Background Cancer pain guidelines call for early opioid initiation. However, the timing of opioid initiation in relation to advanced cancer diagnosis has not been elucidated. The most frequent opioid used differs according to country and region, and the timing and frequency surrounding opioid switching in Australia also not been clearly documented. The role of palliative care teams in initiating opioids for advanced cancer is also unclear.

Aim To determine the timing of opioid initiation and switching by prescriber and cancer type, in relation to key timepoints in the cancer illness course (diagnosis, palliative care referral, and death).

Design Retrospective cohort study.

Setting/Participants Patients at a quaternary cancer centre diagnosed with incurable advanced biliary/liver, colorectal, lung, renal/bladder, and pancreatic cancers between 1 August 2020 – 1 August 2022 were eligible. Demographics, clinical characteristics, health service use, and details of longitudinal slow and immediate release opioid prescriptions are reported.

Results Among 200 patients, median time from advanced cancer diagnosis to first immediate release opioid prescription was 23 days (IQR 1, 82) and to slow release opioid prescription was 47 days (IQR 14, 155). Most patients (95%, (n=190) were referred to palliative care (median time to referral 54 days (IQR 18, 190)). Non-palliative care prescribers initiated slow release opioids for half of participants (49%, n=97) prior to referral. Patients with pancreatic cancer had earliest time to slow/immediate release opioid prescription (median 10 days (IQR 0, 39) and 26 days (IQR 1, 43) respectively) and shortest survival (median 136 days (IQR 82, 214)).

Over half (58%) patients underwent opioid switching at least once. Of these, approximately two-thirds switched due to uncontrolled pain or adverse effects and the remainder switched due to need to use a separate route for clinical reasons. Over a quarter (28%) switched opioids twice and 8% switched three times. The opioid dose threshold for switching appeared to be almost always approximately double of the opioid starting dose.

Discussion/Conclusions Time from diagnosis of advanced cancer to opioid commencement is short (median 3 weeks). Therefore people with advanced cancer require early pain intervention and management within the first month after diagnosis. Median time from opioid commencement to death was 4 months and this may mitigate patient and prescriber concerns around opioid tolerance and dependence which often develop over longer time periods.

Opioid switching is more common in our centre compared to the available data published in Europe. Potential reasons for this will be discussed. Time to opioid initiation varies according to cancer type, suggesting a difference in pain presentations. Diagnosis of advanced pancreatic cancer is associated earlier opioid commencement. People with pancreatic cancer may benefit from routine early referral to palliative care services to coordinate complex pain management needs due to earlier pain presentations and shorter prognosis.