Laxative Use with Patient-Controlled Analgesia in the Hospital and Associated Outcomes

From the Division of General Internal Medicine (Dr. Lenz), Division of Biomedical Statistics and Informatics (Mr. Schroeder), and the Division of Hospital Internal Medicine (Ms. Lawson and Dr. Yu), Mayo Clinic, Rochester, MN.

Abstract

• Objective: To describe prophylactic laxative effectiveness and prescribing patterns in patients initiated on intravenous (IV) opioid analgesia.
• Design: Retrospective cohort study.
• Setting and participants: All patients who were on IV narcotics with a patient-controlled pump while admitted to a general medicine service at the Mayo Clinic in Rochester in 2011 and 2012 were identified. Patients were excluded if constipation or diarrhea were diagnosed prior to IV opioid analgesia initiation.
• Measurements: Prophylactic laxatives were defined as laxatives prescribed within 24 hours of IV opioid analgesia initiation to be given even in the absence of constipation. Constipation was recorded when diagnosed during the hospitalization. Severe constipation was defined as constipation resulting in an abdominal CT or X-ray; abdominal distension, pain, or bloating; or if an enema was performed during the hospitalization.
• Results: Of 283 patients, 101 (36%) received prophylactic laxatives and 182 (64%) did not. Constipation occurred in 61 (34%) not on prophylactic laxatives and in 49 (49%) on prophylactic laxatives (P = 0.015). Severe constipation occurred in 23 (13%) not on prophylactic laxatives and in 33 (33%) on prophylactic laxatives (P < 0.001).
• Conclusion: A large percentage of patients are not receiving prophylactic laxatives when receiving IV opioid analgesia in the hospital. Current laxative strategies are not effectively preventing constipation in patients when prescribed.

Key words: constipation; opioids; hospital medicine; patient-controlled analgesia; laxatives.

Opioid-induced constipation (OIC) is defined as a change, when initiating opioid therapy, from baseline bowel habits and defecation patterns that is characterized by any of the following: reduced bowel frequency; development or worsening of straining; a sense of incomplete evacuation; or a patient’s perception of distress related to bowel habits [1]. It is an important side effect to consider when initiating narcotic analgesia. It has been estimated that approximately 3% to 4% of the population is on chronic narcotic pain relievers in the outpatient setting [2,3], and 37% to 81% of these patients will experience constipation [3–9]. Because of the high incidence of constipation, the prophylactic prescription of laxatives with initiation of opioid pain relievers is frequently recommended [10–15]. Furthermore, it has been shown that among patients admitted to the hospital with cancer, there is a lower incidence of constipation amongst those who have received prophylactic laxatives [16]. However, there is no evidence in the literature that prophylactic laxatives improve outcomes in patients on opioid analgesia in the general medicine inpatient setting. Furthermore, studies have illustrated that recommendations for prophylactic laxative use are not reliably followed [3,9].

While the incidence of OIC is well described in the outpatient setting [17,18], there are few studies looking at the incidence of OIC in the hospital setting. It has been shown, however, that occurrence during even a brief hospitalization is possible [4,6]. Acute constipation while hospitalized can theoretically lead to longer hospitalizations, increased pain, and decreased quality of life [6,7,19]. Recent research has focused heavily on the use of novel agents such as peripherally acting mu-opioid receptor antagonists in the treatment of OIC [20–23]. However, the expense of these agents makes them less than ideal in the prophylactic setting. This study will assess the effectiveness and prescribing patterns of prophylactic laxatives in the inpatient general medicine setting over a 2-year period at our institution in patients initiated on patient-controlled analgesia with hydromorphone, morphine, or fentanyl.

Methods

This study was approved by the institutional review board at the Mayo Clinic Rochester. All patients who were initiated on intravenous analgesia with an electronic patient-controlled opioid pump (PCA) while admitted to a general medicine service in 2011 and 2012 were identified. Patients who received PCA therapy were identified through a pharmacy database. Only patients older than 18 years of age were included in the study. PCA therapy was selected for our analysis because PCA therapy is not regularly administered on an outpatient basis. All of these patients, therefore, had a change in their narcotic regimen on admission to the hospital. Patients were excluded from the study if they were on a PCA for less than 24 hours; had a PCA initiated on a service other than a general medicine service; were on a scheduled laxative regimen prior to admission; or carried a diagnosis of bowel obstruction, chronic diarrhea, constipation, or intestinal discontinuity (eg, those with previous diversions or ostomies).

A retrospective review of each patient’s chart was conducted with the assistance of a team of nurse abstractors. Basic demographic data were recorded for each patient. Date of hospital admission and discharge; scheduled laxatives ordered and administered (any dose of sennosides, polyethylene glycol, docusate, bisacodyl, lactulose, or magnesium citrate); abdominal X-rays and abdominal CT scans performed for constipation; and any administration of enemas were recorded. Fiber supplements were not considered laxatives. If a patient was documented to have constipation during their hospitalization this was recorded. Patients were classified as having severe constipation if an abdominal CT or x-ray was performed for the indication of constipation; if abdominal distension, pain, or bloating were documented due to constipation; or if an enema was performed during the hospitalization.

For analysis purposes, patients who started receiving scheduled laxatives (as opposed to laxatives “as needed”)on or before the day of PCA initiation were classified as receiving prophylactic laxatives. Baseline patient characteristics and outcomes were compared using the chi-square test for nominal variables and the rank sum test for continuous variables. In all cases, 2-tailed tests were performed with P values ≤ 0.05 considered statistically significant. A nominal logistic regression model was utilized to assess for independent association of risk factors with the outcome of constipation.