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Context: Pain is common among cancer patients. The evidence recommends using strong opioids in moderate to severe cancer pain. No conclusive evidence supports the effectiveness of adding acetaminophen to patients with cancer pain who are already using this regime., Objectives: To assess the analgesic efficacy of acetaminophen in hospitalized cancer patients with moderate to severe pain receiving strong opioids., Methods: In this randomized blinded clinical trial, hospitalized cancer patients with moderate or severe acute pain managed with strong opioids were randomized to acetaminophen or placebo. The primary outcome was pain intensity difference between baseline and 48 hours using the Visual Numeric Rating Scales (VNRS). Secondary outcomes included change in morphine equivalent daily dose (MEDD), and patients' perception of improved pain control., Results: Among 112 randomized patients, 56 patients received placebo, 56 acetaminophen. Mean (standard deviation [SD]) decrease in pain intensity (VNRS) at 48 hours were 2.7 (2.5) and 2.3 (2.3), respectively (95% Confidence Interval (CI) [-0.49; 1.32]; P = 0.37). Mean (SD) change in MEDD was 13.9 (33.0) mg/day and 22.4 (57.7), respectively (95% CI [-9.24; 26.1]; P = 0.35). The proportion of patients perceiving pain control improvement after 48 hours was 82% in the placebo and 80% in the acetaminophen arms (P = 0.81)., Conclusion: Among patients with cancer pain on strong opioid regime, acetaminophen may not improve pain control, or decrease total opioid use. These results add to the current evidence available suggesting not to use acetaminophen as an adjuvant for advanced cancer patients with moderate to severe cancer pain who are on strong opioids., Competing Interests: DISCLOSURES AND ACKNOWLEDGMENTS This is an investigator-initiated trial funded by the Chilean National Grant for Research and Development in Health (Fondo Nacional de Innovación y Desarrollo en Salud - FONISSA18I0039). The PI and sponsor of this research project is Ofelia Leiva. This research project did not have financial support by the industry. The investigators maintain full autonomy in the design, conduct, analyses, and reporting of the study. The author declare that they do not have any conflict of interest. The authors retained full control of the primary data. This study was supported by various medical professionals, nursing, and residents. The authors are grateful to the patients and their families. On the other hand, this study was possible for funding from the Chilean National Grant for Research and Development in Health (Fondo Nacional de Innovación y Desarrollo en Salud – FONIS). All authors read, commented on, and approved the final manuscript., (Copyright © 2023 American Academy of Hospice and Palliative Medicine. Published by Elsevier Inc. All rights reserved.)

Background: Cancer pain is one of the most frequent and relevant symptoms in cancer patients and impacts on patient's quality of life. International and local standards recommend as an initial strategy the use of an analgesic scheme composed of strong opioids associated with adjuvants such as acetaminophen, based upon the assumption that combining drugs could have a better analgesic effect, could allow lowering opioid dosing, and could prevent the occurrence of adverse effects of opioids. However, there is uncertainty about the impact of acetaminophen as an adjuvant in patients who use strong opioids for moderate to severe pain management in cancer patients. The aim of this study is to assess the efficacy and safety of intravenous acetaminophen associated with strong opioids in hospitalized adult cancer patients who have moderate to severe cancer-related pain., Methods: We will perform a randomized double-blinded controlled study comparing intravenous acetaminophen 1 g 4 times a day versus placebo for 48 h as an adjuvant to strong opioids. We will assess pain intensity as a primary outcome, using the verbal numerical rating scale (VNRS, I0 to 10 scale with higher scores meaning higher pain intensity), and we will compare the mean difference in pain intensity between baseline and 48 h among the placebo and intervention groups. We estimate that a decrease of 1 point in the VNRS would be clinically significant. Assuming a standard deviation in pain intensity of 1.7 points, an alpha of 0.025, and a power of 0.8, we estimate a sample size of 112 patients, with 56 patients in each arm. Secondary outcomes include the difference in total opioid use between baseline and at 48 h among the groups, and adverse effects such as drowsiness, constipation, nausea, and vomiting would be evaluated., Discussion: The randomized, double-blind, placebo-controlled design is the best strategy to assess the efficacy of acetaminophen as an adjuvant in adult cancer patients with moderate to severe pain who are receiving strong opioids. We expect to contribute to national and international guidelines with these results., Trial Registration: Clinicaltrials.gov NCT04779567 . Registered on March 3, 2021. Retrospectively registered., (© 2022. The Author(s).)