for patients who have worked their way through the pain ladder and have no other cause for vomiting then an antiemetic used as required is usually sufficient to combat vomiting. In addition, tolerance normally develops within 4-5 days of starting morphine use.
- Confusion, nightmares and hallucinations – these psychological problems occur in a small percentage of patients and tolerance does not develop over time. Therefore this side effect usually requires a change of opioid drug.
Unfortunately not all cancer pains are relieved by opioid drugs by themselves however the addition of co-analgesic drugs often result in improved pain control. For example, non-steroidal anti-inflammatory drugs can be used in addition to weak or strong opioids for bone pain while some steroids have been found to help relieve the pain associated with nerve destruction. In addition to drugs many other techniques such as radiotherapy, anaesthetic and neurosurgical intervention are also employed for the treatment of specific cancer related pains.
Pain is a complex experience unique to an individual and its method of
control must be regularly reviewed so that optimal control is achieved.
Unfortunately as patients climb the pain ladder from non-opioid drugs
to weak and then strong opioids it is very uncommon for them to descend
back down and so everything should be done to make optimal use of the
lowest level drugs possible. Late stage cancer and pain go hand in hand
however with the development of more potent analgesics the experience
of pain can easily be controlled so that patients can carry on living
life for as long as possible.
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