Researchers in Japan have found that evening administration of the central alpha(2)-agonists guanabenz and clonidine effectively suppresses elevated blood pressure in the morning in hypertensive patients. The study was done on 133 patients with morning hypertension to receive once-daily evening administration of guanabenz or clonidine for four weeks. The blood pressure lowering effects of the two drugs in the morning and evening were evaluated by patients by monitoring themselves in their own homes. The patients were then sub-divided into different groups according to their evening blood pressure.
The researchers assessed the evening/morning ratio to assess the duration of action of the two drugs. The researchers found that evening dosing with guanabenz and clonidine lowered morning blood pressure significantly. Individual evening/morning ratios for guanabenz, but not for clonidine, were significantly greater in patients whose evening blood pressure was high than in those in whom it was normal. Early during treatment, guanabenz produced a higher diastolic evening/morning ratio than clonidine in patients with a high evening diastolic blood pressure.