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Constipation

    continued...

    Narrowing of colon lumen

    • Related to scarring from radiation therapy, surgical anastomosis, or compression from growth of extrinsic tumor.

    *Frequently seen in oncology patients.

    Constipation is frequently the result of autonomic neuropathy caused by the vinca alkaloids, taxanes, and thalidomide. Other drugs such as opioid analgesics or anticholinergics (antidepressants and antihistamines) may lead to constipation by causing decreased sensitivity to the defecation reflexes and decreased gut motility. Since constipation is common with the use of opioids, a bowel regimen should be initiated at the time opioids are prescribed and continued for as long as the patient takes opioids. Opioids produce varying degrees of constipation, suggesting a dose-related phenomenon. One study suggests that clinicians should not base laxative prescribing on the opioid dose, but rather should titrate the laxative according to bowel function. Lower doses of opioids or weaker opioids, such as codeine, are just as likely to cause constipation.[2] (Refer to the Side Effects of Opioids section in the PDQ summary on Pain for more information.)

    Other diseases, such as diabetes (with autonomic neuropathy) and hypothyroidism, may cause constipation. Metabolic disorders, such as hypokalemia and hypercalcemia, also predispose cancer patients to developing constipation. Once these disorders are corrected, constipation should subside.[1]

    Assessment of Constipation

    A normal bowel pattern is having at least three stools per week and no more than three per day; however, these criteria may be inappropriate for cancer patients.[1,3] Constipation should be viewed as a subjective symptom involving the complaints of decreased frequency with incomplete passage of dry, hard stool. A thorough history of the patient's bowel pattern, dietary changes, and medications, along with a physical examination, can identify possible causes of constipation. The evaluation should also include assessment of associated symptoms such as distention, flatus, cramping, or rectal fullness. A digital rectal examination should always be done to rule out fecal impaction at the level of the rectum. A test for occult blood will be helpful in determining a possible intraluminal lesion. A thorough examination of the gastrointestinal tract is necessary if cancer is suspected.[4]

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