Opioid substitution to reduce adverse effects in cancer pain management

Objective: To assess the effect of opioid substitution (substituting one member of the opioid class for another) on the incidence and severity of adverse effects in palliative-care patients who experience unacceptable, refractory adverse effects when taking an opioid drug. Design: Prospective audit of clinical records. Setting: Palliative Care Program, Monash Medical Centre, Melbourne, Victoria (comprising an acute 10-bed palliative care unit and a palliative care consultative service). Patients: Ail palliative care inpatients and patients referred to the consultative service who underwent opioid substitution between February 1996 and June 1997. Outcome measures: Adverse effects and pain control profiles before and after opioid substitution. Results: 55 opioid substitutions were undertaken in 49 patients. 49 substitutions were for adverse effects. The substitution produced partial or complete relief from confusion in 18 of 25 cases, from nausea and vomiting in 13 of 19, and from drowsiness in 8 of 15. Substitution also abolished myoclonus associated with renal failure in one patient. Conclusion: We found that the incidence and severity of adverse effects differed between opioids in the same patient. A trial of opioid substitution (usually in consultation with a specialist pain or palliative care unit and with auditing of outcomes) should be considered for patients with intolerable, refractory adverse effects of opioids.