Comparison of daily anti-hypertensive effects of amlodipine and nifedipine coat-core using ambulatory blood pressure monitoring - utility of "hypobaric curve" and "hypobaric area"

When selecting anti-hypertensives, most physicians do not consider daily blood pressure (BP) variation. To evaluate the effectiveness of anti-hypertensives on the temporal profile of BP, we proposed three new parameters obtained by ambulatory BP monitoring and evaluated these parameters by comparing 5 mg of amlodipine and 40 mg of nifedipine coat-core. Hypobaric values were determined by subtracting BP data collected before administration of the drug from those collected after drug treatment at the corresponding time of day. The hypobaric curve was drawn by plotting the hypobaric values in chronological order, with the time at which the drug was taken set as the starting point. The hypobaric area was the area encircled between the 0 mmHg level line and the hypobaric curve. For amlodipine, the hypobaric areas of systolic blood pressure (SBP) and diastolic blood pressure (DBP) were -19,110 mmHg/min and -10,695 mmHg/min, respectively. Systolic BP decreased -13.3 mmHg, and DBP BP -7.4 mmHg as daily averages. For nifedipine coat-core, the hypobaric areas of SBP and DBP were -32,235 mmHg/min and -18,150 mmHg/min, respectively. Systolic BP decreased -22.3 mmHg and DBP -12.6 mmHg as daily averages. From the hypobaric curves, the trough-to-peak ratios of amlodipine and nifedipine coat-core were measured as 0.67 and 0.60, respectively. The total anti-hypertensive power of nifedipine coat-core, measured by the hypobaric area, was 1.69 times more potent than that of amlodipine. These parameters seem to be useful for evaluating the daily temporal profile of the BP-lowering effects of anti-hypertensive drugs.