Clonidine and guanfacine--comparison of their effects on haemodynamics in hypertension.

The pharmacology of central alpha-adrenoceptor-stimulating agents is discussed, with particular reference to clonidine (Catapres; Boehringer Ingelheim) and guanfacine (Estulic; Sandoz), and their haemodynamic effects are compared and contrasted. The main differences between the effects of clonidine and guanfacine on hypertension are: guanfacine activates presynaptic alpha-adrenoceptors 10 times more selectively than clonidine; guanfacine has an alpha 2/alpha 1-selectivity ration 25 times higher than clonidine; clonidine decreases cardiac output and guanfacine decreases peripheral resistance, clonidine has no effect on stroke volume but guanfacine increases it; and when the clonidine withdrawal syndrome in the spontaneously hypertensive rat is compared with cessation of guanfacine treatment at an equipotent antihypertensive dose, the withdrawal syndrome after guanfacine appears later and is much less severe. Guanfacine may be preferable to clonidine as a central alpha-adrenoceptor stimulant in the treatment of hypertension.