Conduct of therapeutic trials

Ambulatory blood pressure monitoring (ABPM) is now very useful for assessing the blood pressure response to antihypertensive drugs. It gives accurate information on blood pressure profiles and provides more detailed information on first-dose effects, dose-response relationships, and the direction of action of antihypertensive treatment. However, ABPM studies will also allow new questions to be addressed. The reliability of ABPM measurements must receive more attention: validation of the different ABP monitors, evaluation of missed data, standardization of activities during the monitoring period. Concerning these technical problems, it seems reasonable to propose a control of quality of ABPM data in therapeutic trials. As a result of previous studies, it might be argued that ABPM should not obly be used to evaluate the effects of treatment, but also to improve the selection of patients for clinical trials who are hypertensive both in the clinic and during ABPM. Despite a generally good agreement between sthe effects of medication on clinic and ABP when analysed on a group basis, several studies have reported weak, insignificant correlations on an individual basis, indicating discrepancies between clinic and ambulatory pressures. Clinic pressures tend to overestimate the degree of blood pressure control during daily activities. Treatment produces a significant reduction in ABP in the 'true hypertensives', whereas in the other 'white-coat hypertensives' it has no effect. There is also a question of the duration of action of treatment: whether medication should be equally effective throughout the day and night or should be focused on moments when the pressure is highest. The value of blood pressure variability in therapeutic trials is not yet well known, and needs further evaluation. The definition of hypertension and normotension have traditionally been difficult and arbitrary when based on clinic blood pressure measurements, the difficulty is not removed when trying to achieve a definition of normal blood pressure by using ABPM, the predictive value of which is still being tested.