Prophylactic co-prescribing of regular laxatives along with regular opioids is identified as best practice. [1-3]
In palliative care patients there is a limit to the potential for prevention and management of constipation by dietary, lifestyle or preventive strategies, and these should not be solely relied upon. 
Definition and Prevalence
Constipation has been defined as 'the passage of small, hard faeces infrequently and with difficulty'. Individuals vary in the weight they give to the different components of this definition when assessing their own constipation and may introduce other factors, such as pain and discomfort when defecating, flatulence, bloating or a sensation of incomplete evacuation.  Constipation is a frequent complaint in the general community, and more common in palliative care patients. [4-6] Chronic constipation is one of the commonest side effects of all opioids and occurs in 40 – 70 per cent of patients treated for cancer pain with oral morphine.  However other causes of constipation should also be sought and addressed. 
Opioid induced constipation should be considered during the assessment of constipation. Other possible contributing factors include:
- Medications – 5-HT3 antagonists, anticholinergics, iron, some antihypertensives
- Decreased oral intake, dehydration, alterations in diet
- Metabolic abnormalities (eg, hypercalcaemia, uraemia, hypothyroidism, hypokalaemia, diabetes)
- Decreased mobility, weakness, difficulty accessing toilet facilities
- Bowel obstruction
- Neurological disorder or damage, eg, due to spinal cord lesion
- Autonomic neuropathy
- Terminal phase.
Despite the prevalence of constipation in palliative care patients, it is underdiagnosed and undertreated.  Examination of the patient should include a focused rectal examination, including assessment of the pelvic floor and anorectal structures. Abdominal radiology may be needed to exclude obstruction, but is not required to make a diagnosis. 
As well as addressing and modifying any possible causes of constipation, laxatives are usually required. The evidence base supporting the choice of any specific laxative is not strong, either for the general population, [8,9] or specifically in a palliative care population. [1,10] However, general recommendations for prevention and treatment of constipation in palliative care patients have been made based on expert opinion, and these suggest the combination of a stimulant and a softening agent is usually required. 
Rectal interventions may also be necessary when impaction has occurred, when there is a neuropathic cause for the problem, or when there is a myopathy. This needs to be assessed on an individual basis. Treatment of constipation is addressed in more detail in the sub-section on Pharmacological management.
- One of the difficulties in researching constipation is the lack of a consensus definition.  The EAPC definition relies on the patient’s own subjective assessment of whether or not they are constipated, rather than on frequency of defecation.  There are considerable differences between individuals, which make it difficult to propose a general description of normal and abnormal bowel habits.  As a result, research on the prevalence of constipation and on the outcomes of treatment is difficult to interpret.
- Clinical studies of new drugs for the management of opioid induced bowel dysfunction are ongoing. Several novel opioid antagonists which have only local effects on the gastrointestinal tract, including methylnaltrexone, have shown promise in clinical trials. [11-13] Methylnaltrexone may have additional benefits in improving gastric emptying, however further research is needed. [14,15]
- Other newer potential pharmacological approaches to managing chronic constipation include selective calcium channel agonists (lubiprostone) or 5HT3 serotonin receptor agonists (tegaserod). These agents are not available in Australia and have not yet been studied in the palliative care population. 
- A relationship between deteriorating performance status, opioids, anticholinergic load, proximity of death, and the prescription of laxatives has been suggested.