Pharmacokinetics of clonidine and its relation to the hypotensive effect in patients.

1 The kinetics of clonidine and its relation to the blood pressure response after single intravenous doses of 75 micrograms--275 micrograms in hypertensive patients were determined. 2 Clonidine disposition could be described by a two compartment open model and pharmacokinetic parameters show a rapid distribution phase of 20--30 min and a mean plasma clearance of 4.6 ml min-1 kg-1 (75--200 microgram). The half-life of the beta-phase was found to be in the range of 7.4--11.4 h. Indications of dose dependent kinetics were obtained. 3 A dose-dependent decrease in blood pressure was obtained. 4 The maximal reduction in MAP (mean arterial blood pressure) was significantly (P less than 0.01) related to plasma concentrations of clonidine. 5 The reduction in MAP was always related to plasma concentrations of clonidine (r = 0.88, P less than 0.01) when pseudoequilibrium of distribution of the drug was achieved.