Antihypertensive efficacy of the calcium-antagonist felodipine in patients with persisting hypertension on beta-adrenoceptor blocker therapy. The Canadian Felodipine Study Group.

1. The antihypertensive efficacy of two different doses of the calcium antagonist felodipine was evaluated in patients with hypertension persisting despite beta-adrenoceptor blocker therapy. Following a single-blind placebo period of 4 weeks, patients were randomized to placebo (n = 36), felodipine 5 mg twice daily (n = 39) and felodipine 10 mg twice daily (n = 35) for another 4 weeks. beta-adrenoceptor blocker therapy remained unchanged throughout the study. 2. Effects on blood pressure (BP) were evaluated after the first dose and after chronic dosing at 2 h after dosing and the end of the dosing interval (12 h). 3. Felodipine decreased systolic and diastolic BP by 30-35/20-25 mm Hg at 2 h. These decreases were similar after acute and chronic treatment. Twelve hours after dosing, decreases of 15-20/10-15 mm Hg were observed compared to 10/5 mm Hg on placebo, and half of the patients still had a controlled BP (supine diastolic BP less than 90 mm Hg). BP responses were rather similar for both doses of felodipine at 2 and 12 h. 4. Multiple regression analysis showed that both initial BP level and plasma felodipine concentrations were significant predictors of the BP response to felodipine, but age was not. 5. Adverse effects attributed to felodipine were mainly related to vascular symptoms (primarily flushing and ankle swelling); these occurred in about 30% of patients, and were pronounced in three patients (4%). 6. Felodipine is therefore highly effective in lowering BP of hypertensive patients on chronic beta-adrenoceptor blocker therapy, with no evidence for a gradual lowering of the BP or for development of tolerance. Both initial BP level and plasma concentrations are better indicators of antihypertensive efficacy of this calcium antagonist than age.