Additive Hypotensive Effect of a Dihydropyridine Calcium Antagonist to That Produced by a Thiazide Diuretic: A Double-Blind Placebo-Controlled Crossover Trial with Ambulatory Blood Pressure Monitoring

The study was designed to investigate whether a long-acting dihydropyridine calcium antagonist has additional antihypertensive effect when combined with currently used low-dose thiazide diuretic therapy. After 6 weeks with open chlorthalidone monotherapy at 25 mg daily, hypertensive patients with trough diastolic BP 90-115 mm Hg were randomly assigned to receive double-blind lacidipine, 4 mg daily or matching placebo for 4 weeks, while continuing to receive background chlorthalidone. Then patients crossed over to the alternative regimen for a second 4-week period. Clinic and 24-h ambulatory blood pressure (BP) were measured on the final day of chlorthalidone monotherapy and on the final day of each double-blind treatment. Seventeen patients completed the study [mean age, 51.0 +/- 6.9 (SD) years]. Clinic BP was lower with lacidipine versus placebo (systolic, p < 0.01; diastolic, p < 0.05). Daytime ambulatory BP was reduced with lacidipine (p < 0.05), whereas nighttime BP was unchanged. Mean 24-h ambulatory diastolic BP also was reduced on lacidipine (p < 0.05). Heart rate was increased on lacidipine during both daytime (p < 0.01) and nighttime (p < 0.05). In conclusion, when added to chlorthalidone, lacidipine produced a significant reduction in clinic and ambulatory BP during daytime but not nighttime. This was associated with increased heart rate. Modem long-acting dihydropyridines may produce small but clinically significant additive antihypertensive effects in patients uncontrolled on low-dose thiazide monotherapy.