Medication-induced constipation: Clinical sciences

Medication-induced constipation refers to a decreased stooling frequency or difficulty passing stool due to medication side effects, most commonly opioids.

Opioids are medications that can bind mu receptors in the central nervous system, and provide analgesic effects, but they can also affect the gastrointestinal tract, eventually decreasing gastrointestinal motility. In severe cases, this can result in constipation.

Other important non-opioid medications that may cause constipation include anticholinergics, antidepressants, antispasmodics, and calcium channel blockers.

DMT_1 Now, if a patient presents with signs and symptoms suggestive of medication-induced constipation, you should first perform a focused history and physical examination.

Your patient might report decreased stooling, such as two or fewer bowel movements per week; as well as difficulty passing stools; firm stool consistency; or a sense of incomplete stool evacuation after defecation.

Additionally, history might reveal the use of medications like opioids, or non-opioid medications like anticholinergics, antidepressants, antispasmodics, or calcium channel blockers.

On physical examination, you’ll typically find mild to moderate abdominal distension, while rectal exam may reveal fecal impaction, hemorrhoids, anal fissures, or even rectal prolapse. Based on these findings, you should suspect medication-induced constipation.

Now here’s a clinical pearl to keep in mind! Whenever a patient presents with signs and symptoms of constipation, you’ll first need to rule out medical causes, like dehydration or hypothyroidism. Look for red-flag symptoms, like a history of unintentional weight loss or blood in the stool, as well as physical exam findings like significant abdominal distension or tenderness.

If any of these are present, evaluate for other causes of constipation, such as colon cancer or bowel obstruction.

DMT_ 2 Now, once you suspect medication-induced constipation, review your patient’s medication list to identify the cause. If they have been taking an opioid for 7 or more days, and if constipation began or worsened after initiating the medication, you can diagnose opioid-induced constipation, or OIC for short.

Next, you should review the specific opioid and dose, and consider medication changes. This might include reducing the opioid to the minimum effective dose; as well as opioid rotation or switching to a different opioid agent; or even switching to a non-opioid medication.

Next, encourage lifestyle modifications, like educating the patient to defecate immediately upon urge, optimizing dietary fiber and fluid intake, and increasing physical activity. In addition, start medical management with a scheduled combination of laxatives. For example, combine a stimulant laxative, such as senna and bisacodyl, with an osmotic laxative, like polyethylene glycol, which is more effective than either medication alone.

Now, here’s another clinical pearl!  When you prescribe opioids to a patient, keep in mind that your patient will be at increased risk for OIC, so prophylactically prescribe a laxative with or without a stool softener, and educate your patient on lifestyle modifications.

Now that you’ve initiated the management, assess your patient’s response to treatment.

If your patient has an adequate response to treatment and their constipation improves, then continue current management.

On the other hand, if there’s inadequate response and their constipation persists, prescribe a peripherally-acting mu-opioid receptor antagonist, or PAMORA, such as naldemedine, naloxegol, or methylnaltrexone.

PAMORA medications block the activity of mu-opioid receptors in the intestines but not in the CNS, reducing the constipating effect of opioid medications without reducing their analgesic effects.

After one week, reassess your patient’s response to the prescribed PAMORA, and if constipation improves, continue current management.