Oral clonidine premedication reduces the awakening concentration of propofol.

UNLABELLED: To investigate the effects of oral clonidine premedication on emergence from propofol/fentanyl anesthesia, we studied 72 healthy male patients who were undergoing elective orthopedic surgery: the Control group, the 2.5 microg/kg Clonidine group, and the 5.0 microg/kg Clonidine group (n = 24 each). Nothing was administered to the Control group. Clonidine (2.5 or 5.0 microg/kg) was orally administered 90 min before the induction of anesthesia in the Clonidine groups. Patients were anesthetized with computer-assisted continuous infusion of propofol and fentanyl, with the three groups receiving the same concentrations of propofol (3 microg/mL) and fentanyl (1 ng/mL) starting 20 to 30 min before the end of surgery. Propofol infusion was then abruptly discontinued at the end of surgery in all patients. After propofol was discontinued, the response to verbal commands was evaluated every 30 s, and arterial blood samples for propofol and clonidine concentrations were taken when the patients opened their eyes. The time required to respond to a verbal command was 14.9 plus/minus 8.3 min for the 5.0 microg/kg Clonidine group, and this was significantly longer than the Control (8.2 plus/minus 5.0 min) and the 2.5 microg/kg Clonidine (9.0 plus/minus 3.7 min) groups (P < 0.01). Serum propofol concentration at awakening in the 5.0 microg/kg Clonidine group was 1.0 plus/minus 0.4 microg/mL, which was significantly smaller than the Control (1.6 plus/minus 0.4 microg/mL) and the 2.5 microg/kg Clonidine (1.4 plus/minus 0.3 microg/mL) groups (P < 0.01). The blood clonidine concentration was associated with a decrease in the awakening propofol concentration. In conclusion, 5 microg/kg oral clonidine premedication decreases the awakening propofol concentration and delays arousal from propofol/fentanyl anesthesia. IMPLICATIONS: Preanesthetic medication with 5 microg/kg oral clonidine, but not 2.5 microg/kg clonidine, is associated with prolonged recovery from propofol/fentanyl anesthesia.