Opioid-Induced Constipation Is Not Adequately Reported by Chronic Non-Cancer Pain Patients

Preliminary data from a scientific poster presented at the American Academy of Pain Medicine (AAPM) Annual Meeting, held March 6-9, 2014, in Phoenix, AZ, revealed a significantly higher incidence of opioid-induced constipation (OIC) among patients taking opioid analgesics for chronic non-cancer pain than self-reported constipation complaints suggest.

Recognizing the estimated rate of OIC occurrence currently varies between 15-90%, a team of pain management researchers from the Advocate Illinois Masonic Medical Center in Chicago, IL, set out to “compare the prevalence of OIC using self-assessment of constipation in patients having chronic non-cancer pain and taking opioid or non-opioid medications, and then compare the incidence with the prevalence in the general population.”

To accomplish that feat, the poster authors performed a cross-sectional analysis on 1,748 subjects classified into one of 3 study groups: chronic pain patients who were taking opioids for at least 30 days (n= 608), subjects who were regularly taking non-opioid pain medications for chronic non-cancer pain (n= 568), and members of the general population who were not taking any pain medication regularly (n= 572). Across all 3 groups, the investigators evaluated demographic characteristics, amount of spontaneous bowel movements per week, use of laxatives, and constipation symptoms self-reported by the patients. Among the 2 chronic pain patient groups, the researchers also assessed pain type, pain medication dose and category, and morphine equivalents for patients taking opioids.

Although there were no differences in gender, age, race, or pain type among the groups, the poster authors found roughly 24% of those taking opioids had constipation defined as no more than 3 spontaneous bowel movements per week, compared to 11.3% of those taking non-opioid medications and 9.4% of the general population — a “highly statistically significant” variance in constipation prevalence. Another statistically significant difference was discovered in the patients’ self-assessment of constipation symptoms, as those receiving opioids had “more severe sensation of incomplete evacuation after bowel movements, straining during bowel movements, pain in the abdomen, and painful bowel movements” than those using non-opioid medications or not using any pain medications regularly.

Turning their focus to the opioid group alone, the poster authors found patients who experienced constipation used double the amount of opioids than those who had regular bowel movements, which resulted in a “negative correlation between the number of bowel movements and dose of opioids (by) morphine equivalents.” Despite that finding, a review of the patients’ medical charts showed only 39% of those with OIC had self-reported their constipation problems in the study. As a result, the researchers were required to “spend more time and more effort asking specific questions to these patients.”

Taking those study outcomes into account, the poster authors concluded their preliminary research “showed a much higher prevalence of OIC in patients using opioid medication for the treatment of chronic non-cancer pain than what is self-reported.”

In terms of the efficacy of standard laxatives in OIC, the results showed >80% of subjects in the non-opioid and general population groups experienced significant improvement in constipation following their use of fibers, bulking agents, stool softeners, and stimulants, but only 40% of the opioid group reported similar response to those laxatives — a finding the investigators said “indicat(es) the necessity for newer agents such as opioid antagonists to treat OIC.”