Lack of Efficacy: When Opioids Do Not Achieve Analgesia from the Beginning of Treatment in Cancer Patients

INTRODUCTION: Opioids are often used to relieve moderate to severe pain, but their analgesic response may vary. We focused on the absolute lack of analgesic response immediately after beginning opioid treatment, quantifying the proportion of patients with unchanged or worse pain on day 3 (defined as early non-responders (ENRs)) and day 7. METHODS: This is a post-hoc analysis from a randomized controlled trial involving 498 cancer patients with pain, starting to receive WHO step III opioids. On days 1, 3 and 7 pain intensity (PI) was measured. RESULTS: On day 3, 68 (13.7%) patients were ENRs, 53 no change and 15 greater PI compared to baseline. The relationships between pain and clinical characteristics showed no significant differences between ENRs and Early responders (ERs), except for PI at baseline, which was significantly lower in ENRs. ENRs on day 3 were re-assessed on day 7 to explore the patterns of analgesic response: 31.7% of patients remained NRs, 48.3% had become responders, and 20.0% were poor responders. Adverse drug reactions were similar in ERs and ENRs at each visit. DISCUSSION: The complete lack of early response to opioids in cancer patients is clinically important and more frequent than expected. Better definition of the mechanism will allow better pain management in cancer and non-cancer patients.