Comparative studies of guanfacine and methyldopa.

1. The antihypertensive effects of the new phenylacetylguanidine compound, guanfacine, a sympathetic inhibitor with a central site of action, were compared with methyldopa in 20 out-patients with essential or renal hypertension (WHO grade I-II). 2. During a 6-week period in randomized cross-over conditions, guanfacine 3.5 mg daily caused a mean decrease of 24% in mean arterial blood pressure (MAP). A normalization of blood pressure (BP < 145/95 mm Hg) was achieved in 50% of the patients and a 'good control' (BP < 160/100 mm Hg; > 145/95 mm Hg) in 90%. 3. Methyldopa 1.2 g daily led to a mean decrease in MAP of 12%. Normalization of blood pressure occurred in 15% and a 'good control' was achieved with 45% of the patients. Failure due to intolerance or ineffectiveness was observed in 40% of patients. 4. During therapy with guanfacine the following side-effects were noted: dryness of the mouth (n = 5), marked sedation (n = 2), constipation (n = 2), orthostasis (n = 1), collapse (n = 1) and atrioventricular block grade I on ECG (n = 1). Methyldopa caused headaches (n = 4), gastrointestinal disturbances (n = 4) and dryness of the mouth (n = 1). 5. The experience so far available seems to indicate that guanfacine is an effective antihypertensive drug which is more active than methyldopa in the doses used in this study.