Diurnal BP patterns may be affected by time of dosing.
In a study of 438 hypertensive adult patients, earlier-morning dose time was positively associated with dipping, which is defined as the normal nighttime drop in blood pressure of at least 10%. Dipping has been shown to be absent more often in African American patients than in whites, reported Dr. David J. Hyman and his colleagues at Baylor College of Medicine, Houston.
The study also confirmed that African Americans tend to be nondippers, and established that Hispanics tend to be nondippers as well.
Average 24-hour ambulatory BP readings (obtained at 30-minute intervals) were similar among the 103 white patients (134.4/78.9 mm Hg), the 200 black patients (134.9/77.4 mm Hg), and the 135 Hispanic patients (132.5/75.7 mm Hg) in the study, all of whom were under treatment for hypertension.
But the absence of a systolic dip was significantly more common in black vs. white men (odds ratio 11.54), and in Hispanic vs. white men (odds ratio 7.32) after adjusting for age, diabetes, and treatment regimen. Similar differences in diastolic dipping were marginally significant (Am. J. Hypertens. 13:884-91, 2004).
Blacks and Hispanics of both genders were from two to three times more likely to be nondippers than were whites, but no significant differences were noted between women in the three ethnic groups, the investigators found.
Of all the treatment variables considered--including age, gender, diabetes, number and type of drugs prescribed, blood pressures, and dose times and regimens--only later-morning dose time (per 1-hour increments) was even marginally associated with risk of nondipping, with odds ratios of 1.29 in men and women for systolic BP, 1.23 in men for diastolic BP, and 1.24 in women for diastolic BP, they noted.
The association was similar in magnitude in women and men, but was significant only in women, owing to the larger number of women in the study.
Although one prior study showed a relationship between evening dosing of certain time-released drugs and dipping, the finding in the Baylor study regarding morning dose time is new; previous studies used uniform morning dose times in a clinic setting, while this study used ambulatory 24-hour monitoring, which allowed patients more discretion in dose timing. The clinical importance of these findings is unclear but is being evaluated in an ongoing study, the investigators noted.
Some of the association between dose time and dipping may be attributable to overlap between the clock times used to define the nighttime interval and the end of dose interval, but there may also be interactions between a patient's dose time and circadian rhythm, they said, noting that the possibility deserves further study.
"At the least, the morning dose time must be taken into account as a potential confounder in future studies of the clinical effectiveness of antihypertensive treatment," Dr. Hyman and his associates said.
BY SHARON WORCESTER
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|Title Annotation:||Cardiovascular Medicine|
|Publication:||Internal Medicine News|
|Date:||Sep 15, 2004|
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