The effectiveness of clonidine as an antihypertensive in a two-dose regimen

Efficacy of clonidine as transdermal therapeutic system: the international clinical trial experience

Worldwide clinical trial data concerning the pharmacokinetic and pharmacodynamic characteristics of the clonidine transdermal therapeutic system (TTS) are reviewed with reference to its antihypertensive efficacy. The amount of clonidine delivered to the systemic circulation is a direct function of TTS size. After initial patch application, there is a delay of 2 to 3 days before the onset of action, but after removal of the patch, plasma clonidine levels decline slowly, at an elimination half-life of about 20 hours. Evaluation in approximately 2000 patients with mild to moderate hypertension has shown that the bioavailability of transdermal clonidine is comparable to that of oral clonidine and that equivalent blood pressure reductions are achieved. The rate at which dose increases were found necessary to maintain adequate blood pressure control over extended periods reflects a low incidence of tolerance to this new once-a-week dosage form of clonidine, and there has been little evidence of rebound hypertension after discontinuation of TTS treatment.

Relationship between the cardiovascular effects and steady-state kinetics of clonidine in hypertension. Demonstration of a therapeutic window in man

Clonidine was given orally as monotherapy in increasing daily doses from 3.1 to 25.7 micrograms/kg to patients with essential hypertension (n = 6). When a steady state concentration in plasma was reached at each dose level, the blood pressure (BP) and heart rate were measured during a dosage interval. Effect time-plasma concentration data were submitted to nonlinear regression analysis, which showed that the observed BP effects could be dissociated into depressor and pressor components. A window for the anti-hypertensive effect was established. At a plasma clonidine concentration of 0.65 +/- 0.07 ng/ml 50% of the maximal depressor effect was found, and it was only separated by a factor of 2 from the half maximal pure pressor concentration in plasma. No relationship between the change in heart rate and the plasma clonidine was observed. The findings strengthen the importance of close monitoring of clonidine therapy.