Centrally Acting Drugs (Clonidine, Methyldopa, Guanfacine)

Abstract

A great number of drugs which act upon the CNS also lower blood pressure and heart rate, for example, some hypnotics and narcotic analgesics. These drugs, however, exert other central actions which are more prominent, and therefore the central hypotensive effect might be called nonspecific. The discovery of the antihypertensive action of clonidine and its central mode of action set a new standard for a class of drugs which might be called “specific central antihypertensives” (for reviews, van Zwieten 1975; Schmitt 1977; Kobinger 1978). Although clonidine has CNS side effects, its cardiovascular depressive effects are prominent; despite its peripheral cardiovascular effects, its central site of action is widely agreed to be primarily responsible for the hypotension. The history of reserpine illustrates the difficulty involved in specifying a multiply active drug as being mainly centrally or peripherally active (for review, Kobinger 1984a). The class of clonidine-like hypotensive drugs was first defined by two criteria, namely a direct stimulation of peripheral α-adrenoceptors and a hypotensive effect of CNS origin (Kobinger 1978). By means of these criteria a number of chemically different drugs were classified as members of the same group. Some of them are listed in Fig. 1, including guanfacine.