A randomized, double-blind, multi-site, crossover, placebo-controlled equivalence study of morning versus evening once-daily sustained-release morphine sulfate in people with pain from advanced cancer.

Diurnal variation in pain perception is recognized. The question of whether opioid prescribing should be adjusted to account for diurnal variation can be tested with the advent of once-daily sustained-release morphine. The study recruited 45 people with opioid-responsive pain on stable doses of analgesics and advanced cancer from five regional palliative care programs in Australia. Each participant took one placebo and a 24-hourly dose of sustained-release morphine daily, 12 hours apart-active dose in the morning for one week and in the evening for the other week. The order of the weeks was randomized in a double-blind manner. The primary outcome from the last two days (steady state) on both arms was averaged four-hourly pain scores while awake on a 100 mm visual analogue scale (VAS). Secondary outcomes included VAS and categorical scales for other pain parameters, quality of sleep, nausea, vomiting, constipation, confusion, and somnolence. Twenty-six of 42 participants completed the study and provided adequate power for analysis. Mean VAS was 16 mm for morning dosing and 14 mm for evening dosing (P=0.76, difference of adjusted means 2 mm, 95% confidence interval: -2, 6). No differences were found in pain control, pain during the day, pain disturbing sleep, or with breakthrough medication use. This study suggests that any difference between morning and evening dosing of once-daily sustained-release morphine in people with significant opioid-responsive pain and advanced cancer is small and unlikely to be clinically significant for most people.