Opioid-induced Constipation

Last modified: September 23, 2013 01:04:08 PM

Approximately 41% of patients receiving opioids for moderate-to-severe pain experienced at least one event of constipation

Opioids, a class of pharmaceuticals that are prescribed for pain relief including morphine, codeine, OxyContin, Vicodin and others, have several negative side effects.  One of the more unpleasant of these side effects is constipation.

Constipation is the very infrequent passing of formed stools, or the hardening of stools that are difficult to pass.  There are several factors which can contribute to the onset of constipation, some of which are a lack of fiber, an inadequate intake of liquids, and a lack of exercise.  Constipation can also be caused by a variety of physical conditions and disease.  However, what often gets ignored is the fact that pain-relief medication based on opioids is also a major contributor to constipation.

Opioid medications in general affect the digestive system in a few ways.  First of all, the opioids slow the digestive system right down; stool simply takes much longer to get through.  The medications cause the small intestine to contract in a non-propulsive way, decreasing the longitudinal propulsive peristalsis which pushes food through the digestive tract.  The food ends up staying in one place.  Furthermore, opioids provoke gastroparesis, a partial paralysis of the stomach.  Food also ends up remaining in the stomach for a much longer period of time.  Digestive secretions are decreased with the ingestion of opioids, which means the urge or need to defecate will be greatly reduced.  It is thought that mu-opioid receptors present in the digestive system, spinal cord and brain are involved with causing constipation.

Symptoms of OIC include abdominal tenderness, hard and dry stools, difficulty and pain while defecating, bloating or bulging in the abdominal area, and a constant feeling of needing to use a toilet.  Other symptoms might include feeling tired, depressed, sick and having no appetite.  To treat OIC, physicians at first may simply recommend lifestyle changes such as a high-fiber diet and increasing water intake along with some exercise.  However, this may not work in all cases and may not even be viable for some patients, so other treatment may be necessary.  Most of the time, doctors will prescribe cathartics and/or laxatives at the same time the opioids are prescribed so that the patient will not suffer the distress of constipation.  The laxatives and cathartics will work to speed up the digestive process, increase intestinal motility and soften stool.

At times, oral medication may not work in the treatment of OIC; suppositories, enemas, rectal irrigation and manual evacuation may be necessary.  British doctors found that a combination therapy worked best for the treatment of OIC; medication and lifestyle changes were both beneficial when treating constipation.   However, some critics do say that the medication will not treat the underlying cause of OIC which is opioid receptor-mediated and needs specific, targeted treatment.  One treatment involves the use of methylnaltrexone, a mu-opioid receptor antagonist which counteracts the constipating effects of opioids without decreasing the opioid’s pain relief ability.

If an opioid medication has been prescribed by a doctor to combat pain, it is a patient’s right and duty to ask as many questions as possible in order to be informed and reduce the risk of developing OIC.