ANALGESIC EFFECTS OF DIHYDROCODEINE AND TRAMADOL WHEN ADMINISTERED EITHER IN THE MORNING OR EVENING

The aim of the study was to investigate the analgesic effects of two o pioids [dihydrocodeine (DHC) and tramadol] when administered either in the morning or evening. The experimental technique used is based on c hemosomatosensory event-related potentials (CSSERPs) in response to pa inful chemical stimuli that are applied to the nasal mucosa. Eighteen healthy volunteers participated in the experiments. The study followed a controlled, randomized, double-blind, sixfold, cross-over design. T hus, each of the three medications (90 mg DHC, 50 mg tramadol, or plac ebo) was perorally administered to all subjects on different days at 0 8:00 or 20:00 h. Measurements were performed before and 60, 120, 240, and 360 min after administration of the medication. In addition to the assessment of CSSERP, subjects rated the intensity of the stimuli. Mo reover, unspecific drug effects were monitored by means of acoustical event-related potentials and the subjects' performance in a video game . The results indicated that the painful intensity of th chemical stim uli strongly increased during evening sessions. In addition, both DHC and tramadol exerted stronger analgesic effects when administered in t he evening. Thus, an inflexible scheme of prescription might produce e ither an increase of pain in the morning due to insufficient analgesia or the unnecessary overdosing of analgesics in the evening.