Monitoring of opioid therapy in advanced cancer pain patients.

Until now, there have not been any parameters to monitor opioid therapy in cancer patients with pain. In this study, 325 consecutive advanced cancer patients were scheduled for a prospective longitudinal survey. After exclusions, 67 patients were surveyed. All included patients were advanced cancer patients with pain that required opioid therapy for more than 6 weeks before death. Opioid escalation, symptoms associated with opioid therapy, pain mechanism, and pain intensity were recorded. Indices were calculated to categorize the response to opioids. The opioid escalation index (OEI) was used to index the mean increase of the starting opioid dosage, expressed as a percentage or in mg. The length of the period of stable dose (MLD) and the effective analgesic score (EAS), that is, the analgesic consumption/pain relief ratio calculated at fixed intervals, were also used. Patients with a mean visual analogue scale score (VAS) of less than 4 and regular OEI and EAS were considered responsive; patients with a mean VAS less than 4 but with an OEI more than 5 or increases of more than 100% of EAS when compared to that calculated the week before were considered mildly responsive; and patients with a mean VAS more than 4 were considered unresponsive. Advanced age, female gender, and previous chemotherapy were all factors reducing OEI. Head and neck cancer was associated with a higher OEI. Regarding the influence of the opioid-related symptoms, an increased OEI was associated with the presence of confusion. Moreover the presence of confusion was associated with neuropathic pain. Neuropathic pain taken alone, however, did not influence this score. Gender-specific cancer, such as breast cancer, influenced the gender differences reported for MLD (significantly longer than that reported for males and other primary tumor). Good responsiveness was observed in 28 patients, partial responsiveness in 33 patients, unresponsiveness in six patients. Psychological factors were associated with poor pain relief, probably reducing the patient's compliance. The tools used in this study may be useful in monitoring the effects of opioid therapy in cancer pain patients. Simple numbers are easy to compare and make it possible to profile opioid responsiveness and differences among patients.