Constipation is a very common symptom in patients with advanced disease of any kind, including cancer. Patients at the end of life have many reasons for becoming constipated, including immobility, reduced fluid intake, and the use of a number of medications. Patients frequently need to have bowel movements in inconvenient and unfamiliar places, and in unnatural (non-physiologic) positions. Medications, especially opioids, contribute to constipation. Other medication causes of constipation include tricyclic antidepressants and diuretics, as well as anti-serotonin anti-nauseants, such as ondansetron and granisetron.

Investigating constipation includes paying attention to history, noting typical symptoms, such as anorexia, nausea, vomiting, abdominal pain, bloating, tenesmus and diarrhea (leaking past the fecal obstruction), as well as conducting abdominal and rectal exams. X-rays of the abdomen may be helpful to rule out obstruction. Bloodwork may be needed to rule out hypercalcemia, the most common metabolic cause of constipation in cancer.

Anticipating and preventing constipation, and treating it before it becomes severe, is always preferred. Long-standing constipation is more difficult to manage. Assuming there is no underlying bowel obstruction, treatment includes correcting reversible metabolic abnormalities and identifying offending medications that could be reduced or changed. As much as possible, allow regular bowel movements to occur after meals, in natural (physiologic) positions, in private surroundings.

Bulk-forming laxatives (such as fibre supplements) should usually be discontinued, as they require more fluid intake than many palliative care patients are able to consume. As well, opioids frequently limit intraluminal moisture, which is required for bulk-forming agents to be effective. Docusate is frequently prescribed as stool softener, but there is little evidence that it is effective.

Starting with a stimulant laxative (such as senna), then adding an osmotic laxative (such as lactulose) if needed, has been an accepted approach. More recently, based on evidence, guidelines[1] suggest the use of polyethylene glycol (PEG) marketed as Lax-A-Day, Restoralax and others. PEG can be mixed in a favourite drink or sprinkled on food. PEG may cause less cramping than other laxatives.

If the rectum is full of stool, a low enema may be helpful to get things going. If the stool is hard and impacted, manual disimpaction with extra analgesia before the procedure may be required. Once constipation is resolved, the regular use of laxatives helps to prevent recurrence of this problem.

A special situation results when severe opioid-induced constipation does not respond to the usual agents described above. In this scenario, using subcutaneously injected methylnaltrexone may be helpful.

Reference

1. Librach L, et al. Consensus recommendations for the management of constipation in patients with advanced, progressive illness. J Pain Symptom Manage. 2010;40(5):761-773.

Other references

Fraser Health. Hospice Palliative Care Program Symptom Management Guidelines: Bowel Care. Surrey, BC; 2006.

Winnipeg Regional Health Authority Palliative Care Program. Constipation Assessment and Management Algorithm. Winnipeg, MB; 2012.

Woelk C. The hand that writes the opioid… Can Fam Phys. 2007;53:1015-1017.