Moxonidine: a review of safety and tolerability after seven years of clinical experience.

Centrally acting antihypertensive drugs, or sympatholytics, (reserpine, methyldopa and clonidine) have a long history of efficacy but are now little used in most countries. One of the most important reasons for this is relatively poor tolerability compared to many newer agents. In the case of clonidine there is also the potential danger of rebound hypertension. The most prominent adverse effects have been dry mouth, sedation, dizziness and oedema. These reactions, especially the first two, are thought to be associated with activation of central nervous system and salivary gland alpha2-adrenergic receptors. In the last 15 years it has become possible to produce drugs with selective agonist effect on another class of brainstem receptors, the imidazoline I1-receptors, which appear to have modulate sympathetic activity and blood pressure without affecting alertness or salivary flow: however, they still have some action on alpha2-receptors. Moxonidine and rilmenidine are moderately selective imidazoline agonists which have been in clinical use for several years in many European countries. Trial evidence and postmarketing surveillance indicate that moxonidine may cause dry mouth or sedation in a minority (<10%) of patients, significantly less than with the older drugs. There is no significant incidence of oedema and unexpected or idiosyncratic adverse effects are extremely rare. Moxonidine may improve aspects of glucose and lipid metabolism. In conclusion, moxonidine is a safe as well as an effective antihypertensive, with considerably improved patient tolerability compared to the older sympatholytics.