Beta-blockers lower blood pressure when given as a second drug

Beta-blockers are commonly used in the treatment for high blood pressure (BP). In this review, we asked how much do beta-blockers reduce BP when used as the second drug to treat hypertension. Twenty trials lasting an average of 7 weeks were found in the world scientific literature to answer this question. The data showed that the addition of a beta-blocker to thiazide diuretics or calcium channel blockers reduced BP by 8/6 mmHg when given at doses 2 times the recommended starting dose. When we compared these results with our previous review of the blood pressure lowering effect of thiazide diuretics as second line drug, we found that beta-blockers have a different pattern of BP lowering. This different pattern of effect on blood pressure might explain why first-line beta-blockers appear to be less effective at reducing adverse cardiovascular outcomes than first-line thiazide diuretics, particularly in older individuals.

Authors' conclusions: 

Addition of a beta-blocker to diuretics or calcium-channel blockers reduces BP by 6/4mmHg at 1 times the starting dose and by 8/6 mmHg at 2 times the starting dose. When the blood pressure lowering effect of beta-blockers from this review was compared to that of thiazide diuretics from our previous review (Chen 2009), second-line beta-blockers reduce systolic BP to the same extent as second-line thiazide diuretics, but reduce diastolic BP to a greater degree. The different effect on diastolic BP means that beta-blockers have little or no effect on pulse pressure whereas thiazides cause a significant dose-related decrease in pulse pressure. This difference in the pattern of BP lowering with beta-blockers as compared to thiazides might be the explanation for the fact that beta-blockers appear to be less effective at reducing adverse cardiovascular outcomes than thiazide diuretics, particularly in older individuals.

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Background: 

Beta-blockers are one of the more commonly prescribed classes of anti-hypertensive drugs, both as first-line and second-line.

Objectives: 

To quantify the effect on systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate and withdrawals due to adverse effects of beta-blocker therapy when given as a second-line drug in adult patients with primary hypertension.

Search strategy: 

CENTRAL (The Cochrane Library 2009, Issue 2), MEDLINE (1966-Aug 2009), EMBASE (1988-Aug 2009) and bibliographic citations of articles and reviews were searched.

Selection criteria: 

Double-blind, randomized controlled trials comparing a beta-blocker in combination with a drug from another class of anti-hypertensive drugs compared with that drug alone for a duration of 3 to 12 weeks in patients with primary hypertension were included.

Data collection and analysis: 

Two reviewers independently extracted the data and assessed trial quality of each included study.

Main results: 

20 double-blind RCTs evaluated the BP lowering efficacy of beta-blockers as second-line drug in 3744 hypertensive patients (baseline BP of 158/102 mmHg; mean duration of 7 weeks). The BP reduction from adding a beta-blocker as the second drug was estimated by comparing the difference in BP reduction between the combination and monotherapy groups. A reduction in BP was seen with adding a beta-blocker to thiazide diuretics or calcium channel blockers at doses as low as 0.25 times the manufacturer's recommended starting dose. The BP lowering efficacy of beta-blockers as a second drug was 6/4 mmHg at 1 times the starting dose and 8/6 mmHg at 2 times the starting dose. Beta-blockers reduced heart rate by 10 beats/min at 1 to 2 times the starting dose. Beta-blockers did not statistically significantly increase withdrawals due to adverse effects but this was likely due to the lack of reporting of this outcome in 35% of the included RCTs.

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