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Doctor, When Should I Take My Aspirin?

This study of mildly hypertensive volunteers provides insight about the best timing of aspirin administration.

A previous large, randomized, placebo-controlled trial documented low-dose aspirin's protective effect against adverse cardiovascular events in hypertensive subjects (Journal Watch Cardiology Jul 24 1998). But are the blood-pressure effects of low-dose aspirin dependent on what time of day patients take it?

In this pilot study from Spain, researchers randomized 100 untreated mildly hypertensive volunteers (mean baseline BP, 144/85 mm Hg) to 1 of 3 interventions: nonpharmacologic hygienic-dietary recommendations (HDRs) about sodium restriction, diet, alcohol intake, and exercise; the same HDRs plus 100 mg per day of aspirin taken upon awakening; or the HDRs plus 100 mg per day of aspirin taken before bedtime. Before intervention and 3 months after intervention, ambulatory BP was measured automatically with a device every 20 minutes during the day and every 30 minutes at night for 48 consecutive hours.

Baseline characteristics, including BP, did not differ significantly among the groups. From preintervention to 3 months postintervention, 24-hour mean BP did not change significantly in the HDR-only group or in the aspirin-on-awakening group; however, BP decreased by 6.2/4.1 mm Hg in the aspirin-at-bedtime group -- a significant difference from baseline and from the other 2 groups.

Comment: The results of this small pilot study in mildly hypertensive people suggest that low-dose aspirin lowers blood pressure as a function of the timing of administration in relation to the rest-activity cycle. Findings might be different in patients who also are receiving treatment with other antihypertensive drugs. Given the widespread use of aspirin for cardiovascular protection, larger studies are warranted to see whether the BP-lowering effect of aspirin only at bedtime holds up.

— Joel M. Gore, MD

Published in Journal Watch Cardiology August 1, 2003

Citation(s):

Hermida RC et al. Administration time-dependent effects of aspirin on blood pressure in untreated hypertensive patients. Hypertension 2003 Jun; 41:1259-67.

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