When "I can't poop" is a result of medication-induced constipation (MIC), it is not just the bloating, sluggishness, stress, and discomfort of constipation that is concerning. Medication-induced constipation can lead to serious health problems such as fecal impaction, bowel obstruction, or bowel rupture, and constantly straining at stool (Valsalva maneuver) can cause an irregular heartbeat or arrhythmia. In addition, patients' efforts to relieve the constipation can lead to inappropriate use of cathartics, overuse of enemas, or dangerous purging. Unresolved MIC often leads to discontinuing necessary medications and "I can't poop" then becomes "I won't take the medicine I need because when I do I can't poop." Moreover, since discussing constipation and bowel habits can be embarrassing subjects for some patients, these complaints may not be communicated to their healthcare provider until a crisis situation develops.
When knowledgeable nurses educate patients about the potential for constipation, they reduce the potential for serious, possibly life-threatening challenges. And, while teaching patients about constipation prevention strategies may avoid the problem of MIC entirely, explaining that treatment approaches are available if MIC develops will encourage communication with their clinician in a timely manner.
In the following paragraphs, the discussion will briefly address constipation and then review examples of mediation that can induce constipation. Strategies for preventing or treating MIC will include both nonpharmacological and pharmacological approaches.
Constipation and the Digestive System
Although one person may experience constipation somewhat differently than the next person, there are commonalities that usually include difficulty having a bowel movement (BM; e.g., having to strain at stool, stools that are lumpy or hard, feeling like evacuation is not complete, having to use manual means to help defecation) or having less BMs than normal for that person. Normal for an individual may be one BM a day, for others, it may be three times a day, and for some, it is one every second or third day. Clinical definitions of constipation usually specify having less than three stools per week (Kumar, Barker, & Emmanuel, 2014).
Constipation, however it is defined, is not a disease. Rather, it is a symptom of a digestive tract not working at optimum. Short bouts of constipation are not at all unusual. Many people experience short-term constipation with diet changes, stress, and travel or lifestyle changes. This is fairly common and these episodes of primary constipation are most often very short, self-limiting, or easily remedied. And, while distinctly uncomfortable, they are not usually dangerous or life-threatening. Constipation that lasts longer and is unresolved can, however, be very serious and in some instances even life-threatening (e.g., ruptured bowel). Medication-induced constipation is one such long-term threat.
Medication-induced constipation is a secondary type of constipation in that the medication used to treat or cure one condition can also induce constipation: The action at the target organ is the desired action whereas the action in the gastrointestinal (GI) tract is undesirable-for example, constipation. The potential for MIC can also be increased if more than one constipation causing medication is used or larger doses become necessary.
The medications that cause constipation all act in some manner that adversely affect normal GI functioning. With optimal functioning, food and water are propelled through the entire system by involuntary continuous rhythmic smooth muscle contractions (peristalsis). In the stomach, such contractions mix food and liquid with enzymes, hormones, and digestives juices produced in the stomach. This liquid mixture, called chyme, is then passed directly into the intestines. Digestion continues along the entire 20+ ft. length of the small intestine. Nutrients are absorbed whereas food waste and liquid are propelled along into the large intestine (colon) where liquid is absorbed and semisoft stool is formed and then pushed into the rectum. As stool collects in the rectum, the nerves then trigger the urge to defecate (U.S. National Library of Medicine, 2017).
Most MIC is caused by either slowing or interrupting the normal rhythmic muscle contractions that propel transit through the intestines and/or by altering the fluid balance in the intestines. In the following section, examples of medication that can cause constipation are discussed. Not every single medication than can cause constipation is identified. However, these examples will help understand the strategies used to prevent or treat MIC.
Medication That May Cause Constipation
Opioid-induced constipation (OIC) is the best known, most frequently experienced, and most difficult-to-treat example of MIC: 50%-95% of patients using opioids for pain relief will experience OIC, and this effect does not diminish with continued use (Kumar et al., 2014). It will begin with the first dose of opioid and continue until the opioid is discontinued. Opioid analgesics exert their analgesic effect by attaching to [mu] receptors in the brain, but there is also a significant number of [mu] receptors in the large intestine and when opioids interact with the [mu] receptors in the large intestine, peristaltic action is directly slowed. This delays propulsion of the fecal material and allows longer time for more absorption of water in the large intestine. The result is drier, harder stool that is more difficult to move.
Some anticholinergics may cause MIC through action at muscarinic receptors in the GI system. Gastric emptying may be delayed and motility through the small intestine is slowed. Slower movement allows for increased water absorption all along the small intestine with drier waste and slower movement of waste into the large intestine (Katzung & Trevor, 2012).
Calcium channel blockers (CCBs) are another class of medications that may induce MIC. Calcium is necessary for any smooth muscle contraction and CCBs are used to successfully treat conditions such as angina or hypertension by decreasing the speed and strength of muscle contraction in cardiac muscle and vascular smooth muscle. Calcium channel blockers may also impact the GI smooth muscle and result in decreased rate and strength of muscle contraction (decreased effect of peristalsis) so that not only is waste moved slower allowing for drier waste but the strength of moving that waste forward is also diminished (Katzung & Trevor, 2012).
Many other medications can lead to MIC. Central nervous system (CNS) drugs such as anticonvulsants and antidepressants may slow GI motility through messaging from the CNS. Diuretics (especially in high doses) may deplete fluid balance in the intestines. The intestinal tract functions a fluid exchange and as fluid is pulled from the rest of the body with diuretics, fluid is then absorbed from the GI tract leaving contents drier and harder to move. Some antacids that contain aluminum and calcium may also cause constipation (National Institute of Diabetes and Digestive and Kidney Diseases, 2017).
