Continuous reaction time after single dose, long-term oral and epidural opioid administration.

Auditory continuous reaction time was studied in three treatment groups. Twenty opioid naive patients received intramuscular morphine 0.15 mg kg-1 bodyweight for premedication. Thirty-one cancer patients were treated with oral opioids, 180 mg morphine per 24 h (median). Twenty-two cancer patients were treated with epidural morphine, 79 mg morphine per 24 h (median). The treatment groups were compared to a control group of 44 healthy persons taking no analgesics. The reaction time was measured using 152 auditory signals and summarized as 10%, 50% and 90% percentiles. Analysing reaction time distributions, the opioid naive patients showed the greatest difference to the control group in the shortest reaction times while chronic opioid users showed the greatest difference for the longest reaction times. There seems to be a qualitative difference in reaction time distribution, between opioid naive individuals treated with single dose morphine and cancer patients in long-term treatment.