Background: Cancer pain has variable responses to different opioids. Opioid switching is recommended if a lack of effect or adverse effects are seen, and studies of opioid switching observe improved pain outcomes. We aimed to characterise patients with advanced cancer requiring an opioid switch, compared to a control group on stable opioid doses, and to report opioid doses after switch.

 

Methods: This prospective longitudinal study recruited consecutive adult patients from 5 Australian centres. Decision for opioid switch was based on palliative care physician decision. Paired data include pain characteristics, side effects, and treatment efficacy at baseline (T0) and 7 days (T1) using validated instruments. Wilcoxon signed-rank test was used. 

 

Results: 58 patients (24 control, 34 switch) were recruited. At baseline, the switch group experienced more severe pain than the control group (worst pain 8 vs 6/10). Opioid switch resulted in significantly improved average pain (pain 5->4, p.004), function (7->4.5, p.003), mood (7->5, p.05), and sleep (7->4, p.01) at T1 vs T0. Clinicians rated superior global improvement in switch group (mean efficacy index 2.22 vs 1.52; p<0.05).

 

To achieve final stable dose, median oral morphine equivalent daily dose (oMEDD) increased by more than two-fold for those switched to hydromorphone (2.2 fold) and morphine (2.1 fold), but reduced for oxycodone (0.9 fold) and fentanyl (0.8 fold). Patients switched to another opioid had a better improvement in pain than control patients. This was particularly true when different SR and IR opioids were used in combination post-switch.

 

Conclusions: Opioid switching significantly reduces cancer pain and associated symptoms. Final stable switched opioid dose in oMEDD varies between opioids. It is not known whether this reflects a variable effect from opioids or that opioid conversion tables are not accurate in chronic cancer pain.