[Clinical pharmacology of the antihypertensive action of guanfacine].

The clinical pharmacology of a central antihypertensive drug, guanfacine, was studied in sustained essential hypertension. The study of the haemodynamics, performed in 7 patients demonstrated a significant decrease in blood pressure and a fall in heart rate (less than the one observed with clonidine): the peripheral resistances remained unchanged after 4 days treatment. A clinical trial was carried out in 20 patients with sustained essential hypertension. Guanfacine was given orally (2 to 4 mg/day) during 2 months; the results of this study confirmed the antihypertensive effect of the drug. The most frequent side effects were dryness of the mouth and sleepiness. Guanfacine kinetics were studied in patients after single and repeated oral doses. The plasma concentrations were fitted in a two compartments open model with first order absorption. Steady state plasma level during a long term treatment can be determined with the predicted values derived from simulation of the initial individual kinetic studies. For a 2 mg dosage the biological half-life was 22.8 +/- 3.6 h. Guanfacine kinetics were linear according to the dosage. In moderate permanent essential hypertension guanfacine can be easily prescribed in monotherapy at a posology of 2 to 4 mg/day.