Measuring the efficacy of antihypertensive therapy by ambulatory blood pressure monitoring in the primary care setting.

Background: Traditional clinical trials in hypertension measure the efficacy of antihypertensive drugs but may not fully assess their effectiveness in clinical practice. Community-based trials can provide this information but are limited because usually they are of open-label design and potentially subject to observer bias. Therefore, we used ambulatory blood pressure monitoring (ABPM), an automated and objective measure of blood pressure (BP) to overcome these shortcomings in a large community-based trial.

Methods: Patients with hypertension, either untreated or currently on treatment, were started on, or switched to, the angiotensin receptor blocker telmisartan 40 mg daily; after 2 weeks, if office BP remained > or = 140/85 mm Hg, the dose was increased to 80 mg, and if necessary, hydrochlorothiazide 12.5 mg was added after a further 4 weeks and continued for the final 4-week period. Baseline and treatment ABPM measurements were completed in 940 previously untreated patients and 675 previously treated patients.

Results: The average reduction of the entire cohort was -10.7/-6.5 mm Hg (P < .0001; mean 24-hour BPs were reduced by 12/8 and 8/5 mm Hg in the untreated and previously treated patients, respectively). In contrast, the office BPs fell by an average of 23/12 and 17/10 mm Hg in previously untreated and treated patients. In 401 patients whose baseline 24-hour BP was > or = 130/85 mm Hg, the mean decrease in 24-hour BP was 16.8/11.4 mm Hg. Based on ABPM criteria, the BP was fully controlled (< 130/85 mm Hg) in 70% of patients, and based on office measurement criteria (< 140/90 mm Hg), in 79%.

Conclusions: Ambulatory BP monitoring demonstrated excellent control rates by telmisartan monotherapy or in combination with hydrochlorothiazide. Observer and measurement bias was substantial based on the changes from baseline by clinical measurements in contrast to ambulatory BP recordings. The successful use of this procedure in primary care research will create further opportunities to define the effectiveness of treatment in the environment in which it is customarily prescribed.