Alleviating Bowel-Backup in Opioid Induced Constipation

The goal of opioid treatment is to relieve pain and discomfort, but one side effect of the drugs can replace that pain with another problem—opioid induced constipation (OIC). This constipation is more than just a minor inconvenience, says Gregory L. Holmquist, PharmD, CPE, a pain and palliative care specialist. This constipation sometimes becomes so severe that it leads to fecal impaction, which can be life-threatening, according to the National Cancer Institute.1  If untreated, it can lead to colonic necrosis, a dangerous condition that may require surgeons to remove the damaged section of colon, according to Dr. Holmquist. And a significant number of patients taking opioids have constipation even after they take measures to combat it.

Below Dr. Holmquist discusses how to assess patients for OIC, how to prevent the condition and how to manage it.


IDENTIFYING OPIOID INDUCED CONSTIPATION

In a healthy population, the average frequency of bowel movements ranges from three times a day to three times a week. Based on a patient's perspective of what is "normal," he or she may report being constipated, without necessarily meeting the criteria for constipation. How are these patients best managed?

One of the keys to proper treatment is to avoid focusing on the frequency of stools, which can be highly variable among individuals, and instead to ask more detailed questions about stool quality and comfort.

We've done a really good job talking about pain with patients. We need to do the same with regard to the issue of constipation. Ask:

  • What's the consistency?
  • Is it different than in the past?

For example, if a patient is having the same number of stools as he or she typically does, but the stools that are hard as a rock and that the patient is on and off the toilet all day, that indicates a problem. Also, ask if stools have changed over time. If the patient used to have two normal bowel movements twice a week, and now those movements are abnormal in terms of consistency, it can take away from the patient's quality of life. Constipation can lead to hemorrhoids and anal fissures. In some patients, the bowels become the overwhelming focus of their lives. They are taking pain medication to increase comfort, but instead the discomfort shifts elsewhere.

How does OIC differ from other types of constipation?

The mechanism that causes OIC is different from that of traditional constipation for several reasons. First, the medication slows down peristalsis, so solids don't move efficiently through the digestive tract. Opiates also displace fluid inside the bowel, which makes the stool hard. The drugs also dampen the normal defecation response—the urge to "go." Opioids can also affect the secretory glands in the bowel, reducing the amount of natural lubricant inside, causing stool to adhere to the bowel wall. This causes the bowel wall to become rigid, and over time the stool can become impacted.


OIC PREVENTION AND TREATMENT STRATEGIES

What protocols are generally utilized in hospitals for the prevention of OIC? How effective are these strategies?

I think, up until now, we haven't seen much success in preventing or treating OIC. A typical protocol included the use of laxatives, progressing to milk of magnesia and enemas. If these strategies weren't successful, the patient would typically end up with an impacted bowel and need to be disimpacted. This painful and humiliating process can take up to four or five days. Those methods are still often used despite the availability of new opioid antagonists that are very effective in preventing and treating OIC.

Once a patient experiences OIC, what medical strategies and lifestyle changes can be implemented? How have newer treatments, such as the opioid receptor antagonist methylnaltrexone bromide, changed the landscape of OIC management?

One of the most effective treatments for OIC is the use of methylnaltrexone. Unlike a standard opioid antagonist, methylnaltrexone doesn't act on the brain. The drug stays in the bowel, so patients using the drug won't experience withdrawal or increased pain. The agent has been on the market for four years, but because initial studies on the drug were performed in hospice patients, many physicians still reserve it for use in that population.

But methylnaltrexone should be used in conjunction with other strategies, because constipation is multi-factorial. Many patients have risk factors for constipation before they begin taking opioids—the drugs just magnify an existing problem. These risk factors may be related to a poor diet, a lack of exercise or low fluid intake. Taking methylnaltrexone in these cases won't solve problems by itself. The goal of methylnaltrexone is to create an opioid-naive bowel, but the patient may need to add dietary changes and other lifestyle changes to eliminate the constipation.

I believe that methylnaltrexone is very effective with regard to OIC, but it is underused or used too late. Most clinics, hospitals and office practices have not yet put methylnaltrexone as part of an early intervention in their protocols for managing OIC. In talking with a variety of health care providers, the three biggest failures that providers have treating OIC are:

  • waiting too long to use an effective pharmacological intervention such as methylnaltrexone
  • limiting methylnaltrexone's use to hospital settings
  • only giving a single dose of methylnaltrexone instead of using it on a regular proactive basis to manage ongoing OIC

The best way to manage OIC is to be proactive instead of reactive.

Are there patient populations in which methylnaltrexone cannot be used?

So far studies have only identified one group that should not use methylnaltrexone—individuals with mechanical bowel blockages, such as a tumor. In these patients, using methylnaltrexone carries a serious risk of bowel perforation. But other than that group, there have been very few problems with the drug. There are no drug interactions. It won't make dementia or heart palpitations worse. It won't cause renal dysfunction, although doctors might want to reduce the dose for patients with existing renal dysfunction. But overall, the vast majority of patients have no problem using this drug. Methylnaltrexone gives us a specific, targeted pharmacological method to effectively manage OIC in most patients.

REFERENCES

1. National Cancer Institute. Gastrointestinal Complications. Available at: http://www.cancer.gov/cancertopics/pdq/supportivecare/gastrointestinalcomplications/Patient/page2. Accessed on June 8, 2012.

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