[Prolongation of fentanyl-induced decreased arousal by clonidine]

Both fentanyl and clonidine lead to a reduction of vigilance. We tested the influence of clonidine on a fentanyl induced change of vigilance using a cross-out concentration test (b-cross-out test). With local ethics committee approval, we conducted a randomised double-blinded cross-over study with 10 healthy male subjects (25-35 years old). Each volunteer received intravenously at two separate sessions 1.5 micrograms/kg fentanyl and 1.5 micrograms/kg fentanyl plus 3 micrograms/kg clonidine. For testing the level of vigilance a concentration test (b-cross-out) was used. The number of correctly revised marks was evaluated prior to drug administration (TI), directly after application, one hour later and two hours later. Our data underwent a multiple analysis of variance. With fentanyl two hours after application the mean increase of correctly revised marks was 12% when compared to those prior to application (p < 0.024). This means that with fentanyl a learning effect was achieved as described in the literature. With fentanyl and clonidine two hours after application, a decrease in vigilance of 7 1/4 in comparison with TI was seen (n.s.). This reduction of vigilance should be considered during the postoperative course and especially with regard to ambulant anaesthesia when using clonidine.