Comparison of speed of onset of analgesic effect of diamorphine and morphine.

In a random, double-blind crossover trial using an ischaemic limb pain model we have assessed the speed of onset of analgesia after an i.v. bolus of equipotent doses of diamorphine and morphine in 12 healthy male volunteers. Pain and its subsequent relief were assessed by means of a visual analogue scale. Two of the subjects found diamorphine acted quicker than morphine, one found no difference and nine found that morphine was quicker than diamorphine. The mean time to diamorphine effect was 53% greater than for morphine (P less than 0.005, Wilcoxon rank sum test). These findings suggest that, for rapid relief of pain, morphine is more suitable than diamorphine.