Investigation of an opioid response categorization in advanced cancer patients

The aim of this study was to investigate a possible distinction in three categories of opioid response and to identify possible factors associated with a poor response. A prospective survey was carried out in 105 consecutive patients requiring morphine for at least 4 weeks before death. Mean pain intensity, opioid doses and symptom intensity at weekly intervals, pain syndromes, and the presence of psychological distress were assessed. Opioid escalation index (OEI%) was calculated from the parameters recorded. Three categories were considered, including (1) patients with slow increments of opioid dose and a mean analgesic 10-cm visual analogue scale (VAS) less than 4 (responders), (2) patients with an OEI% more than 5 but a mean VAS less than 4 (partial responders), and (3) patients with a mean VAS more than 4 (poor responders). Treating physicians were asked to make a judgment on the pain treatment difficulties on a numerical scale (0-10). Significant differences in opioid starting dose (OSD), opioid dose at -4 weeks, nausea and vomiting at -1 week, opioid maximum doses, mean VAS, and OEI were found in the three categories of response. Significant correlations with the physician judgment were found for opioid maximum dose, mean VAS, VAS at the different time intervals, the doses used at the different intervals, OEI, and confusion. Neuropathic pain was significantly associated with a judgment of poor pain outcome. The correlation between the physician judgment and the categories of opioid response was highly significant. Seven of the 12 patients in the third category (poor response) were considered as having a relevant psychological distress. The categorization of the opioid response used in this study could be used in clinical research and as an audit tool, and could be tested in other settings to compare different treatments.