Opioid Induced Constipation

Heidi Trautwein CGP,PharmD, RPh, ICP, Inc.

With pain now being monitored as frequently as vital signs, and regulatory standards placing focus on pain management, prescriptions for opioid analgesics increased 700% from 1997-2007. Opioid’s are often the only option for pain management for some patients, however they do not come without adverse effects. Major reasons for discontinuing opioids are gastrointestinal effects such as nausea, vomiting, and constipation, in addition to CNS effects. Because opioid receptors are widely distributed throughout the body, they have a broad range of effects. Factors such as age, gender, and race can contribute to adverse effects of opioid analgesics. The GI tract is dense with receptors that opioid analgesics target, and patients rarely become tolerant of this adverse effect making it the most debilitating and common adverse effect occurring in 45%-95% of patients. Activation of these GI receptors inhibits gastric emptying, reduces mucosal secretions, and increases fluid reabsorption.  These conditions result in hardened and dry stool and consequently constipation.  Prevention is the key to opioid constipation treatment.
Nonpharmacologic approaches to opioid constipation:
The risk of constipation can be reduced by increasing fluid and fiber intake, increasing physical activity if possible, and establishing a regular toileting routine. Caution should be taken when increasing fiber however, because too much fiber with inadequate fluids can exacerbate constipation and lead to an obstruction.
Stimulant laxatives:
Stimulant laxatives are the most common type of laxative used to treat opioid induced constipation. These agents work by triggering intestinal-wall muscles to tighten, squeezing the stool allowing it to pass easily. 
Stool softener:
Stool softeners reduce surface tension of the oil-water interface of the stool. This enhanced incorporation of water and fat results in softened stools, and ease of passing stool.  Use of stool softeners alone is not often effective in treating opioid induced constipation, therefore the use of a scheduled stimulant with a stool softener is usually recommended.
In summary, Opioids are a frequently prescribed medication effective for pain management. The most common adverse effect is constipation, which can be quite severe. Non-pharmacologic interventions should be taken upon initiation of the medication especially increasing fluid intake. Stimulant laxatives in addition to a stool softener are the most effective means of treating opioid induced constipation and should be initiated as soon as constipation becomes evident if not at the initiation of the prescription.

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