BOSTON – Many cancer patients do not pursue or at least do not achieve complete freedom from pain when permitted control over their opioid dose, according to a comprehensive analysis of published studies that evaluated patient-controlled analgesia.
“We do not know why. Patients were encouraged in these studies to titrate opioids until they were pain free or until they had side effects. Although this could be an issue of side effects, another interpretation is that complete pain control is not the goal for many individuals,” reported Dr. Brian H. Wetherington of the University of Kentucky, Lexington.
The data from this analysis were presented at the International Conference on Opioids from a comprehensive literature search that included 905 potentially relevant articles. Of these, 62 met inclusion criteria, particularly an assessment of patient-controlled opioids in patients with cancer pain. The studies also had to assess pain control with a visual analog scale (VAS) or the Neuropathy Pain Scale (NPS) using a 10-point system with 10 being the greatest level of pain imaginable.
“We were interested in evaluating whether patients, when given complete control over their opioids, would take sufficient doses to provide complete pain relief, which is often stated as the goal in pain management,” explained Dr. Wetherington, who was coauthor of a study led by his colleague at University of Kentucky, Dr. Michael Harned.
The answer was no. When the data from the 62 studies, which included 5,251 patients with cancer pain were collated, the average pain score at baseline was 5.4. At the time of assessment of pain control, the mean pain score was 2.7.
“The mean pain score for patients managing their own cancer pain on opioids was reduced from study entry but remained at the moderate to severe pain level or higher than what many health care providers would recommend,” Dr. Wetherington reported.
This review of published studies does not explain why lower pain scores are not reached, but the Dr. Wetherington and his coauthors hypothesized that patients are demonstrating their own benefit-to-risk ratio assessment.
This is thought to be the first systematic review to find that patients do not seek complete control of pain when given access to unrestricted analgesia, but several individual studies have made the same point. In one study cited by the authors, patients on a fentanyl patch only reduced their pain scores to 3.0 on average when given unlimited access to oral morphine for breakthroughs (J. Pain Symptom Manage. 1998;16:102-11).
“We think this deserves further study, because there may be lessons regarding how we think of optimal pain control. While the therapeutic target is often described as complete pain relief, these data suggest that this may not be the goal for patients when they are left to select their own level of pain control,” Dr. Wetherington explained.
The same observation regarding the failure of patients to eliminate all pain on patient-controlled analgesia has been made anecdotally by Dr. William G. Brose of Stanford (Calif.) University. However, he suggested in an interview that patients might be reluctant to rate themselves completely pain free on a subjective scale. He also believes that level of analgesia may not be the most relevant endpoint.
“We are increasingly evaluating change in patient function, which may be a more useful tool for evaluating the efficacy of pain control,” Dr. Brose said.