NEW ORLEANS—Daily aspirin taken at bedtime is known to contribute to lower BP levels in patients with hypertension. A new study extends this finding to patients with prehypertension.


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Daily low-dose aspirin taken at bedtime but not during the morning significantly reduces systolic BP (SBP), Ramón C. Hermida, MD, reported here at the 23rd annual meeting of the American Society of Hypertension.


The SBP drop with nighttime dosing of aspirin is consistent with a higher level of activation of the renin-angiotensin system overnight, said Dr. Hermida, director of bioengineering and chronobiology at the University of Vigo in Spain.


The effect of 100 mg of aspirin on SBP was assessed in 244 subjects with prehypertension (defined as SBP of 120-139 mm Hg and/or diastolic BP of 80-90 mm Hg on multiple readings), who received aspirin at different times of the day according to their rest-activity cycle.


They were randomized to one of three groups: one that received hygienic-dietary recommendations only, one that received hygienic-dietary recommendations plus 100 mg of aspirin on awakening, and one that received hygienic-dietary recommendations plus 100 mg of aspirin at bedtime. Blood pressure and heart rate were sampled throughout a 48-hour period, before and after three months of treatment.


There were no changes in ambulatory SBP in either of the groups assigned to hygienic-dietary measures and morning administration of aspirin. The researchers noted, however, that few patients adhered to the hygienic-dietary recommendations. In contrast, the group assigned to aspirin at bedtime had reductions in SBP in excess of 5 mm Hg compared with baseline during awake hours, asleep, and over 24 hours without any change in heart rate or physical activity compared with baseline values.


By administering bedtime aspirin to those with prehypertension, “we can delay the threshold for reaching hypertensive values,” Dr. Hermida said. “This is a cost-effective and valuable approach to patients with prehypertension.”


Previously, aspirin administered in the evening, but not the morning, had been found to increase the inhibition of platelet aggregation by 62% and inhibit angiotensin II formation by more than 30%. “Aspirin has a significant effect on plasma renin activity,” he said.


The highest values for plasma renin activity occur about three hours after going to bed, which may explain the blood pressure regulation by administering aspirin just prior to bedtime. In addition, the rate of clearance with evening dosing of aspirin is slower compared with morning dosing, he said.


Previous research has also shown that the safety profile of aspirin with respect to bleeding events is also superior with evening dosing, he said.