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.