Study Objective: To determine the effects of oral clonidine premedication on hemodynamic changes during the entire course of ketamine anesthesia and incidence of postoperative adverse reactions.

Design: Randomized, prospective, double-blind, placebo-controlled study.

Setting: Department of Anesthesiology, University of Tsukuba Hospital, Ibaraki, Japan.

Patients: 39 ASA physical status I and II patients undergoing superficial surgeries.

Interventions: Placebo, clonidine 2.5 μg/kg, and clonidine 5 μg/kg groups received respective doses of oral clonidine 90 minutes prior to surgery. Anesthesia was induced with ketamine 2 mg/kg intravenously (IV), trachea was intubated, and anesthesia was maintained with 67% nitrous oxide, oxygen, and supplemental ketamine (1 mg/kg) when systolic blood pressure and heart rate (HR) exceeded 180 mmHg and 100 bpm, respectively.

Measurements and Main Results: In the clonidine 2.5 μg/kg group, HR response to tracheal intubation was significantly less, while in the clonidine 5 μg/kg group both mean arterial pressure and HR responses were significantly suppressed, compared with the placebo group. Intraoperative coefficients of variations of HR were significantly less in both clonidine groups than the placebo group. Incidence of nightmare and degree of salivation were significantly less in the clonidine 5 μg/kg group than in the placebo group.

Conclusion: Oral clonidine 2.5 μg/kg and clonidine 5 μg/kg attenuates cardiostimulatory effects, while clonidine 5 μg/kg was associated with reduced incidence and severity of nightmare and salivation attributable to IV ketamine.