Does isradipine exert a special early-morning blood pressure-lowering effect?

The blood pressure-lowering effect of isradipine at 1.25-2.5 mg twice daily (taken at 0700 and 1900 h) was assessed in a double-blind study involving 28 men with mild-to-moderate hypertension. After a 4-week placebo period, patients were randomized to receive either isradipine (group I) or placebo (group II) for 8 weeks. At the end of the placebo and active-treatment periods, patients were evaluated by 24-h ambulatory blood pressure monitoring. Data were analyzed according to two time periods: daytime, 1000-2300 h; nighttime and early morning, 2300-1000 h. Intersubject analyses were performed comparing values at the end of placebo with those at the end of active treatment. Intrasubject two-way analysis of variance showed that the time of day or night had no influence on blood pressure changes. Comparison of systolic (SBP) and diastolic (DBP) blood pressures with isradipine indicated that there were significantly greater average decreases in SBP at 0600-0800 h than at 1800-2000 h (p = 0.038), and at 0800-1100 h than at 2000-2300 h (p = 0.045). This was also true for the average decreases in DBP (p = 0.006). In conclusion, isradipine exerts blood pressure control throughout 24 h with a pronounced action during the early morning (0600-0800 h) period.