Researchers found that not all opioids carry the same risk of severe constipation in a large hospital-based study in the UK.
In an analysis of more than 80,000 adult patients treated for noncancer pain, the researchers reported that morphine, oxycodone, fentanyl, and opioid combinations were linked to higher rates of severe constipation, while tramadol was associated with the lowest risk.
Belay Birlie Yimer of the University of Manchester and colleagues used hospital electronic health records from 2009 to 2020 and focused on patients aged 18 and older who received opioids during their hospital stay. Patients with a history of cancer were excluded. Severe constipation was defined by the administration of an enema or suppository.
Among the 80,475 patients included, 8% experienced at least one episode of severe constipation. Codeine and morphine were the most commonly used opioids, followed by oxycodone and fentanyl.
Compared with codeine, morphine was linked to a 59% higher risk of severe constipation. Oxycodone carried a 46% higher risk, fentanyl had a 37% higher risk, and combination opioid therapy had an 85% higher risk. In contrast, tramadol was associated with a 20% lower risk than codeine.
The researchers also assessed how opioid dosage affected risk. Doses were converted into morphine milligram equivalents (MME) to enable comparison. Patients taking more than 50 MME per day faced significantly higher risks. Those who received between 50 and 120 MME per day had nearly double the risk compared with those taking less than 50 MME per day. The risk remained elevated at 120 MME or more per day, though to a lesser extent.
To better reflect real-world prescribing, the investigators used a time-varying model and adjusted risk as patients changed opioids or dosages during their stay.
The researchers also noted that patients who received stronger opioids such as fentanyl or oxycodone were typically older. Most opioids were given orally, though fentanyl and morphine were often delivered intravenously.
By relying on records of administered medications, the study captured real-time exposure and avoided misclassification that is common in prescription-only data. Using enema or suppository administration as an outcome measure allowed for more precise identification of clinically significant constipation.
These findings may support more individualized opioid prescribing, particularly for patients who are at risk of gastrointestinal complications. Understanding the varying risks that are associated with opioid type and dose can help guide safer pain management decisions.
The authors reported no conflicts of interest.
Source: BMC Medicine