Chin Med J (Taipei) 1998;61:S133.

When Morphine is Not Enough

Dr. Robert Dunlop

Medical Director, St Christopher's Hospice, U.K.

Abstract

Morphine is the most widely used strong opioid. It has an important role in the management of cancer pain. It also has a limited role in treating breathlessness and diarrhoea. This presentation will focus on the use of morphine as an analgesic. Up to 80% of cancer patients will develop cancer pain. Although the WHO Step-ladder recommends the initial use of simple analgesics followed by a weak opioid, most patients will then require a strong opioid. Morphine is the strong opioid of first choice. It is given regularly, starting at a low dose and then titrating upwards until relief of pain is obtained. This paper is concerned with the management of patients whose pain does not respond to morphine.

The usual reasons why morphine is not enough include:

1.The dose is too low. Many health care professionals and patients fear morphine. Consequently, the dose of morphine is not increased sufficiently. The fear of morphine is based on myths about: using morphine too early will reduce its effectiveness; addiction; respiratory depression; and morphine causing premature death.

2.The pain is only partially morphine responsive. The regular administration of morphine is most useful for constant deep somatic pain (eg bone or soft-tissue pain) or visceral pain (eg liver metastases or pelvic organ involvement). Even with these pain syndromes, morphine is most effective when combined with simple analgesics such as acetaminophen and/or paracetamol. Morphine is less effective for neuropathic pain. This is pain associated with nerve damage eg brachial plexopathy, nerve root involvement with extradural metastases, and lumbosacral plexopathy. The use of antidepressants, anticonvulsants, antiarrhythmics, and NMDA receptor antagonists will be reviewed in the presentation.

Incident pain is the other problem which frequently does not respond to regular morphine. This is pain which occurs when the patient does something, such as walking, weight bearing or turning. Impending or actual bone fractures must be considered because surgical stabilisation is very effective, even for patients with advanced cancer. Other options include short-acting opioids, such as sublingual fentanyl, and nitrous oxide/oxygen mixtures (entonox) for inhalation.

3.Toxicity of morphine. Occasionally, patients will not tolerate sufficiently high doses of morphine because of toxicity such as delerium. This is more common with the elderly. Alternative opioids will be considered.

4.Suffering. Sometimes, it is not physical pain which causes patients' distress. Anguish and suffering are not relieved by morphine, though escalating doses of morphine may be an important clue. Other strategies will be highlighted for managing this problem.

[Chin Med J (Taipei) 1998;61:S133.]