Does cancer type and adjuvant analgesic prescribing influence opioid dose?-a retrospective cross-sectional study

Opioids are the backbone of cancer pain management. Minimal evidence exists examining the relationship between cancer type and opioid dose. Similarly, the use of adjuvant analgesics and its impact within an inpatient cancer setting is understudied. This study examined the influence of cancer type upon opioid dose, measured by oral morphine equivalent daily dose (oMEDD). The effect of adjuvant analgesics on patient oMEDD was also examined. This retrospective cross-sectional study examined records of 520 patients admitted to Royal Melbourne Hospital or Peter MacCallum Cancer Centre between 2016 and 2018 with advanced cancer. Number and dose of both opioid and adjuvant analgesics were collected along with demographic and cancer data. Comparisons of median oMEDD by cancer type [analysis of variance (ANOVA), non-parametric t-tests] and adjuvant analgesics (Kruskal-Wallis test) were performed. There were no statistically significant differences in oMEDD between the 12 cancer types (P=0.83; n=215). Patients co-prescribed pregabalin (n=102) and paracetamol (n=73) as adjuvant analgesics were on significantly higher daily oMEDD [60 mg (P=0.015), 90 mg (P<0.001), respectively]. Opioid dose did not differ significantly between cancer types. The observed use of adjuvant analgesics coincided with significantly higher oMEDD prescription which may relate to complex pain seen in this cohort of inpatients in a quarternary cancer centre. Future research should focus on pain type and aetiology, and pain scores in different cancer pain syndromes to determine the net effect of opioids and adjuvants in cancer pain prescribing.