Incidence of constipation associated with long-acting opioid therapy: a comparative study

Opioid therapy plays a key role in the management of chronic pain. Constipation is one of the more frequently occurring adverse effects associated with opioid therapy.

A retrospective cohort design study was conducted to determine the incidence of constipation in chronic pain patients who received three different long-acting opioids (transdermal fentanyl, oxycodone HCl controlled-release [CR], or morphine CR) for malignant or nonmalignant chronic pain. The data source was claims data (January 1996 through March 2001) from a 20% random sample of the California Medicaid (Medi-Cal) database. Claims data were from adult patients with chronic pain (malignant or nonmalignant) who had no prior diagnosis of constipation and no prior usage of long-acting opioids for at least 3 months before the observation period. Patients were followed for at least 3 months after the initiation of opioid therapy. ICD-9 code for diagnosis of constipation was the main outcome variable. Crude rates of constipation, annual incidence density, relative risk, and adjusted odds ratios were compared.

A total of 1,836 patients (601 receiving transdermal fentanyl, 721 receiving oxycodone CR, and 514 receiving morphine CR) were included in the analysis. Crude (unadjusted) rates of constipation were 3.7% for transdermal fentanyl, 6.1% for oxycodone CR, and 5.1% for morphine CR (P > 0.05). Transdermal fentanyl had a lower annual incidence density and risk of constipation than oxycodone CR and morphine CR (P > 0.05). After adjusting for confounding variables, including race and supplemental opioid use, the adjusted risk of constipation was 78% greater in the oxycodone CR group (P = 0.0337) and 44% greater in the morphine CR group (P = 0.2242) than in the transdermal fentanyl group.

In this population, patients receiving transdermal fentanyl had a lower risk of developing constipation compared with those receiving oxycodone CR or morphine CR.