Objective: To assess whether topical morphine is pharmacologically effective in relieving pain from ulcers caused by arterial insufficiency and identify whether this effect is centrally or peripherally mediated.
Method: The analgesic effect of a topically applied hydrogel containing 0.5% of morphine was evaluated in a double-blind, placebo-controlled, three-way crossover pilot study involving nine patients with painful arterial leg ulcers. All patients had a baseline pain intensity of at least 5 on a 10-point numeric rating scale. They received the following three treatments in random order: morphine hydrogel plus a subcutaneous (SC) placebo infusion; placebo gel plus a SC infusion of 5mg morphine over six hours and a placebo gel plus a SC placebo infusion. Each treatment lasted one day. Pain was assessed during the first 24 hours after application of the hydrogel and the start of the subcutaneous infusion.
Results: There was a statistically significant difference between average baseline pain scores and those reported during treatment, but this difference was not clinically relevant. The three treatments did not differ in terms of the pain relief provided.
Conclusion: Topical morphine does not have a clinically relevant analgesic effect in patients with painful arterial leg ulcers. Further research should focus on ulcers of other aetiology.