Oral Clonidine Premedication Does Not Alter the Efficacy of Simulated Intravenous Test Dose Containing Low Dose Epinephrine in Awake Volunteers

Background: Clonidine premedication modifies the hemodynamic responses to sympathomimetics. The present study was designed to test whether clonidine altered the response to a small intravenous dose of epinephrine, such as that which might be used in an epidural test dose.

Methods: In 18 healthy volunteers, four series of determinations were performed in random order and were separated by a minimum 72 h: (1) no premedication followed by intravenous saline 3 ml, (2) no premedication followed by intravenous test dose containing 3 ml of 1.5% lidocaine + 15 micro gram epinephrine, (3) oral clonidine (5 micro gram/kg 1.5 h before hemodynamic determinations) followed by intravenous saline, and (4) oral clonidine followed by intravenous epinephrine-containing test dose. Systolic blood pressure (SBP) and heart rate (HR) were measured continuously, and symptoms associated with central nervous system toxicity were noted.

Results: After the test dose injections, HR and SBP increased with or without clonidine premedication. The 95% confidence intervals for the maximum HR increases with and without clonidine were 49-61 and 44-54 beats/min, respectively, indicating that one could not be absolutely certain that everyone would develop a positive HR response. The HR increase was >or= to 20 beats/min in 18 of 18 volunteers given epinephrine with or without clonidine and in 0 of 18 volunteers given saline. Calculated sensitivities, specificities, and positive and negative predictive values were all 100% based on the conventional HR criterion and were unaltered by clonidine. Subjective symptoms were not affected by clonidine.