"Timed administration of low-dose aspirin could be a valuable approach not only for the prevention of major cardiovascular events, but also for the control of blood pressure in patients with mild to moderate essential hypertension," said Ramon C. Hermida, Ph.D., of the University of Vigo in Spain, the presenter.

Some studies have examined the anti-hypertensive effects of aspirin, but results have been inconsistent. Dr. Hermida and colleagues speculated that the timing of aspirin administration might be a key factor because many of the physiological pathways affected by the drug have statistically significant circadian rhythms. The body's tendency to absorb aspirin more quickly in the morning than in the evening illustrates this phenomenon.

Dr. Hermida and colleagues followed 109 mildly hypertensive adults who were divided into three groups based on timing of aspirin administration: those who took aspirin upon awakening, those who took it at bedtime, and those who took it according to a non-pharmacological hygienic or dietary recommendation. Blood pressure and heart rate were measured with an ambulatory device every 20 to 30 minutes over a 48-hour period both before and after three months of intervention.

At the end of the study, the participants who took aspirin at bedtime exhibited a highly significant reduction in blood pressure when compared with their cohorts.

"The hypertensives who took aspirin at night on average decreased their systolic blood pressure by 7.0 mm Hg and diastolic blood pressure by 4.8 mm Hg," commented Dr. Hermida. "In contrast, there was no effect on blood pressure when aspirin was administered upon awakening."

The researchers concluded that timing of administration might account for discrepancies in previous studies on the hypertensive effects of aspirin. Moreover, they stressed the importance of identifying patients who are taking aspirin and controlling for the drug's effects in future medical trials involving hypertension.