Drug Management of Cancer Pain
Dr J C D Wells, Liverpool, UK
The relief of pain in cancer should be no mystery to any physician with a passing interest in pain relief. The principles and the drugs that are used have been re-iterated on many occasions. It is, however, interesting to see how fashions have changed over the years.
It must also be remembered, even in cancer pain, that pain is a physical and emotional experience. Evaluation of the causes of pain is absolutely essential if treatment is to be successful. There are often several nociceptive sites of pain which require different medications, and several complicating factors, such as anxiety, depression, fatigue and the like.
The World Health Organisation's analgesic ladder has been modified slightly over the years, and stresses the use of simple anti-inflammatory agents for mild pain in the initial stages, and that these agents should be continued if beneficial or if there is an inflammatory process present. If the pain is not relieved a weak narcotic should be prescribed, such as Codeine or Dihydrocodeine, but recent evidence suggests that these agents work in any case by being metabolized to morphine, and in many cases it is acceptable to commence with an opiate to control pain. There are still licensing difficulties in some countries but in Europe opiates are generally readily available, although sometimes large doses are frowned upon.
The whole object of an opiate is to achieve a steady state blood level for steady state pain. Thus long-acting agents are more useful than short-acting agents. Morphine is the drug of choice, and should be given by the clock, with the dose titrated to achieve adequate pain relief. Whenever possible it should be given by mouth, but suppositories can be given if the patient has difficulty swallowing, or is retching or vomiting. If there is great difficulty in achieving adequate levels by mouth, then a syringe driver can be used with a subcutaneous infiltration.
New and novel agents have come and gone, enjoying phases of popularity. Buccal morphine failed to live up to expectations. Fentanyl patches, however, have become very popular although they are an expensive way to relieve pain in the majority of patients. Neither do they provide much flexibility. They are probably being over-used, although undoubtedly they represent a useful contribution. Opiates can of course be given spinally via drug delivery systems, which will be the subject of a further talk.
Difficult pain syndromes to control include neurogenic pain and interval pain. Neurogenic pain can be managed best by using anticonvulsants for the shooting elements of the pain, and tricyclic antidepressants for the burning element. As with the use of morphine, careful titration of the dose is essential, and the use of a variety of agents can be considered. Peripheral neuropathy may respond to Vitamin B.
Other causes of pain need consideration of appropriate treatment. Steroids can be used for nerve compression, raised intracranial pressure, discomfort from a large tumour mass or soft tissue infiltration. Antibiotics should be given for secondary infection. Diazepam, Baclofen and Clonazepam can be given for muscle spasm and injection of Botulinum toxin should be considered in intransigent cases. Chlorpromazine and local steroid suppositories can be given for the troublesome symptom of tenesmus. Lymphoedema merits treatment with diuretics and a compression sleeve.
Pain due to malignant disease can have many different causes. Successful pain control requires an accurate assessment of the causes followed by appropriate treatment, using analgesics, co-analgesics and sometimes non-drug methods. Approximately 90 per cent of patients can have their pain well controlled by analgesics, with a minimum of side-effects. Others will need to go on to have more complex techniques, but it is essential that the clinician has a full understanding of medication and that these techniques are tried before procedures which carry the possibility of significant and permanent side-effects.
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