No pain relief from morphine? Individual variation in sensitivity to morphine and the need to switch to an alternative opioid in cancer patients

Abstract

Goals of work: The aims of this study were (1) to prospectively evaluate the clinical benefits of switching from morphine to an alternative opioid, using oxycodone as first-line alternative opioid, in patients with cancer, (2) to evaluate the consistency of the clinical decision for the need to switch by comparing two hospital sites, and (3) to evaluate whether there were objective predictors that would help identify morphine non-responders who require switching to an alternative opioid and from this to construct a clinical model to predict the need to switch.

Patients and methods: One hundred eighty-six palliative care patients were prospectively recruited from two hospital sites. Responders were patients treated with morphine for more than 4 weeks with good analgesia and minimal side effects. Non-responders (switchers) were patients who had either uncontrolled pain or unacceptable side effects on morphine and therefore required an alternative opioid. The differentiation between responders and switchers was made clinically and later confirmed by objective parameters.

Results: In this prospective study 74% (138/186) had a good response to morphine (responders). One patient was lost to follow up. Twenty-five percent (47/186) did not respond to morphine. These non-responders were switched to alternative opioids (switchers). Furthermore, of 186 patients, 37 achieved a successful outcome when switched to oxycodone and an additional 4 were well controlled when switched to more than one alternative opioid. Overall successful pain control with minimal side effects was achieved in 96% (179/186) of patients. There were no significant differences in the need to switch between the two hospital sites.

Conclusions: This study has shown that proactive clinical identification and management of patients that require opioid switching is reproducible in different clinical settings and significantly improves pain control. Further studies are required to develop and test the predictive model.