Discrepancy between clinic and ambulatory blood pressure measurement in the evaluation of two antihypertensive agents

Discrepancies between clinic and ambulatory BP measurements may be important in the assessment of antihypertensive drug efficacy. Trimazosin (50-200 mg twice daily) and propranolol (40-160 mg twice daily) were compared in 22 hypertensive subjects in a randomised double-blind cross-over study. Daytime ambulatory BP was measured with a non-invasive portable recorder (Remler M2000). Clinic BP measurements were made with a random zero sphygmomanometer. While both drugs reduced clinic supine BP (trimazosin by 16/10 mmHg, P less than 0.01/P less than 0.001; propranolol by 25/14 mmHg, P less than 0.001/P less than 0.001), equivalent decreases on ambulatory measurement occurred with propranolol (28/11 mm/Hg, P less than 0.001/P less than 0.001) but not trimazosin (8/3 mmHg, P less than 0.05/NS). This difference in drug efficacy persisted throughout the 12-hour dosing interval. We conclude that clinic BP measurements alone cannot be relied upon to reflect accurately changes in BP induced by antihypertensive drugs. Moreover this study confirms the necessity for ambulatory BP measurement in the evaluation of antihypertensive drugs.