Effectiveness of topical administration of opioids in palliative care: a systematic review.

The discovery of peripheral opioid receptors has become the scientific basis for topical use of opioids in malignant and nonmalignant ulcers and oropharyngeal mucositis. This systematic review aimed to assess the quality of published literature and to examine whether topical opioids are effective in controlling pain in palliative care settings. After a systematic literature review, 19 studies (six randomized controlled trials [RCTs] and 13 case reports) met the inclusion criteria for the review. Eighteen studies favored topical opioids in pain relief, as evidenced by reductions in post-treatment pain scores, but time to onset and duration of analgesia varied widely. Because of the heterogeneity of the studies, meta-analysis was not possible. Despite clear clinical benefits described in small RCTs, there is a deficiency of higher-quality evidence on the role of topical opioids, and more robust primary studies are required to inform practice recommendations. N-of-1 trials should be encouraged for specific clinical circumstances.