None of the medications that have the potential to cause constipation, not even opioids, affect everyone the same. Medication-induced constipation is often an individual response that depends on variables such as general health condition, other medications, activity level, lifestyle, and bowel history (some patients will have a history of frequent bouts of constipation and others may have never experienced constipation). Thus, when teaching about a medication and constipation, the prevention program may need to be tailored for the individual.
Nonpharmacological Prevention
Preventing MIC (including OIC) always begins with a nonpharmacological constipation prevention regimen that includes diet, fluid, and exercise recommendations and planning a regular bowel regimen. Each institution or professional may have its own version of a constipation prevention program; however, most will include the following:
* Include plenty of high-fiber foods in your diet, including beans, vegetables, fruits, whole grain cereals, and bran (helps retain water and move stool through the system).
* Drink 6-8 glasses of water a day (talk to provider if on fluid restrictions).
* Stay as active as possible and get regular exercise (including 15-20 minutes after meals).
* Do not ignore the urge to pass stool (allows for increased water absorption and drier stool).
* Create a regular schedule for BMs.
* Contact your prescriber if you do not have a BM for 4 days or longer, or if you develop diarrhea (diarrhea may indicate a bowel obstruction with leaking around the impaction).
When nonopioids are involved, increasing fiber, fluids, and exercise along with a good bowel retraining program will often prevent constipation. When prevention is not successful and a patient complains about "I can't poop," then the judicious use of a laxative may be necessary until the body adjusts to the constipation-causing medication.
It is vital, however, before any laxative is added to an MIC prevention program, to ascertain that there is no bowel obstruction (impaction) present or, if present, the impaction should be removed before administering any laxative. Using a laxative in the presence of a bowel obstruction will not clear the obstruction but may instead increase the obstruction and add to the potential for very serious damage.
Laxatives
There are several classes of laxatives that vary in way they act at different areas of the intestinal tract, and when a laxative is prescribed, it will usually be prescribed according to the desired action. See Table 1 for examples of brand names and action of available over-the-counter oral laxatives that may be prescribed as part of a treatment program for MIC.
When use of a laxative is prescribed as part of the MIC treatment, patient education is vital to avoid additional problems. Many people in the general population have used an over-the-counter (OTC) laxative at one time or another for a brief bout of constipation. But MIC is different and is not as readily resolved. Thus, a very important aspect of MIC education is stressing the importance of reading the package inserts for any OTC laxative and specifically warning patients about the dangers of overdosing and/or extended use of laxatives. Overuse of laxatives that decrease the transit time through the intestines can result in incomplete absorption of vital electrolytes and necessary medications. Constant stimulation of the GI tract with stimulant laxatives may lead to irritable bowel syndrome, and prolonged use of any type of laxative can result in a flaccid colon that then actually increases constipation.
Generally, the many available OTC laxatives are safe when used appropriately and as part of a MIC treatment program and may resolve the challenge of nonopioid MIC. Treating OIC is often a much more challenging problem.
Treating OIC
Although opioid analgesics cause an analgesic effect by action at opioid [mu] receptors in the CNS, they also stimulate the [mu] opioid receptors in the GI tract. Stimulation of the GI tract leads to inhibition of intestinal mobility, delays in transit time, and decreases of secretion of electrolytes and water into the intestine. This leads to OIC which, unlike other forms of MIC, does not respond reliably to lifestyle changes or treatment with conventional laxatives. In fact, even when lifestyle changes and laxatives are included with opioid treatment, more than 50% of patients develop OIC and the effects are not related to dose and do not diminish with continued use (Wald, 2016). As a result, OIC can be a limiting factor in opioid therapy and result in inadequate pain control, especially for those who have long-term chronic or acute pain that is responsive only to opioid analgesia (Bell, Annunziata, & Leslie, 2009).
There is, however, a new class of pharmacological agents that offers another approach to OIC: the peripherally acting [mu] opioid receptor antagonists (PAMORAs). These agents are not laxatives. Rather, they are [mu] opioid antagonists that have been modified so that they do not cross the blood-brain barrier. The antagonistic action is, therefore, limited to [mu] opioid receptors in the periphery while not compromising the CNS-modified analgesic effect or causing opioid withdrawal symptoms.
Selected PAMORAs approved by the U.S. Food and Drug Administration to treat OIC are identified in Table 2. Although there are similarities in contraindications and cautions among the PAMORAs, these agents are not interchangeable: each has been approved for specific patient populations, each has a different dosing regimen, and each has different drug/drug interaction profile. See Table 2 later.
A PAMORA offers an alternative treatment that will allow patients with intractable moderate or severe noncancerous pain to live a more fulfilling life. Patients should, however, be fully educated about the possible side effects (stomach pain and discomfort) and instructed when to contact their provider with symptoms of possible opioid withdrawal or bowel obstruction
Conclusion
Constipation is usually something many people experience for a short time due to lifestyle changes, diet changes, or stress, and constipation is resolved fairly quickly. But with MIC, the constipation often does not resolve as readily. If the constipation continues, people who do not realize that their constipation is related to a medication will resort to overuse of laxatives or enemas, which can be just as dangerous as prolonged constipation. For individuals who do recognize that their prolonged constipation is related to a medication, they may just discontinue the medication.
Knowledgeable nurses who educate patients about their medications have an exceptional opportunity to prevent most of these life-threatening situations. Nurses not only teach patients about the possibility of MIC and the safe approaches to prevent or treat MIC but also encourage patients to openly and frankly communicate any bowel problems. When patients are informed, then "I can't Poop" will become a trigger to evaluate the current treatment plan rather than having to resolve a major healthcare crisis.
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