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.

Growth hormone and cortisol secretion after oral clonidine in healthy adults

The purpose of this study was to evaluate oral clonidine for testing growth hormone (GH) responsiveness in healthy adults. Oral clonidine (0.15 mg) produced a satisfactory GH response (greater than 4 ng/ml from basal) in eight out of 10 subjects, which is similar to rates reported after an equivalent intravenous dose. Elevated GH levels at baseline occurred in four out of five female subjects; this did not affect the clonidine-induced GH release. There were no significant differences at any time point in plasma prolactin or cortisol levels following clonidine, compared to placebo controls. Adequate plasma clonidine levels (greater than 0.4 ng/ml) were achieved in all subjects, with corresponding reductions in mean arterial blood pressure, but with only minimal adverse effects. Results from this study indicate that oral clonidine is a reliable method for testing GH responsiveness in adult subjects.