Enhancement of pressor response to ephedrine following clonidine medication.
We studied pressor responses and changes in plasma catecholamine concentrations following two consecutive doses of ephedrine 0.1 mg.kg-1 with (n = 20) and without (n = 20) clonidine 5 micrograms.kg-1 premedication in patients presenting for a variety of major surgical procedures under general anaesthesia. Arterial blood pressure and heart rate were measured at 1 min intervals for 10 min, and plasma catecholamines were measured before and 3 min after each dose of ephedrine. Mean blood pressure changes from the baseline values were greater in the clonidine than in the control group 3-8 min and 4-9 min following the first and the second doses of ephedrine, respectively (p < 0.05). Plasma catecholamine concentrations tended to be lower in the clonidine group throughout the study. The augmented pressor response to ephedrine in clonidine-treated patients can be attributed to enhanced cardiovascular response rather than clonidine-induced accumulation and subsequent increased release of catecholamine.
Tanaka
M
M
Department of Anaesthesia/Critical Care Medicine, Tsuchiura Kyodo General Hospital, Japan.
Nishikawa
T
T
D000328:Adult; D000769:Anesthesia, Inhalation; D001794:Blood Pressure / Q000187:drug effects; D003000:Clonidine / Q000494:pharmacology*; D004357:Drug Synergism; D004809:Ephedrine / Q000494:pharmacology*; D004837:Epinephrine / Q000097:blood; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009638:Norepinephrine / Q000097:blood; D011292:Premedication; D013565:Sympatholytics / Q000494:pharmacology*; D013566:Sympathomimetics / Q000494:pharmacology*
D013565:Sympatholytics; D013566:Sympathomimetics; D004809:Ephedrine; D003000:Clonidine; D009638:Norepinephrine; D004837:Epinephrine