The Burden of Opioid Adverse Events and the Influence on Cancer Patients' Symptomatology.

CONTEXT: Opioids are frequently used for the treatment of moderate-to-severe pain and their use may produce a number of unwanted adverse events (AEs).

OBJECTIVES: The objective of this study was to understand the burden of opioid-induced AEs in cancer patients with pain after the introduction of strong opioids (WHO Step III).

METHODS: This is a cohort study derived from a randomized controlled trial involving 498 cancer patients with pain who received strong opioids. During 28-day follow-up, we analyzed frequency, intensity, and changes over time of the main opioid-induced AEs; the influence of previous pain therapy on AEs; and the relationships between the presence of AEs and analgesic response.

RESULTS: After starting strong opioids, dry mouth, nausea, and vomiting immediately increased and persisted over time, constipation continued to increase, while drowsiness and confusion tended to decrease. Patients previously treated with weak opioids had more frequent and severe AEs. While at all observation points the percentage of patients without AEs was 37%-39%, considering all the five scheduled visits, from Day 3 to Day 28, 17% of patients never experienced any AEs, while 48% of patients had four or more concomitant AEs. Patients with no AEs experienced significantly lower pain intensity.

CONCLUSION: Opioid introduction induces various AEs that persist over time and worse patients' symptomatology. Moreover, there seems to be a different expression of the opioid toxicity among patients, and a possible interaction between AEs and the analgesic response. The balance between the opioids analgesic effect and induced toxicity is fundamental in deciding the best management for pain in cancer patients.